diff --git a/src/analyses/goto_check.cpp b/src/analyses/goto_check.cpp
index 8fe596d9262..be4edbf288f 100644
--- a/src/analyses/goto_check.cpp
+++ b/src/analyses/goto_check.cpp
@@ -37,7 +37,7 @@ class goto_checkt
     const namespacet &_ns,
     const optionst &_options):
     ns(_ns),
-    local_bitvector_analysis(0)
+    local_bitvector_analysis(nullptr)
   {
     enable_bounds_check=_options.get_bool_option("bounds-check");
     enable_pointer_check=_options.get_bool_option("pointer-check");
diff --git a/src/analyses/goto_rw.cpp b/src/analyses/goto_rw.cpp
index be3ef3e0a8d..49827bd2bd3 100644
--- a/src/analyses/goto_rw.cpp
+++ b/src/analyses/goto_rw.cpp
@@ -463,9 +463,10 @@ void rw_range_sett::add(
 {
   objectst::iterator entry=(mode==get_modet::LHS_W ? w_range_set : r_range_set).
     insert(
-      std::pair<const irep_idt&, range_domain_baset*>(identifier, 0)).first;
+      std::pair<const irep_idt&, range_domain_baset*>(
+        identifier, nullptr)).first;
 
-  if(entry->second==0)
+  if(entry->second==nullptr)
     entry->second=new range_domaint();
 
   static_cast<range_domaint*>(entry->second)->push_back(
@@ -663,9 +664,10 @@ void rw_guarded_range_set_value_sett::add(
 {
   objectst::iterator entry=(mode==get_modet::LHS_W ? w_range_set : r_range_set).
     insert(
-      std::pair<const irep_idt&, range_domain_baset*>(identifier, 0)).first;
+      std::pair<const irep_idt&, range_domain_baset*>(
+        identifier, nullptr)).first;
 
-  if(entry->second==0)
+  if(entry->second==nullptr)
     entry->second=new guarded_range_domaint();
 
   static_cast<guarded_range_domaint*>(entry->second)->insert(
diff --git a/src/analyses/goto_rw.h b/src/analyses/goto_rw.h
index 06b7a7ab411..1f92c3e0e14 100644
--- a/src/analyses/goto_rw.h
+++ b/src/analyses/goto_rw.h
@@ -108,7 +108,7 @@ class rw_range_sett
 
   const range_domaint &get_ranges(objectst::const_iterator it) const
   {
-    assert(dynamic_cast<range_domaint*>(it->second)!=0);
+    PRECONDITION(dynamic_cast<range_domaint*>(it->second)!=nullptr);
     return *static_cast<range_domaint*>(it->second);
   }
 
@@ -277,7 +277,7 @@ class rw_guarded_range_set_value_sett:public rw_range_set_value_sett
 
   const guarded_range_domaint &get_ranges(objectst::const_iterator it) const
   {
-    assert(dynamic_cast<guarded_range_domaint*>(it->second)!=0);
+    PRECONDITION(dynamic_cast<guarded_range_domaint*>(it->second)!=nullptr);
     return *static_cast<guarded_range_domaint*>(it->second);
   }
 
diff --git a/src/analyses/invariant_set.cpp b/src/analyses/invariant_set.cpp
index 6127abdd57f..a91c0349bbb 100644
--- a/src/analyses/invariant_set.cpp
+++ b/src/analyses/invariant_set.cpp
@@ -13,6 +13,7 @@ Author: Daniel Kroening, kroening@kroening.com
 
 #include <iostream>
 
+#include <util/base_exceptions.h>
 #include <util/symbol_table.h>
 #include <util/namespace.h>
 #include <util/arith_tools.h>
@@ -144,7 +145,7 @@ bool invariant_sett::get_object(
   const exprt &expr,
   unsigned &n) const
 {
-  assert(object_store!=NULL);
+  PRECONDITION(object_store!=nullptr);
   return object_store->get(expr, n);
 }
 
@@ -315,7 +316,8 @@ void invariant_sett::output(
     return;
   }
 
-  assert(object_store!=NULL);
+  INVARIANT_STRUCTURED(
+    object_store!=nullptr, nullptr_exceptiont, "Object store is null");
 
   for(unsigned i=0; i<eq_set.size(); i++)
     if(eq_set.is_root(i) &&
@@ -899,7 +901,7 @@ std::string invariant_sett::to_string(
   unsigned a,
   const irep_idt &identifier) const
 {
-  assert(object_store!=NULL);
+  PRECONDITION(object_store!=nullptr);
   return object_store->to_string(a, identifier);
 }
 
diff --git a/src/analyses/invariant_set.h b/src/analyses/invariant_set.h
index 6bb40bd3e94..b65ce7897f3 100644
--- a/src/analyses/invariant_set.h
+++ b/src/analyses/invariant_set.h
@@ -98,9 +98,9 @@ class invariant_sett
   invariant_sett():
     threaded(false),
     is_false(false),
-    value_sets(NULL),
-    object_store(NULL),
-    ns(NULL)
+    value_sets(nullptr),
+    object_store(nullptr),
+    ns(nullptr)
   {
   }
 
diff --git a/src/analyses/local_may_alias.h b/src/analyses/local_may_alias.h
index b54cf4e9e88..5e04ff01a75 100644
--- a/src/analyses/local_may_alias.h
+++ b/src/analyses/local_may_alias.h
@@ -94,7 +94,7 @@ class local_may_aliast
 class local_may_alias_factoryt
 {
 public:
-  local_may_alias_factoryt():goto_functions(NULL)
+  local_may_alias_factoryt():goto_functions(nullptr)
   {
   }
 
@@ -109,7 +109,7 @@ class local_may_alias_factoryt
 
   local_may_aliast &operator()(const irep_idt &fkt)
   {
-    assert(goto_functions!=NULL);
+    PRECONDITION(goto_functions!=nullptr);
     fkt_mapt::iterator f_it=fkt_map.find(fkt);
     if(f_it!=fkt_map.end())
       return *f_it->second;
diff --git a/src/analyses/reaching_definitions.cpp b/src/analyses/reaching_definitions.cpp
index 0e0462c3c8a..89b31da543b 100644
--- a/src/analyses/reaching_definitions.cpp
+++ b/src/analyses/reaching_definitions.cpp
@@ -51,7 +51,10 @@ void rd_range_domaint::transform(
 {
   reaching_definitions_analysist *rd=
     dynamic_cast<reaching_definitions_analysist*>(&ai);
-  assert(rd!=0);
+  INVARIANT_STRUCTURED(
+    rd!=nullptr,
+    bad_cast_exceptiont,
+    "ai has type reaching_definitions_analysist");
 
   assert(bv_container);
 
@@ -298,7 +301,10 @@ void rd_range_domaint::transform_assign(
     const symbolt *symbol_ptr;
     if(ns.lookup(identifier, symbol_ptr))
       continue;
-    assert(symbol_ptr!=0);
+    INVARIANT_STRUCTURED(
+      symbol_ptr!=nullptr,
+      nullptr_exceptiont,
+      "Symbol is in symbol table");
 
     const range_domaint &ranges=rw_set.get_ranges(it);
 
diff --git a/src/analyses/reaching_definitions.h b/src/analyses/reaching_definitions.h
index e5f0d5f12b5..21cbd1ed377 100644
--- a/src/analyses/reaching_definitions.h
+++ b/src/analyses/reaching_definitions.h
@@ -16,6 +16,7 @@ Date: February 2013
 #ifndef CPROVER_ANALYSES_REACHING_DEFINITIONS_H
 #define CPROVER_ANALYSES_REACHING_DEFINITIONS_H
 
+#include <util/base_exceptions.h>
 #include <util/threeval.h>
 
 #include "ai.h"
@@ -102,7 +103,7 @@ class rd_range_domaint:public ai_domain_baset
   rd_range_domaint():
     ai_domain_baset(),
     has_values(false),
-    bv_container(0)
+    bv_container(nullptr)
   {
   }
 
@@ -243,9 +244,9 @@ class reaching_definitions_analysist:
   explicit reaching_definitions_analysist(const namespacet &_ns):
     concurrency_aware_ait<rd_range_domaint>(),
     ns(_ns),
-    value_sets(0),
-    is_threaded(0),
-    is_dirty(0)
+    value_sets(nullptr),
+    is_threaded(nullptr),
+    is_dirty(nullptr)
   {
   }
 
@@ -259,7 +260,10 @@ class reaching_definitions_analysist:
     statet &s=concurrency_aware_ait<rd_range_domaint>::get_state(l);
 
     rd_range_domaint *rd_state=dynamic_cast<rd_range_domaint*>(&s);
-    assert(rd_state!=0);
+    INVARIANT_STRUCTURED(
+      rd_state!=nullptr,
+      bad_cast_exceptiont,
+      "rd_state has type rd_range_domaint");
 
     rd_state->set_bitvector_container(*this);
 
diff --git a/src/ansi-c/c_preprocess.cpp b/src/ansi-c/c_preprocess.cpp
index 6ba8e6f359b..927a928b187 100644
--- a/src/ansi-c/c_preprocess.cpp
+++ b/src/ansi-c/c_preprocess.cpp
@@ -344,7 +344,7 @@ bool c_preprocess(
 static bool is_dot_i_file(const std::string &path)
 {
   const char *ext=strrchr(path.c_str(), '.');
-  if(ext==NULL)
+  if(ext==nullptr)
     return false;
   if(std::string(ext)==".i" ||
      std::string(ext)==".ii")
@@ -889,7 +889,7 @@ bool c_preprocess_gcc_clang(
 
   FILE *stream=popen(command.c_str(), "r");
 
-  if(stream!=NULL)
+  if(stream!=nullptr)
   {
     int ch;
     while((ch=fgetc(stream))!=EOF)
@@ -1011,7 +1011,7 @@ bool c_preprocess_arm(
 
   FILE *stream=popen(command.c_str(), "r");
 
-  if(stream!=NULL)
+  if(stream!=nullptr)
   {
     int ch;
     while((ch=fgetc(stream))!=EOF)
diff --git a/src/ansi-c/cprover_library.cpp b/src/ansi-c/cprover_library.cpp
index 8f99f987bf3..f13e321d752 100644
--- a/src/ansi-c/cprover_library.cpp
+++ b/src/ansi-c/cprover_library.cpp
@@ -38,7 +38,7 @@ std::string get_cprover_library_text(
   std::size_t count=0;
 
   for(cprover_library_entryt *e=cprover_library;
-      e->function!=NULL;
+      e->function!=nullptr;
       e++)
   {
     irep_idt id=e->function;
diff --git a/src/ansi-c/expr2c.cpp b/src/ansi-c/expr2c.cpp
index 9c980cc842a..d1dbf3bb6b5 100644
--- a/src/ansi-c/expr2c.cpp
+++ b/src/ansi-c/expr2c.cpp
@@ -2664,7 +2664,7 @@ std::string expr2ct::convert_code_decl(
 
   std::string dest=indent_str(indent);
 
-  const symbolt *symbol=0;
+  const symbolt *symbol=nullptr;
   if(!ns.lookup(to_symbol_expr(src.op0()).get_identifier(), symbol))
   {
     if(symbol->is_file_local &&
diff --git a/src/cbmc/cbmc_parse_options.cpp b/src/cbmc/cbmc_parse_options.cpp
index 2943d9a18d7..2e21dae825b 100644
--- a/src/cbmc/cbmc_parse_options.cpp
+++ b/src/cbmc/cbmc_parse_options.cpp
@@ -569,7 +569,7 @@ int cbmc_parse_optionst::get_goto_program(
 
       languaget *language=get_language_from_filename(filename);
 
-      if(language==NULL)
+      if(language==nullptr)
       {
         error() << "failed to figure out type of file `"
                 <<  filename << "'" << eom;
@@ -718,7 +718,7 @@ void cbmc_parse_optionst::preprocessing()
 
     languaget *ptr=get_language_from_filename(filename);
 
-    if(ptr==NULL)
+    if(ptr==nullptr)
     {
       error() << "failed to figure out type of file" << eom;
       return;
diff --git a/src/clobber/clobber_parse_options.cpp b/src/clobber/clobber_parse_options.cpp
index 36cc3e49abc..8c2b2dc1f50 100644
--- a/src/clobber/clobber_parse_options.cpp
+++ b/src/clobber/clobber_parse_options.cpp
@@ -250,7 +250,7 @@ bool clobber_parse_optionst::get_goto_program(
 
       languaget *language=get_language_from_filename(filename);
 
-      if(language==NULL)
+      if(language==nullptr)
       {
         error() << "failed to figure out type of file `" <<  filename << "'"
                 << eom;
diff --git a/src/cpp/cpp_id.cpp b/src/cpp/cpp_id.cpp
index e6c13ca4cfb..edcc139ce4f 100644
--- a/src/cpp/cpp_id.cpp
+++ b/src/cpp/cpp_id.cpp
@@ -24,7 +24,7 @@ cpp_idt::cpp_idt():
   id_class(id_classt::UNKNOWN),
   this_expr(static_cast<const exprt &>(get_nil_irep())),
   compound_counter(0),
-  parent(NULL)
+  parent(nullptr)
 {
 }
 
diff --git a/src/cpp/cpp_id.h b/src/cpp/cpp_id.h
index f7fe339cc1a..b2efbc27188 100644
--- a/src/cpp/cpp_id.h
+++ b/src/cpp/cpp_id.h
@@ -20,6 +20,7 @@ Author: Daniel Kroening, kroening@cs.cmu.edu
 #include <iosfwd>
 
 #include <util/expr.h>
+#include <util/invariant.h>
 #include <util/std_types.h>
 
 class cpp_scopet;
@@ -81,7 +82,7 @@ class cpp_idt
 
   cpp_idt &get_parent() const
   {
-    assert(parent!=NULL);
+    PRECONDITION(parent!=nullptr);
     return *parent;
   }
 
diff --git a/src/cpp/cpp_instantiate_template.cpp b/src/cpp/cpp_instantiate_template.cpp
index c28fe5ca546..fe0b3e28ac2 100644
--- a/src/cpp/cpp_instantiate_template.cpp
+++ b/src/cpp/cpp_instantiate_template.cpp
@@ -12,6 +12,7 @@ Author: Daniel Kroening, kroening@cs.cmu.edu
 #include "cpp_typecheck.h"
 
 #include <util/arith_tools.h>
+#include <util/base_exceptions.h>
 #include <util/simplify_expr.h>
 
 #include <util/c_types.h>
@@ -130,7 +131,8 @@ const symbolt &cpp_typecheckt::class_template_symbol(
   cpp_scopet *template_scope=
     static_cast<cpp_scopet *>(cpp_scopes.id_map[template_symbol.name]);
 
-  assert(template_scope!=NULL);
+  INVARIANT_STRUCTURED(
+    template_scope!=nullptr, nullptr_exceptiont, "template_scope is null");
 
   irep_idt identifier=
     id2string(template_scope->prefix)+
@@ -276,7 +278,7 @@ const symbolt &cpp_typecheckt::instantiate_template(
   cpp_scopet *template_scope=
     static_cast<cpp_scopet *>(cpp_scopes.id_map[template_symbol.name]);
 
-  if(template_scope==NULL)
+  if(template_scope==nullptr)
   {
     error().source_location=source_location;
     error() << "identifier: " << template_symbol.name << '\n'
@@ -284,7 +286,8 @@ const symbolt &cpp_typecheckt::instantiate_template(
     throw 0;
   }
 
-  assert(template_scope!=NULL);
+  INVARIANT_STRUCTURED(
+    template_scope!=nullptr, nullptr_exceptiont, "template_scope is null");
 
   // produce new declaration
   cpp_declarationt new_decl=to_cpp_declaration(template_symbol.type);
diff --git a/src/cpp/cpp_language.cpp b/src/cpp/cpp_language.cpp
index 59e538265cb..c8b7f999653 100644
--- a/src/cpp/cpp_language.cpp
+++ b/src/cpp/cpp_language.cpp
@@ -65,7 +65,7 @@ bool cpp_languaget::preprocess(
   // check extension
 
   const char *ext=strrchr(path.c_str(), '.');
-  if(ext!=NULL && std::string(ext)==".ipp")
+  if(ext!=nullptr && std::string(ext)==".ipp")
   {
     std::ifstream infile(path);
 
diff --git a/src/cpp/cpp_typecheck_compound_type.cpp b/src/cpp/cpp_typecheck_compound_type.cpp
index 36d2a2e70b6..39f229bfbea 100644
--- a/src/cpp/cpp_typecheck_compound_type.cpp
+++ b/src/cpp/cpp_typecheck_compound_type.cpp
@@ -110,7 +110,7 @@ void cpp_typecheckt::typecheck_compound_type(
   // get the tag name
   bool has_tag=type.find(ID_tag).is_not_nil();
   irep_idt base_name;
-  cpp_scopet *dest_scope=NULL;
+  cpp_scopet *dest_scope=nullptr;
   bool has_body=type.find(ID_body).is_not_nil();
   bool tag_only_declaration=type.get_bool(ID_C_tag_only_declaration);
 
diff --git a/src/cpp/cpp_typecheck_expr.cpp b/src/cpp/cpp_typecheck_expr.cpp
index 87f15a16a3b..88b26461482 100644
--- a/src/cpp/cpp_typecheck_expr.cpp
+++ b/src/cpp/cpp_typecheck_expr.cpp
@@ -471,7 +471,7 @@ struct operator_entryt
   { ID_notequal, "!=" },
   { ID_dereference, "*" },
   { ID_ptrmember, "->" },
-  { irep_idt(), NULL }
+  { irep_idt(), nullptr }
 };
 
 bool cpp_typecheckt::operator_is_overloaded(exprt &expr)
diff --git a/src/cpp/cpp_typecheck_resolve.cpp b/src/cpp/cpp_typecheck_resolve.cpp
index 28d42e6af62..d8e0e8c3d90 100644
--- a/src/cpp/cpp_typecheck_resolve.cpp
+++ b/src/cpp/cpp_typecheck_resolve.cpp
@@ -1117,7 +1117,7 @@ symbol_typet cpp_typecheck_resolvet::disambiguate_template_classes(
       static_cast<cpp_scopet *>(
         cpp_typecheck.cpp_scopes.id_map[id]);
 
-    if(template_scope==NULL)
+    if(template_scope==nullptr)
     {
       cpp_typecheck.error().source_location=source_location;
       cpp_typecheck.error() << "template identifier: " << id << '\n'
@@ -1959,7 +1959,7 @@ exprt cpp_typecheck_resolvet::guess_function_template_args(
     static_cast<cpp_scopet *>(
       cpp_typecheck.cpp_scopes.id_map[template_identifier]);
 
-  if(template_scope==NULL)
+  if(template_scope==nullptr)
   {
     cpp_typecheck.error().source_location=source_location;
     cpp_typecheck.error() << "template identifier: "
diff --git a/src/cpp/cpp_typecheck_template.cpp b/src/cpp/cpp_typecheck_template.cpp
index 47ebd7f006e..7c464208265 100644
--- a/src/cpp/cpp_typecheck_template.cpp
+++ b/src/cpp/cpp_typecheck_template.cpp
@@ -11,6 +11,7 @@ Author: Daniel Kroening, kroening@cs.cmu.edu
 
 #include "cpp_typecheck.h"
 
+#include <util/base_exceptions.h>
 #include <util/simplify_expr.h>
 
 #include "cpp_type2name.h"
@@ -910,7 +911,8 @@ cpp_template_args_tct cpp_typecheckt::typecheck_template_args(
       // these need to be typechecked in the scope of the template,
       // not in the current scope!
       cpp_idt *template_scope=cpp_scopes.id_map[template_symbol.name];
-      assert(template_scope!=NULL);
+      INVARIANT_STRUCTURED(
+        template_scope!=nullptr, nullptr_exceptiont, "template_scope is null");
       cpp_scopes.go_to(*template_scope);
     }
 
@@ -960,7 +962,10 @@ cpp_template_args_tct cpp_typecheckt::typecheck_template_args(
       {
         cpp_save_scopet cpp_saved_scope(cpp_scopes);
         cpp_idt *template_scope=cpp_scopes.id_map[template_symbol.name];
-        assert(template_scope!=NULL);
+        INVARIANT_STRUCTURED(
+          template_scope!=nullptr,
+          nullptr_exceptiont,
+          "template_scope is null");
         cpp_scopes.go_to(*template_scope);
         typecheck_type(type);
       }
diff --git a/src/cpp/parse.cpp b/src/cpp/parse.cpp
index 87e9ad099d7..d0c2e01ecf2 100644
--- a/src/cpp/parse.cpp
+++ b/src/cpp/parse.cpp
@@ -48,7 +48,7 @@ struct indenter // NOLINT(readability/identifiers)
 class new_scopet
 {
 public:
-  new_scopet():kind(kindt::NONE), anon_count(0), parent(NULL)
+  new_scopet():kind(kindt::NONE), anon_count(0), parent(nullptr)
   {
   }
 
@@ -155,7 +155,7 @@ class new_scopet
 
   std::string full_name() const
   {
-    return (parent==NULL?"":(parent->full_name()+"::"))+
+    return (parent==nullptr?"":(parent->full_name()+"::"))+
            id2string(id);
   }
 
diff --git a/src/goto-cc/armcc_cmdline.cpp b/src/goto-cc/armcc_cmdline.cpp
index 9cb3fccfd03..d0a16ac95a0 100644
--- a/src/goto-cc/armcc_cmdline.cpp
+++ b/src/goto-cc/armcc_cmdline.cpp
@@ -192,7 +192,7 @@ static const char *options_no_arg[]=
   "--translate_gcc",
   "--translate_gld",
   "-W",
-  NULL
+  nullptr
 };
 
 static const char *options_with_prefix[]=
@@ -242,7 +242,7 @@ static const char *options_with_prefix[]=
   "--configure_cpp_headers=",
   "--configure_extra_includes=",
   "--configure_extra_libraries=",
-  NULL
+  nullptr
 };
 
 static const char *options_with_arg[]=
@@ -262,7 +262,7 @@ static const char *options_with_arg[]=
   "-o",
   "--cpu",
   "--apcs",
-  NULL
+  nullptr
 };
 
 bool armcc_cmdlinet::parse(int argc, const char **argv)
diff --git a/src/goto-cc/as86_cmdline.cpp b/src/goto-cc/as86_cmdline.cpp
index e60f0152bc0..dce3deecf2c 100644
--- a/src/goto-cc/as86_cmdline.cpp
+++ b/src/goto-cc/as86_cmdline.cpp
@@ -23,7 +23,7 @@ const char *goto_as86_options_with_argument[]=
   "--function",
   "--native-assembler",
   "--print-rejected-preprocessed-source",
-  NULL
+  nullptr
 };
 
 const char *as86_options_without_argument[]=
@@ -40,7 +40,7 @@ const char *as86_options_without_argument[]=
   "-u-", // both -u and -u- seem to be accepted
   "-v",
   "-w-",
-  NULL
+  nullptr
 };
 
 const char *as86_options_with_argument[]=
@@ -52,7 +52,7 @@ const char *as86_options_with_argument[]=
   "-b",
   "-s",
   "-t",
-  NULL
+  nullptr
 };
 
 bool as86_cmdlinet::parse(int argc, const char **argv)
@@ -75,7 +75,7 @@ bool as86_cmdlinet::parse(int argc, const char **argv)
 
     // separated only, and also allow concatenation with "="
     for(const char **o=goto_as86_options_with_argument;
-        *o!=NULL && !found;
+        *o!=nullptr && !found;
         ++o)
     {
       std::string os(*o);
@@ -113,7 +113,7 @@ bool as86_cmdlinet::parse(int argc, const char **argv)
     }
 
     for(const char **o=as86_options_with_argument;
-        *o!=NULL && !found;
+        *o!=nullptr && !found;
         ++o)
     {
       std::string os(*o);
diff --git a/src/goto-cc/as_cmdline.cpp b/src/goto-cc/as_cmdline.cpp
index 172b281458f..2c22cfc70df 100644
--- a/src/goto-cc/as_cmdline.cpp
+++ b/src/goto-cc/as_cmdline.cpp
@@ -23,7 +23,7 @@ const char *goto_as_options_with_argument[]=
   "--function",
   "--native-assembler",
   "--print-rejected-preprocessed-source",
-  NULL
+  nullptr
 };
 
 const char *as_options_without_argument[]=
@@ -59,7 +59,7 @@ const char *as_options_without_argument[]=
   "--32", // i386
   "--64", // i386
   "-n", // i386
-  NULL
+  nullptr
 };
 
 const char *as_options_with_argument[]=
@@ -74,7 +74,7 @@ const char *as_options_with_argument[]=
   "-o",
   "-march", // i386
   "-mtune", // i386
-  NULL
+  nullptr
 };
 
 bool as_cmdlinet::parse(int argc, const char **argv)
@@ -104,7 +104,7 @@ bool as_cmdlinet::parse(int argc, const char **argv)
 
     // separated only, and also allow concatenation with "="
     for(const char **o=goto_as_options_with_argument;
-        *o!=NULL && !found;
+        *o!=nullptr && !found;
         ++o)
     {
       std::string os(*o);
@@ -170,7 +170,7 @@ bool as_cmdlinet::parse(int argc, const char **argv)
     }
 
     for(const char **o=as_options_with_argument;
-        *o!=NULL && !found;
+        *o!=nullptr && !found;
         ++o)
     {
       std::string os(*o);
diff --git a/src/goto-cc/bcc_cmdline.cpp b/src/goto-cc/bcc_cmdline.cpp
index c4cbbc80b3f..f4c0626b142 100644
--- a/src/goto-cc/bcc_cmdline.cpp
+++ b/src/goto-cc/bcc_cmdline.cpp
@@ -24,7 +24,7 @@ const char *goto_bcc_options_with_argument[]=
   "--native-compiler",
   "--native-linker",
   "--print-rejected-preprocessed-source",
-  NULL
+  nullptr
 };
 
 const char *bcc_options_without_argument[]=
@@ -46,7 +46,7 @@ const char *bcc_options_without_argument[]=
   "-x",
   "-W",
   "-ansi",
-  NULL
+  nullptr
 };
 
 const char *bcc_options_with_argument[]=
@@ -64,7 +64,7 @@ const char *bcc_options_with_argument[]=
   "-T",
   "-Q",
   "-t",
-  NULL
+  nullptr
 };
 
 bool bcc_cmdlinet::parse(int argc, const char **argv)
@@ -87,7 +87,7 @@ bool bcc_cmdlinet::parse(int argc, const char **argv)
 
     // separated only, and also allow concatenation with "="
     for(const char **o=goto_bcc_options_with_argument;
-        *o!=NULL && !found;
+        *o!=nullptr && !found;
         ++o)
     {
       std::string os(*o);
@@ -125,7 +125,7 @@ bool bcc_cmdlinet::parse(int argc, const char **argv)
     }
 
     for(const char **o=bcc_options_with_argument;
-        *o!=NULL && !found;
+        *o!=nullptr && !found;
         ++o)
     {
       std::string os(*o);
diff --git a/src/goto-cc/compile.cpp b/src/goto-cc/compile.cpp
index 96b76260e96..d5dcf8b5704 100644
--- a/src/goto-cc/compile.cpp
+++ b/src/goto-cc/compile.cpp
@@ -232,7 +232,7 @@ bool compilet::add_input_file(const std::string &file_name)
 
     stream=popen(cmd.str().c_str(), "r");
 
-    if(stream!=NULL)
+    if(stream!=nullptr)
     {
       std::string line;
       int ch; // fgetc returns an int, not char
@@ -472,7 +472,7 @@ bool compilet::parse(const std::string &file_name)
   else
     languagep=get_language_from_filename(file_name);
 
-  if(languagep==NULL)
+  if(languagep==nullptr)
   {
     error() << "failed to figure out type of file `" << file_name << "'" << eom;
     return true;
diff --git a/src/goto-cc/gcc_cmdline.cpp b/src/goto-cc/gcc_cmdline.cpp
index c5b4057ed14..e4b2bb1ddb6 100644
--- a/src/goto-cc/gcc_cmdline.cpp
+++ b/src/goto-cc/gcc_cmdline.cpp
@@ -29,7 +29,7 @@ const char *goto_cc_options_with_separated_argument[]=
   "--native-compiler",
   "--native-linker",
   "--print-rejected-preprocessed-source",
-  NULL
+  nullptr
 };
 
 // non-gcc options
@@ -52,7 +52,7 @@ const char *goto_cc_options_without_argument[]=
   "--no-arch",
   "--partial-inlining",
   "-?",
-  NULL
+  nullptr
 };
 
 // separated or concatenated
@@ -75,7 +75,7 @@ const char *gcc_options_with_argument[]=
   "-U",
   "-u", // goes to linker
   "-T", // goes to linker
-  NULL
+  nullptr
 };
 
 const char *gcc_options_with_separated_argument[]=
@@ -107,7 +107,7 @@ const char *gcc_options_with_separated_argument[]=
   "-current_version", // on the Mac
   "-compatibility_version",  // on the Mac
   "-z",
-  NULL
+  nullptr
 };
 
 const char *gcc_options_with_concatenated_argument[]=
@@ -115,7 +115,7 @@ const char *gcc_options_with_concatenated_argument[]=
   "-d",
   "-g",
   "-A",
-  NULL
+  nullptr
 };
 
 const char *gcc_options_without_argument[]=
@@ -209,7 +209,7 @@ const char *gcc_options_without_argument[]=
   "-EB",
   "-EL",
   "-fast", // Apple only
-  NULL
+  nullptr
 };
 
 bool gcc_cmdlinet::parse(int argc, const char **argv)
@@ -282,7 +282,7 @@ bool gcc_cmdlinet::parse_arguments(
 
       // separated only, and also allow concatenation with "="
       for(const char **o=goto_cc_options_with_separated_argument;
-          *o!=NULL && !found;
+          *o!=nullptr && !found;
           ++o)
       {
         if(argv_i==*o) // separated
@@ -354,7 +354,7 @@ bool gcc_cmdlinet::parse_arguments(
 
       // separated only, and also allow concatenation with "="
       for(const char **o=gcc_options_with_separated_argument;
-          *o!=NULL && !found;
+          *o!=nullptr && !found;
           ++o)
       {
         if(argv_i==*o) // separated
@@ -380,7 +380,7 @@ bool gcc_cmdlinet::parse_arguments(
 
       // concatenated _or_ separated, e.g., -I
       for(const char **o=gcc_options_with_argument;
-          *o!=NULL && !found;
+          *o!=nullptr && !found;
           ++o)
       {
         if(argv_i==*o) // separated
@@ -405,7 +405,7 @@ bool gcc_cmdlinet::parse_arguments(
 
       // concatenated only
       for(const char **o=gcc_options_with_concatenated_argument;
-          *o!=NULL && !found;
+          *o!=nullptr && !found;
           ++o)
       {
         if(has_prefix(argv_i, *o)) // concatenated
diff --git a/src/goto-cc/goto_cc_cmdline.cpp b/src/goto-cc/goto_cc_cmdline.cpp
index 71bb06f8160..cb030366e3f 100644
--- a/src/goto-cc/goto_cc_cmdline.cpp
+++ b/src/goto-cc/goto_cc_cmdline.cpp
@@ -29,7 +29,7 @@ goto_cc_cmdlinet::~goto_cc_cmdlinet()
 
 bool goto_cc_cmdlinet::in_list(const char *option, const char **list)
 {
-  for(std::size_t i=0; list[i]!=NULL; i++)
+  for(std::size_t i=0; list[i]!=nullptr; i++)
   {
     if(strcmp(option, list[i])==0)
       return true;
@@ -43,7 +43,7 @@ bool goto_cc_cmdlinet::prefix_in_list(
   const char **list,
   std::string &prefix)
 {
-  for(std::size_t i=0; list[i]!=NULL; i++)
+  for(std::size_t i=0; list[i]!=nullptr; i++)
   {
     if(strncmp(option, list[i], strlen(list[i]))==0)
     {
diff --git a/src/goto-cc/goto_cc_main.cpp b/src/goto-cc/goto_cc_main.cpp
index ebe885a37a3..8d3e4222194 100644
--- a/src/goto-cc/goto_cc_main.cpp
+++ b/src/goto-cc/goto_cc_main.cpp
@@ -48,7 +48,7 @@ int main(int argc, const char **argv)
   const char **argv=narrow_argv(argc, argv_wide);
   #endif
 
-  if(argv==NULL || argc<1)
+  if(argv==nullptr || argc<1)
   {
     std::cerr << "failed to determine base name\n";
     return 1;
diff --git a/src/goto-cc/ld_cmdline.cpp b/src/goto-cc/ld_cmdline.cpp
index 1f17dabd105..c77ee68773b 100644
--- a/src/goto-cc/ld_cmdline.cpp
+++ b/src/goto-cc/ld_cmdline.cpp
@@ -24,7 +24,7 @@ const char *goto_ld_options_with_argument[]=
   "--verbosity",
   "--native-compiler",
   "--native-linker",
-  NULL
+  nullptr
 };
 
 const char *ld_options_with_argument[]=
@@ -99,7 +99,7 @@ const char *ld_options_with_argument[]=
   "--ios_version_min", // Apple only
   "--macosx_version_min", // Apple only
   "--install_name", // Apple only
-  NULL
+  nullptr
 };
 
 const char *ld_options_without_argument[]=
@@ -233,7 +233,7 @@ const char *ld_options_without_argument[]=
   "--dylib", // Apple only
   "--dylinker", // Apple only
   "--bundle", // Apple only
-  NULL
+  nullptr
 };
 
 bool ld_cmdlinet::parse(int argc, const char **argv)
@@ -262,7 +262,7 @@ bool ld_cmdlinet::parse(int argc, const char **argv)
     bool found=false;
 
     for(const char **o=goto_ld_options_with_argument;
-        *o!=NULL && !found;
+        *o!=nullptr && !found;
         ++o)
     {
       std::string os(*o);
@@ -299,7 +299,7 @@ bool ld_cmdlinet::parse(int argc, const char **argv)
 
     // also store in cmdlinet
 
-    for(const char **o=ld_options_without_argument; *o!=NULL && !found; o++)
+    for(const char **o=ld_options_without_argument; *o!=nullptr && !found; o++)
     {
       std::string os(*o);
       // ld accepts all long options also as short option
@@ -316,7 +316,7 @@ bool ld_cmdlinet::parse(int argc, const char **argv)
     // 2) concatenated with '=' for long options
     // 3) separate
 
-    for(const char **o=ld_options_with_argument; *o!=NULL && !found; o++)
+    for(const char **o=ld_options_with_argument; *o!=nullptr && !found; o++)
     {
       std::string os(*o);
 
diff --git a/src/goto-cc/ms_cl_cmdline.cpp b/src/goto-cc/ms_cl_cmdline.cpp
index ea605ef6d82..cdc9458bb0c 100644
--- a/src/goto-cc/ms_cl_cmdline.cpp
+++ b/src/goto-cc/ms_cl_cmdline.cpp
@@ -44,7 +44,7 @@ const char *non_ms_cl_options[]=
   "--partial-inlining",
   "--verbosity",
   "--function",
-  NULL
+  nullptr
 };
 
 bool ms_cl_cmdlinet::parse(const std::vector<std::string> &options)
@@ -110,7 +110,7 @@ void ms_cl_cmdlinet::parse_env()
 
   const char *CL_env=getenv("CL");
 
-  if(CL_env!=NULL)
+  if(CL_env!=nullptr)
     process_response_file_line(CL_env);
 
   #endif
@@ -275,7 +275,7 @@ void ms_cl_cmdlinet::process_non_cl_option(
 {
   set(s);
 
-  for(unsigned j=0; non_ms_cl_options[j]!=NULL; j++)
+  for(unsigned j=0; non_ms_cl_options[j]!=nullptr; j++)
     if(s==non_ms_cl_options[j])
       return;
 
@@ -288,7 +288,7 @@ void ms_cl_cmdlinet::process_non_cl_option(
 const char *ms_cl_flags[]=
 {
   "c", // compile only
-  NULL
+  nullptr
 };
 
 const char *ms_cl_prefixes[]=
@@ -406,7 +406,7 @@ const char *ms_cl_prefixes[]=
   "MT", //  link with LIBCMT.LIB
   "MDd", //  link with MSVCRTD.LIB debug lib
   "MTd", //  link with LIBCMTD.LIB debug lib
-  NULL
+  nullptr
 };
 
 void ms_cl_cmdlinet::process_cl_option(const std::string &s)
@@ -420,7 +420,7 @@ void ms_cl_cmdlinet::process_cl_option(const std::string &s)
     return;
   }
 
-  for(std::size_t j=0; ms_cl_flags[j]!=NULL; j++)
+  for(std::size_t j=0; ms_cl_flags[j]!=nullptr; j++)
   {
     if(std::string(s, 1, std::string::npos)==ms_cl_flags[j])
     {
@@ -453,7 +453,7 @@ void ms_cl_cmdlinet::process_cl_option(const std::string &s)
     }
   }
 
-  for(std::size_t j=0; ms_cl_prefixes[j]!=NULL; j++)
+  for(std::size_t j=0; ms_cl_prefixes[j]!=nullptr; j++)
   {
     std::string ms_cl_prefix=ms_cl_prefixes[j];
 
diff --git a/src/goto-instrument/dump_c.cpp b/src/goto-instrument/dump_c.cpp
index efa0ac4afc2..1020d2021a1 100644
--- a/src/goto-instrument/dump_c.cpp
+++ b/src/goto-instrument/dump_c.cpp
@@ -1309,7 +1309,7 @@ static bool find_block_position_rec(
   if(!root.has_operands())
     return false;
 
-  code_blockt *our_dest=0;
+  code_blockt *our_dest=nullptr;
 
   exprt::operandst &operands=root.operands();
   exprt::operandst::iterator first_found=operands.end();
@@ -1400,14 +1400,14 @@ void dump_ct::insert_local_static_decls(
     std::list<irep_idt> redundant;
     cleanup_decl(d, redundant, type_decls);
 
-    code_blockt *dest_ptr=0;
+    code_blockt *dest_ptr=nullptr;
     exprt::operandst::iterator before=b.operands().end();
 
     // some use of static variables might be optimised out if it is
     // within an if(false) { ... } block
     if(find_block_position_rec(*it, b, dest_ptr, before))
     {
-      CHECK_RETURN(dest_ptr!=0);
+      CHECK_RETURN(dest_ptr!=nullptr);
       dest_ptr->operands().insert(before, d);
     }
   }
@@ -1437,14 +1437,14 @@ void dump_ct::insert_local_type_decls(
     // another hack to ensure symbols inside types are seen
     skip.type()=type;
 
-    code_blockt *dest_ptr=0;
+    code_blockt *dest_ptr=nullptr;
     exprt::operandst::iterator before=b.operands().end();
 
     // we might not find it in case a transparent union type cast
     // has been removed by cleanup operations
     if(find_block_position_rec(*it, b, dest_ptr, before))
     {
-      CHECK_RETURN(dest_ptr!=0);
+      CHECK_RETURN(dest_ptr!=nullptr);
       dest_ptr->operands().insert(before, skip);
     }
   }
diff --git a/src/goto-instrument/model_argc_argv.cpp b/src/goto-instrument/model_argc_argv.cpp
index bae8010d907..7e01d66e62a 100644
--- a/src/goto-instrument/model_argc_argv.cpp
+++ b/src/goto-instrument/model_argc_argv.cpp
@@ -38,7 +38,7 @@ bool model_argc_argv(
   messaget message(message_handler);
   const namespacet ns(symbol_table);
 
-  const symbolt *init_symbol=0;
+  const symbolt *init_symbol=nullptr;
   if(ns.lookup(CPROVER_PREFIX "initialize", init_symbol))
   {
     message.error() << "Linking not done, missing "
diff --git a/src/goto-instrument/wmm/cycle_collection.cpp b/src/goto-instrument/wmm/cycle_collection.cpp
index caef3e7ee77..64b619c4369 100644
--- a/src/goto-instrument/wmm/cycle_collection.cpp
+++ b/src/goto-instrument/wmm/cycle_collection.cpp
@@ -56,7 +56,7 @@ void event_grapht::graph_explorert::collect_cycles(
   for(std::size_t i=0; i<egraph.size(); i++)
     mark[i]=false;
 
-  std::list<event_idt>* order=0;
+  std::list<event_idt>* order=nullptr;
   /* on Power, rfe pairs are also potentially unsafe */
   switch(model)
   {
diff --git a/src/goto-instrument/wmm/goto2graph.cpp b/src/goto-instrument/wmm/goto2graph.cpp
index 7828ac8008a..011ef1a36ac 100644
--- a/src/goto-instrument/wmm/goto2graph.cpp
+++ b/src/goto-instrument/wmm/goto2graph.cpp
@@ -1198,7 +1198,7 @@ bool instrumentert::is_cfg_spurious(const event_grapht::critical_cyclet &cyc)
     const source_locationt &current_location=current_event.source_location;
 
     /* select relevant thread (po) -- or function contained in this thread */
-    goto_programt *current_po=0;
+    goto_programt *current_po=nullptr;
     bool thread_found=false;
 
     Forall_goto_functions(f_it, goto_functions)
diff --git a/src/goto-programs/initialize_goto_model.cpp b/src/goto-programs/initialize_goto_model.cpp
index d284bc403c9..eb2b6f8490b 100644
--- a/src/goto-programs/initialize_goto_model.cpp
+++ b/src/goto-programs/initialize_goto_model.cpp
@@ -81,7 +81,7 @@ bool initialize_goto_model(
         lf.filename=filename;
         lf.language=get_language_from_filename(filename);
 
-        if(lf.language==NULL)
+        if(lf.language==nullptr)
         {
           source_locationt location;
           location.set_file(filename);
diff --git a/src/goto-programs/interpreter.cpp b/src/goto-programs/interpreter.cpp
index a79910b7654..817d04c3a59 100644
--- a/src/goto-programs/interpreter.cpp
+++ b/src/goto-programs/interpreter.cpp
@@ -70,7 +70,7 @@ void interpretert::command()
 {
   #define BUFSIZE 100
   char command[BUFSIZE];
-  if(fgets(command, BUFSIZE-1, stdin)==NULL)
+  if(fgets(command, BUFSIZE-1, stdin)==nullptr)
   {
     done=true;
     return;
diff --git a/src/goto-programs/show_symbol_table.cpp b/src/goto-programs/show_symbol_table.cpp
index 1d5ce87f5a6..6a15759f11e 100644
--- a/src/goto-programs/show_symbol_table.cpp
+++ b/src/goto-programs/show_symbol_table.cpp
@@ -48,7 +48,7 @@ void show_symbol_table_plain(
     else
     {
       ptr=get_language_from_mode(symbol.mode);
-      if(ptr==NULL)
+      if(ptr==nullptr)
         throw "symbol "+id2string(symbol.name)+" has unknown mode";
     }
 
diff --git a/src/goto-symex/goto_symex_state.cpp b/src/goto-symex/goto_symex_state.cpp
index 6fdf4b54aa8..6402923c4cf 100644
--- a/src/goto-symex/goto_symex_state.cpp
+++ b/src/goto-symex/goto_symex_state.cpp
@@ -15,6 +15,7 @@ Author: Daniel Kroening, kroening@kroening.com
 #include <cassert>
 #include <iostream>
 
+#include <util/base_exceptions.h>
 #include <util/std_expr.h>
 #include <util/prefix.h>
 
@@ -22,10 +23,10 @@ Author: Daniel Kroening, kroening@kroening.com
 
 goto_symex_statet::goto_symex_statet():
   depth(0),
-  symex_target(NULL),
+  symex_target(nullptr),
   atomic_section_id(0),
   record_events(true),
-  dirty(0)
+  dirty(nullptr)
 {
   threads.resize(1);
   new_frame();
@@ -541,7 +542,7 @@ bool goto_symex_statet::l2_thread_read_encoding(
     return false;
 
   // is it a shared object?
-  assert(dirty!=0);
+  INVARIANT_STRUCTURED(dirty!=nullptr, nullptr_exceptiont, "dirty is null");
   const irep_idt &obj_identifier=expr.get_object_name();
   if(obj_identifier=="goto_symex::\\guard" ||
      (!ns.lookup(obj_identifier).is_shared() &&
@@ -666,7 +667,8 @@ bool goto_symex_statet::l2_thread_read_encoding(
   expr=ssa_l1;
 
   // and record that
-  assert(symex_target!=NULL);
+  INVARIANT_STRUCTURED(
+    symex_target!=nullptr, nullptr_exceptiont, "symex_target is null");
   symex_target->shared_read(
     guard.as_expr(),
     expr,
@@ -685,7 +687,7 @@ bool goto_symex_statet::l2_thread_write_encoding(
     return false;
 
   // is it a shared object?
-  assert(dirty!=0);
+  INVARIANT_STRUCTURED(dirty!=nullptr, nullptr_exceptiont, "dirty is null");
   const irep_idt &obj_identifier=expr.get_object_name();
   if(obj_identifier=="goto_symex::\\guard" ||
      (!ns.lookup(obj_identifier).is_shared() &&
diff --git a/src/goto-symex/slice_by_trace.cpp b/src/goto-symex/slice_by_trace.cpp
index 80acfa4add8..828b457caa0 100644
--- a/src/goto-symex/slice_by_trace.cpp
+++ b/src/goto-symex/slice_by_trace.cpp
@@ -187,9 +187,9 @@ void symex_slice_by_tracet::parse_events(std::string read_line)
 {
   if(read_line=="")
     return;
-  bool parity=strstr(read_line.c_str(), "!")==NULL;
-  bool universe=strstr(read_line.c_str(), "?")!=NULL;
-  bool has_values=strstr(read_line.c_str(), " ")!=NULL;
+  bool parity=strstr(read_line.c_str(), "!")==nullptr;
+  bool universe=strstr(read_line.c_str(), "?")!=nullptr;
+  bool has_values=strstr(read_line.c_str(), " ")!=nullptr;
   std::cout << "Trace: " << read_line << '\n';
   std::vector<irep_idt> value_v;
   if(has_values)
diff --git a/src/goto-symex/symex_dereference_state.cpp b/src/goto-symex/symex_dereference_state.cpp
index f0e36f5d03c..9911ba51e7d 100644
--- a/src/goto-symex/symex_dereference_state.cpp
+++ b/src/goto-symex/symex_dereference_state.cpp
@@ -43,7 +43,7 @@ bool symex_dereference_statet::has_failed_symbol(
         !ns.lookup(failed_symbol, symbol))
     {
       symbolt sym=*symbol;
-      symbolt *sym_ptr=0;
+      symbolt *sym_ptr=nullptr;
       symbol_exprt sym_expr=sym.symbol_expr();
       state.rename(sym_expr, ns, goto_symex_statet::L1);
       sym.name=to_ssa_expr(sym_expr).get_identifier();
@@ -64,7 +64,7 @@ bool symex_dereference_statet::has_failed_symbol(
         !ns.lookup(failed_symbol, symbol))
     {
       symbolt sym=*symbol;
-      symbolt *sym_ptr=0;
+      symbolt *sym_ptr=nullptr;
       symbol_exprt sym_expr=sym.symbol_expr();
       state.rename(sym_expr, ns, goto_symex_statet::L1);
       sym.name=to_ssa_expr(sym_expr).get_identifier();
diff --git a/src/goto-symex/symex_function_call.cpp b/src/goto-symex/symex_function_call.cpp
index a71a142b89b..06d519e4941 100644
--- a/src/goto-symex/symex_function_call.cpp
+++ b/src/goto-symex/symex_function_call.cpp
@@ -139,7 +139,7 @@ void goto_symext::parameter_assignments(
   {
     // These are va_arg arguments; their types may differ from call to call
     unsigned va_count=0;
-    const symbolt *va_sym=0;
+    const symbolt *va_sym=nullptr;
     while(!ns.lookup(
         id2string(function_identifier)+"::va_arg"+std::to_string(va_count),
         va_sym))
diff --git a/src/goto-symex/symex_main.cpp b/src/goto-symex/symex_main.cpp
index b8a1e294f10..4fce789ad3a 100644
--- a/src/goto-symex/symex_main.cpp
+++ b/src/goto-symex/symex_main.cpp
@@ -158,7 +158,7 @@ void goto_symext::operator()(
   }
 
   delete state.dirty;
-  state.dirty=0;
+  state.dirty=nullptr;
 }
 
 /// symex starting from given program
diff --git a/src/java_bytecode/java_bytecode_convert_method.cpp b/src/java_bytecode/java_bytecode_convert_method.cpp
index 8a02f4f8855..5c2135e8afe 100644
--- a/src/java_bytecode/java_bytecode_convert_method.cpp
+++ b/src/java_bytecode/java_bytecode_convert_method.cpp
@@ -406,7 +406,7 @@ void java_bytecode_convert_methodt::convert(
 const bytecode_infot &java_bytecode_convert_methodt::get_bytecode_info(
   const irep_idt &statement)
 {
-  for(const bytecode_infot *p=bytecode_info; p->mnemonic!=0; p++)
+  for(const bytecode_infot *p=bytecode_info; p->mnemonic!=nullptr; p++)
     if(statement==p->mnemonic)
       return *p;
 
diff --git a/src/java_bytecode/java_bytecode_parser.cpp b/src/java_bytecode/java_bytecode_parser.cpp
index 77874da4944..d24141b76da 100644
--- a/src/java_bytecode/java_bytecode_parser.cpp
+++ b/src/java_bytecode/java_bytecode_parser.cpp
@@ -99,7 +99,7 @@ class java_bytecode_parsert:public parsert
   {
     // pre-hash the mnemonics, so we do this only once
     bytecodes.resize(256);
-    for(const bytecode_infot *p=bytecode_info; p->mnemonic!=0; p++)
+    for(const bytecode_infot *p=bytecode_info; p->mnemonic!=nullptr; p++)
     {
       assert(p->opcode<bytecodes.size());
       bytecodes[p->opcode].mnemonic=p->mnemonic;
diff --git a/src/java_bytecode/java_local_variable_table.cpp b/src/java_bytecode/java_local_variable_table.cpp
index 052b958d058..94d5062fb24 100644
--- a/src/java_bytecode/java_local_variable_table.cpp
+++ b/src/java_bytecode/java_local_variable_table.cpp
@@ -288,7 +288,7 @@ static void populate_predecessor_map(
         auto pred_var=
           (pred<live_variable_at_address.size() ?
            live_variable_at_address[pred] :
-           0);
+           nullptr);
         if(pred_var==&*it)
         {
           // Flow from within same live range?
diff --git a/src/langapi/language_ui.cpp b/src/langapi/language_ui.cpp
index ddd774f2c4b..6897fe01fa2 100644
--- a/src/langapi/language_ui.cpp
+++ b/src/langapi/language_ui.cpp
@@ -68,7 +68,7 @@ bool language_uit::parse(const std::string &filename)
   lf.filename=filename;
   lf.language=get_language_from_filename(filename);
 
-  if(lf.language==NULL)
+  if(lf.language==nullptr)
   {
     source_locationt location;
     location.set_file(filename);
@@ -172,7 +172,7 @@ void language_uit::show_symbol_table_plain(
     else
     {
       ptr=get_language_from_mode(symbol.mode);
-      if(ptr==NULL)
+      if(ptr==nullptr)
         throw "symbol "+id2string(symbol.name)+" has unknown mode";
     }
 
diff --git a/src/langapi/language_util.cpp b/src/langapi/language_util.cpp
index dd31f122ea5..a919f6c816f 100644
--- a/src/langapi/language_util.cpp
+++ b/src/langapi/language_util.cpp
@@ -30,7 +30,7 @@ static languaget* get_language(
 
   languaget *ptr=get_language_from_mode(symbol->mode);
 
-  if(ptr==NULL)
+  if(ptr==nullptr)
     throw "symbol `"+id2string(symbol->name)+
       "' has unknown mode '"+id2string(symbol->mode)+"'";
 
diff --git a/src/langapi/mode.cpp b/src/langapi/mode.cpp
index 55c533f9495..2c3a852b73a 100644
--- a/src/langapi/mode.cpp
+++ b/src/langapi/mode.cpp
@@ -45,7 +45,7 @@ languaget *get_language_from_mode(const irep_idt &mode)
     if(mode==it->mode)
       return it->factory();
 
-  return NULL;
+  return nullptr;
 }
 
 languaget *get_language_from_filename(const std::string &filename)
@@ -53,13 +53,13 @@ languaget *get_language_from_filename(const std::string &filename)
   std::size_t ext_pos=filename.rfind('.');
 
   if(ext_pos==std::string::npos)
-    return NULL;
+    return nullptr;
 
   std::string extension=
     std::string(filename, ext_pos+1, std::string::npos);
 
   if(extension=="")
-    return NULL;
+    return nullptr;
 
   for(languagest::const_iterator
       l_it=languages.begin();
@@ -79,7 +79,7 @@ languaget *get_language_from_filename(const std::string &filename)
     #endif
   }
 
-  return NULL;
+  return nullptr;
 }
 
 languaget *get_default_language()
diff --git a/src/path-symex/path_symex_history.h b/src/path-symex/path_symex_history.h
index 4371e5e26d3..0783281c703 100644
--- a/src/path-symex/path_symex_history.h
+++ b/src/path-symex/path_symex_history.h
@@ -15,6 +15,7 @@ Author: Daniel Kroening, kroening@kroening.com
 #include <cassert>
 #include <limits>
 
+#include <util/base_exceptions.h>
 #include <util/std_expr.h>
 
 #include "loc_ref.h"
@@ -35,7 +36,7 @@ class path_symex_step_reft
   }
 
   path_symex_step_reft():
-    index(std::numeric_limits<std::size_t>::max()), history(0)
+    index(std::numeric_limits<std::size_t>::max()), history(nullptr)
   {
   }
 
@@ -46,7 +47,8 @@ class path_symex_step_reft
 
   path_symex_historyt &get_history() const
   {
-    assert(history!=0);
+    INVARIANT_STRUCTURED(
+      history!=nullptr, nullptr_exceptiont, "history is null");
     return *history;
   }
 
@@ -154,7 +156,8 @@ class path_symex_historyt
 
 inline void path_symex_step_reft::generate_successor()
 {
-  assert(history!=0);
+  INVARIANT_STRUCTURED(
+    history!=nullptr, nullptr_exceptiont, "history is null");
   path_symex_step_reft old=*this;
   index=history->step_container.size();
   history->step_container.push_back(path_symex_stept());
@@ -169,7 +172,8 @@ inline path_symex_step_reft &path_symex_step_reft::operator--()
 
 inline path_symex_stept &path_symex_step_reft::get() const
 {
-  assert(history!=0);
+  INVARIANT_STRUCTURED(
+    history!=nullptr, nullptr_exceptiont, "history is null");
   assert(!is_nil());
   return history->step_container[index];
 }
diff --git a/src/path-symex/path_symex_state_read.cpp b/src/path-symex/path_symex_state_read.cpp
index a6993c19b05..87dea21be4a 100644
--- a/src/path-symex/path_symex_state_read.cpp
+++ b/src/path-symex/path_symex_state_read.cpp
@@ -430,7 +430,7 @@ bool path_symex_statet::is_symbol_member_index(const exprt &src) const
   // the loop avoids recursion
   while(true)
   {
-    const exprt *next=0;
+    const exprt *next=nullptr;
 
     if(current->id()==ID_symbol)
     {
@@ -465,7 +465,7 @@ bool path_symex_statet::is_symbol_member_index(const exprt &src) const
       return false;
 
     // next round
-    assert(next!=0);
+    INVARIANT_STRUCTURED(next!=nullptr, nullptr_exceptiont, "next is null");
     current=next;
   }
 }
diff --git a/src/path-symex/var_map.cpp b/src/path-symex/var_map.cpp
index f5dea20a96d..96d079c48ff 100644
--- a/src/path-symex/var_map.cpp
+++ b/src/path-symex/var_map.cpp
@@ -84,7 +84,7 @@ void var_mapt::init(var_infot &var_info)
     }
     else
     {
-      const symbolt *symbol=0;
+      const symbolt *symbol=nullptr;
       if(ns.lookup(var_info.symbol, symbol))
         throw "var_mapt::init identifier \""
           +id2string(var_info.full_identifier)
diff --git a/src/pointer-analysis/value_set_fi.cpp b/src/pointer-analysis/value_set_fi.cpp
index 77962a3b3b2..d08694b82da 100644
--- a/src/pointer-analysis/value_set_fi.cpp
+++ b/src/pointer-analysis/value_set_fi.cpp
@@ -550,18 +550,18 @@ void value_set_fit::get_value_set_rec(
     if(expr.type().id()==ID_pointer)
     {
       // find the pointer operand
-      const exprt *ptr_operand=NULL;
+      const exprt *ptr_operand=nullptr;
 
       forall_operands(it, expr)
         if(it->type().id()==ID_pointer)
         {
-          if(ptr_operand==NULL)
+          if(ptr_operand==nullptr)
             ptr_operand=&(*it);
           else
             throw "more than one pointer operand in pointer arithmetic";
         }
 
-      if(ptr_operand==NULL)
+      if(ptr_operand==nullptr)
         throw "pointer type sum expected to have pointer operand";
 
       object_mapt pointer_expr_set;
diff --git a/src/pointer-analysis/value_set_fivr.cpp b/src/pointer-analysis/value_set_fivr.cpp
index 6bd7e1321e9..3ea5ef1aa8e 100644
--- a/src/pointer-analysis/value_set_fivr.cpp
+++ b/src/pointer-analysis/value_set_fivr.cpp
@@ -668,18 +668,18 @@ void value_set_fivrt::get_value_set_rec(
     if(expr.type().id()==ID_pointer)
     {
       // find the pointer operand
-      const exprt *ptr_operand=NULL;
+      const exprt *ptr_operand=nullptr;
 
       forall_operands(it, expr)
         if(it->type().id()==ID_pointer)
         {
-          if(ptr_operand==NULL)
+          if(ptr_operand==nullptr)
             ptr_operand=&(*it);
           else
             throw "more than one pointer operand in pointer arithmetic";
         }
 
-      if(ptr_operand==NULL)
+      if(ptr_operand==nullptr)
         throw "pointer type sum expected to have pointer operand";
 
       object_mapt pointer_expr_set;
diff --git a/src/pointer-analysis/value_set_fivrns.cpp b/src/pointer-analysis/value_set_fivrns.cpp
index 0eaf08b201b..3b5ce55a3aa 100644
--- a/src/pointer-analysis/value_set_fivrns.cpp
+++ b/src/pointer-analysis/value_set_fivrns.cpp
@@ -454,18 +454,18 @@ void value_set_fivrnst::get_value_set_rec(
     if(expr.type().id()==ID_pointer)
     {
       // find the pointer operand
-      const exprt *ptr_operand=NULL;
+      const exprt *ptr_operand=nullptr;
 
       forall_operands(it, expr)
         if(it->type().id()==ID_pointer)
         {
-          if(ptr_operand==NULL)
+          if(ptr_operand==nullptr)
             ptr_operand=&(*it);
           else
             throw "more than one pointer operand in pointer arithmetic";
         }
 
-      if(ptr_operand==NULL)
+      if(ptr_operand==nullptr)
         throw "pointer type sum expected to have pointer operand";
 
       object_mapt pointer_expr_set;
diff --git a/src/solvers/miniBDD/miniBDD.h b/src/solvers/miniBDD/miniBDD.h
index f7dde020fe6..9b994b88ff6 100644
--- a/src/solvers/miniBDD/miniBDD.h
+++ b/src/solvers/miniBDD/miniBDD.h
@@ -55,7 +55,7 @@ class mini_bddt
   unsigned node_number() const;
   void clear();
 
-  bool is_initialized() const { return node!=0; }
+  bool is_initialized() const { return node!=nullptr; }
 
   // internal
   explicit mini_bddt(class mini_bdd_nodet *_node);
diff --git a/src/solvers/miniBDD/miniBDD.inc b/src/solvers/miniBDD/miniBDD.inc
index 091725ed333..a2077ab95f1 100644
--- a/src/solvers/miniBDD/miniBDD.inc
+++ b/src/solvers/miniBDD/miniBDD.inc
@@ -2,7 +2,7 @@
 
 // inline functions
 
-inline mini_bddt::mini_bddt():node(0)
+inline mini_bddt::mini_bddt():node(nullptr)
 {
 }
 
@@ -82,7 +82,7 @@ inline void mini_bddt::clear()
   if(is_initialized())
   {
     node->remove_reference();
-    node=NULL;
+    node=nullptr;
   }
 }
 
diff --git a/src/solvers/sat/pbs_dimacs_cnf.cpp b/src/solvers/sat/pbs_dimacs_cnf.cpp
index 731c6ac7ae6..69e4c78a290 100644
--- a/src/solvers/sat/pbs_dimacs_cnf.cpp
+++ b/src/solvers/sat/pbs_dimacs_cnf.cpp
@@ -125,7 +125,7 @@ bool pbs_dimacs_cnft::pbs_solve()
     {
       std::getline(file, line);
       if(strstr(line.c_str(),
-                "Variable Assignments Satisfying CNF Formula:")!=NULL)
+                "Variable Assignments Satisfying CNF Formula:")!=nullptr)
         {
           // print ("Reading assignments...\n");
           // std::cout << "No literals: " << no_variables() << "\n";
@@ -143,12 +143,12 @@ bool pbs_dimacs_cnft::pbs_solve()
           // std::cout << "\n";
           // print ("Finished reading assignments.\n");
         }
-      else if(strstr(line.c_str(), "SAT... SUM")!=NULL)
+      else if(strstr(line.c_str(), "SAT... SUM")!=nullptr)
         {
           // print (line);
           sscanf(line.c_str(), "%*s %*s %*s %d", &opt_sum);
         }
-      else if(strstr(line.c_str(), "SAT - All implied")!=NULL)
+      else if(strstr(line.c_str(), "SAT - All implied")!=nullptr)
         {
           // print (line);
           sscanf(
@@ -156,15 +156,15 @@ bool pbs_dimacs_cnft::pbs_solve()
             "%*s %*s %*s %*s %*s %*s %*s %*s %*s %*s %*s %d",
             &opt_sum);
         }
-      else if(strstr(line.c_str(), "SAT... Solution")!=NULL)
+      else if(strstr(line.c_str(), "SAT... Solution")!=nullptr)
         {
           // print(line);
           sscanf(line.c_str(), "%*s %*s %*s %d", &opt_sum);
         }
-      else if(strstr(line.c_str(), "Optimal Soln")!=NULL)
+      else if(strstr(line.c_str(), "Optimal Soln")!=nullptr)
         {
           // print(line);
-          if(strstr(line.c_str(), "time out")!=NULL)
+          if(strstr(line.c_str(), "time out")!=nullptr)
             {
               status() << "WARNING:  TIMED OUT.  SOLUTION MAY BE INCORRECT."
                        << eom;
diff --git a/src/util/base_exceptions.h b/src/util/base_exceptions.h
new file mode 100644
index 00000000000..6d1218a9e7c
--- /dev/null
+++ b/src/util/base_exceptions.h
@@ -0,0 +1,37 @@
+/*******************************************************************\
+
+Module: Util base exceptions
+
+Author: Diffblue Ltd.
+
+\*******************************************************************/
+
+/// \file
+/// Generic exception types primarily designed for use with invariants.
+
+#ifndef CPROVER_UTIL_BASE_EXCEPTIONS_H
+#define CPROVER_UTIL_BASE_EXCEPTIONS_H
+
+#include "util/invariant.h"
+
+class bad_cast_exceptiont:public invariant_failedt
+{
+public:
+  // Normally we'd prefer
+  // using invariant_failedt::invariant_failedt;
+  // However, this isn't supported on VS2013.
+
+  template <typename... Ts>
+  explicit bad_cast_exceptiont(Ts &&...ts):
+    invariant_failedt(std::forward<Ts>(ts)...) {}
+};
+
+class nullptr_exceptiont:public invariant_failedt
+{
+public:
+  template <typename... Ts>
+  explicit nullptr_exceptiont(Ts &&...ts):
+    invariant_failedt(std::forward<Ts>(ts)...) {}
+};
+
+#endif
diff --git a/src/util/config.cpp b/src/util/config.cpp
index ee24ab7b0f7..a256ff6b17e 100644
--- a/src/util/config.cpp
+++ b/src/util/config.cpp
@@ -739,7 +739,7 @@ bool configt::set(const cmdlinet &cmdline)
   ansi_c.arch="none";
   ansi_c.lib=configt::ansi_ct::libt::LIB_NONE;
   // NOLINTNEXTLINE(readability/casting)
-  ansi_c.NULL_is_zero=reinterpret_cast<size_t>((void*)0)==0;
+  ansi_c.NULL_is_zero=reinterpret_cast<size_t>(nullptr)==0;
 
   // Default is ROUND_TO_EVEN, justified by C99:
   // 1 At program startup the floating-point environment is initialized as
@@ -773,7 +773,7 @@ bool configt::set(const cmdlinet &cmdline)
   {
     // environment variable set?
     const char *CLASSPATH=getenv("CLASSPATH");
-    if(CLASSPATH!=NULL)
+    if(CLASSPATH!=nullptr)
       set_classpath(CLASSPATH);
     else
       set_classpath("."); // default
diff --git a/src/util/file_util.cpp b/src/util/file_util.cpp
index 3753fa5aab8..37dfd595876 100644
--- a/src/util/file_util.cpp
+++ b/src/util/file_util.cpp
@@ -51,7 +51,7 @@ std::string get_current_working_directory()
 
   errno=0;
 
-  while(buf && getcwd(buf, bsize-1)==NULL && errno==ERANGE)
+  while(buf && getcwd(buf, bsize-1)==nullptr && errno==ERANGE)
   {
     bsize*=2;
     buf=reinterpret_cast<char*>(realloc(buf, sizeof(char)*bsize));
@@ -98,10 +98,10 @@ void delete_directory(const std::string &path)
   delete_directory_utf16(utf8_to_utf16_little_endian(path));
 #else
   DIR *dir=opendir(path.c_str());
-  if(dir!=NULL)
+  if(dir!=nullptr)
   {
     struct dirent *ent;
-    while((ent=readdir(dir))!=NULL)
+    while((ent=readdir(dir))!=nullptr)
     {
       // Needed for Alpine Linux
       if(strcmp(ent->d_name, ".")==0 || strcmp(ent->d_name, "..")==0)
diff --git a/src/util/invariant.cpp b/src/util/invariant.cpp
index eb63382ef76..d3f750041a3 100644
--- a/src/util/invariant.cpp
+++ b/src/util/invariant.cpp
@@ -54,7 +54,7 @@ static bool output_demangled_name(
 
     int demangle_success=1;
     char *demangled=
-      abi::__cxa_demangle(mangled.c_str(), NULL, 0, &demangle_success);
+      abi::__cxa_demangle(mangled.c_str(), nullptr, nullptr, &demangle_success);
 
     if(demangle_success==0)
     {
diff --git a/src/util/irep_ids.cpp b/src/util/irep_ids.cpp
index 8aff81777ae..50e0f537fa5 100644
--- a/src/util/irep_ids.cpp
+++ b/src/util/irep_ids.cpp
@@ -22,7 +22,7 @@ const char *irep_ids_table[]=
 
 #include "irep_ids.def"
 
-  NULL,
+  nullptr,
 };
 
 #ifdef USE_DSTRING
@@ -47,7 +47,7 @@ void initialize_string_container()
 {
   // this is called by the constructor of string_containert
 
-  for(unsigned i=0; irep_ids_table[i]!=NULL; i++)
+  for(unsigned i=0; irep_ids_table[i]!=nullptr; i++)
   {
     unsigned x;
     x=string_container[irep_ids_table[i]];
diff --git a/src/util/language_file.cpp b/src/util/language_file.cpp
index 2aa57a85c6a..7ca179f68fe 100644
--- a/src/util/language_file.cpp
+++ b/src/util/language_file.cpp
@@ -14,14 +14,14 @@ Author: Daniel Kroening, kroening@kroening.com
 
 language_filet::language_filet(const language_filet &rhs):
   modules(rhs.modules),
-  language(rhs.language==NULL?NULL:rhs.language->new_language()),
+  language(rhs.language==nullptr?nullptr:rhs.language->new_language()),
   filename(rhs.filename)
 {
 }
 
 language_filet::~language_filet()
 {
-  if(language!=NULL)
+  if(language!=nullptr)
     delete language;
 }
 
diff --git a/src/util/language_file.h b/src/util/language_file.h
index e2e8750be5d..a18d4685a39 100644
--- a/src/util/language_file.h
+++ b/src/util/language_file.h
@@ -49,7 +49,7 @@ class language_filet
 
   language_filet(const language_filet &rhs);
 
-  language_filet():language(NULL)
+  language_filet():language(nullptr)
   {
   }
 
diff --git a/src/util/message.h b/src/util/message.h
index 41c91174001..c3d73d5f4d2 100644
--- a/src/util/message.h
+++ b/src/util/message.h
@@ -133,7 +133,7 @@ class messaget
   // constructors, destructor
 
   messaget():
-    message_handler(NULL),
+    message_handler(nullptr),
     mstream(M_DEBUG, *this)
   {
   }
diff --git a/src/util/namespace.cpp b/src/util/namespace.cpp
index 50de95f2961..218e73d2850 100644
--- a/src/util/namespace.cpp
+++ b/src/util/namespace.cpp
@@ -127,10 +127,10 @@ unsigned namespacet::get_max(const std::string &prefix) const
 {
   unsigned m=0;
 
-  if(symbol_table1!=NULL)
+  if(symbol_table1!=nullptr)
     m=std::max(m, ::get_max(prefix, symbol_table1->symbols));
 
-  if(symbol_table2!=NULL)
+  if(symbol_table2!=nullptr)
     m=std::max(m, ::get_max(prefix, symbol_table2->symbols));
 
   return m;
@@ -142,7 +142,7 @@ bool namespacet::lookup(
 {
   symbol_tablet::symbolst::const_iterator it;
 
-  if(symbol_table1!=NULL)
+  if(symbol_table1!=nullptr)
   {
     it=symbol_table1->symbols.find(name);
 
@@ -153,7 +153,7 @@ bool namespacet::lookup(
     }
   }
 
-  if(symbol_table2!=NULL)
+  if(symbol_table2!=nullptr)
   {
     it=symbol_table2->symbols.find(name);
 
diff --git a/src/util/namespace.h b/src/util/namespace.h
index ea6b33cfdbd..a3b9f3827c6 100644
--- a/src/util/namespace.h
+++ b/src/util/namespace.h
@@ -64,7 +64,7 @@ class namespacet:public namespace_baset
 public:
   // constructors
   explicit namespacet(const symbol_tablet &_symbol_table)
-  { symbol_table1=&_symbol_table; symbol_table2=NULL; }
+  { symbol_table1=&_symbol_table; symbol_table2=nullptr; }
 
   namespacet(
     const symbol_tablet &_symbol_table1,
@@ -101,12 +101,12 @@ class multi_namespacet:public namespacet
 {
 public:
   // constructors
-  multi_namespacet():namespacet(NULL, NULL)
+  multi_namespacet():namespacet(nullptr, nullptr)
   {
   }
 
   explicit multi_namespacet(
-    const symbol_tablet &symbol_table):namespacet(NULL, NULL)
+    const symbol_tablet &symbol_table):namespacet(nullptr, nullptr)
   {
     add(symbol_table);
   }
diff --git a/src/util/parser.h b/src/util/parser.h
index b450de7f614..bf572e6004d 100644
--- a/src/util/parser.h
+++ b/src/util/parser.h
@@ -39,7 +39,7 @@ class parsert:public messaget
     last_line.clear();
   }
 
-  parsert():in(NULL) { clear(); }
+  parsert():in(nullptr) { clear(); }
   virtual ~parsert() { }
 
   // The following are for the benefit of the scanner
diff --git a/src/util/pipe_stream.cpp b/src/util/pipe_stream.cpp
index 4306bce8e00..44ac29b3eb4 100644
--- a/src/util/pipe_stream.cpp
+++ b/src/util/pipe_stream.cpp
@@ -159,12 +159,12 @@ int pipe_streamt::run()
         a_it++, i++)
        _argv[i]=strdup(a_it->c_str());
 
-    _argv[args.size()+1]=NULL;
+    _argv[args.size()+1]=nullptr;
 
     int result=execvp(executable.c_str(), _argv);
 
     if(result==-1)
-      perror(0);
+      perror(nullptr);
 
     return result;
   }
@@ -289,7 +289,7 @@ std::streamsize filedescriptor_streambuft::xsputn(
 /// read a character from the piped process
 std::streambuf::int_type filedescriptor_streambuft::underflow()
 {
-  if(gptr()==0)
+  if(gptr()==nullptr)
     return traits_type::eof();
 
   if(gptr()<egptr())
@@ -339,7 +339,7 @@ std::streamsize filedescriptor_streambuft::xsgetn(
 /// determine number of available characters in stream
 std::streamsize filedescriptor_streambuft::showmanyc()
 {
-  if(gptr()==0)
+  if(gptr()==nullptr)
     return 0;
 
   if(gptr()<egptr())
diff --git a/src/util/ref_expr_set.h b/src/util/ref_expr_set.h
index 349619c233f..1ab8ae328a3 100644
--- a/src/util/ref_expr_set.h
+++ b/src/util/ref_expr_set.h
@@ -35,7 +35,7 @@ class ref_expr_sett:public reference_counting<ref_expr_set_dt>
 
   bool empty() const
   {
-    if(d==NULL)
+    if(d==nullptr)
       return true;
     return d->expr_set.empty();
   }
@@ -52,13 +52,13 @@ class ref_expr_sett:public reference_counting<ref_expr_set_dt>
 
   bool make_union(const ref_expr_sett &s2)
   {
-    if(s2.d==NULL)
+    if(s2.d==nullptr)
       return false;
 
     if(s2.d==d)
       return false;
 
-    if(d==NULL)
+    if(d==nullptr)
     {
       copy_from(s2);
       return true;
diff --git a/src/util/reference_counting.h b/src/util/reference_counting.h
index ffdc8eed754..4d5accb5ece 100644
--- a/src/util/reference_counting.h
+++ b/src/util/reference_counting.h
@@ -19,7 +19,7 @@ template<typename T>
 class reference_counting
 {
 public:
-  reference_counting():d(NULL)
+  reference_counting():d(nullptr)
   {
   }
 
@@ -31,7 +31,7 @@ class reference_counting
   // copy constructor
   reference_counting(const reference_counting &other):d(other.d)
   {
-    if(d!=NULL)
+    if(d!=nullptr)
     {
       assert(d->ref_count!=0);
       d->ref_count++;
@@ -50,7 +50,7 @@ class reference_counting
   ~reference_counting()
   {
     remove_ref(d);
-    d=NULL;
+    d=nullptr;
   }
 
   void swap(reference_counting &other)
@@ -61,12 +61,12 @@ class reference_counting
   void clear()
   {
     remove_ref(d);
-    d=NULL;
+    d=nullptr;
   }
 
   const T &read() const
   {
-    if(d==NULL)
+    if(d==nullptr)
       return T::blank;
     return *d;
   }
@@ -104,7 +104,7 @@ class reference_counting
 
     remove_ref(d);
     d=other.d;
-    if(d!=NULL)
+    if(d!=nullptr)
       d->ref_count++;
   }
 
@@ -118,7 +118,7 @@ class reference_counting
 template<class T>
 void reference_counting<T>::remove_ref(dt *old_d)
 {
-  if(old_d==NULL)
+  if(old_d==nullptr)
     return;
 
   assert(old_d->ref_count!=0);
@@ -151,7 +151,7 @@ void reference_counting<T>::detatch()
   std::cout << "DETATCH1: " << d << '\n';
   #endif
 
-  if(d==NULL)
+  if(d==nullptr)
   {
     d=new dt;
 
diff --git a/src/util/run.cpp b/src/util/run.cpp
index 164cac834d3..c01aff35bd6 100644
--- a/src/util/run.cpp
+++ b/src/util/run.cpp
@@ -117,13 +117,13 @@ int run(
     {
       // resume signals
       remove_signal_catcher();
-      sigprocmask(SIG_SETMASK, &old_mask, NULL);
+      sigprocmask(SIG_SETMASK, &old_mask, nullptr);
 
       char **_argv=new char * [argv.size()+1];
       for(std::size_t i=0; i<argv.size(); i++)
         _argv[i]=strdup(argv[i].c_str());
 
-      _argv[argv.size()]=NULL;
+      _argv[argv.size()]=nullptr;
 
       if(stdin_fd!=STDIN_FILENO)
         dup2(stdin_fd, STDIN_FILENO);
@@ -137,7 +137,7 @@ int run(
     else /* fork() returns new pid to the parent process */
     {
       // resume signals
-      sigprocmask(SIG_SETMASK, &old_mask, NULL);
+      sigprocmask(SIG_SETMASK, &old_mask, nullptr);
 
       int status;     /* parent process: child's exit status */
 
@@ -166,7 +166,7 @@ int run(
   else /* fork returns -1 on failure */
   {
     // resume signals
-    sigprocmask(SIG_SETMASK, &old_mask, NULL);
+    sigprocmask(SIG_SETMASK, &old_mask, nullptr);
 
     if(stdin_fd!=STDIN_FILENO)
       close(stdin_fd);
diff --git a/src/util/signal_catcher.cpp b/src/util/signal_catcher.cpp
index 168eaa3d5a6..8d25e275e77 100644
--- a/src/util/signal_catcher.cpp
+++ b/src/util/signal_catcher.cpp
@@ -41,7 +41,7 @@ void install_signal_catcher()
   sigfillset(&(act.sa_mask));
 
   // install signal handler
-  sigaction(SIGTERM, &act, NULL);
+  sigaction(SIGTERM, &act, nullptr);
   #endif
 }
 
@@ -57,7 +57,7 @@ void remove_signal_catcher()
   act.sa_flags=0;
   sigfillset(&(act.sa_mask));
 
-  sigaction(SIGTERM, &act, NULL);
+  sigaction(SIGTERM, &act, nullptr);
   #endif
 }
 
diff --git a/src/util/tempdir.cpp b/src/util/tempdir.cpp
index 9133c6232d2..b796befa707 100644
--- a/src/util/tempdir.cpp
+++ b/src/util/tempdir.cpp
@@ -58,7 +58,7 @@ std::string get_temporary_directory(const std::string &name_template)
   #else
     std::string prefixed_name_template="/tmp/";
     const char *TMPDIR_env=getenv("TMPDIR");
-    if(TMPDIR_env!=0)
+    if(TMPDIR_env!=nullptr)
       prefixed_name_template=TMPDIR_env;
     if(*prefixed_name_template.rbegin()!='/')
       prefixed_name_template+='/';
diff --git a/src/util/tempfile.cpp b/src/util/tempfile.cpp
index bbb6c526db1..a9f761fb882 100644
--- a/src/util/tempfile.cpp
+++ b/src/util/tempfile.cpp
@@ -107,7 +107,7 @@ std::string get_temporary_file(
   #else
   std::string dir="/tmp/";
   const char *TMPDIR_env=getenv("TMPDIR");
-  if(TMPDIR_env!=0)
+  if(TMPDIR_env!=nullptr)
     dir=TMPDIR_env;
   if(*dir.rbegin()!='/')
     dir+='/';
diff --git a/src/util/unicode.cpp b/src/util/unicode.cpp
index 60c6e06ff97..df38d52f8e7 100644
--- a/src/util/unicode.cpp
+++ b/src/util/unicode.cpp
@@ -154,12 +154,12 @@ std::string utf32_to_utf8(const std::basic_string<unsigned int> &s)
 
 const char **narrow_argv(int argc, const wchar_t **argv_wide)
 {
-  if(argv_wide==NULL)
-    return NULL;
+  if(argv_wide==nullptr)
+    return nullptr;
 
   // the following never gets deleted
   const char **argv_narrow=new const char *[argc+1];
-  argv_narrow[argc]=0;
+  argv_narrow[argc]=nullptr;
 
   for(int i=0; i<argc; i++)
     argv_narrow[i]=strdup(narrow(argv_wide[i]).c_str());