Refactor out method for generating a struct expression

The extracted method gives the option for the caller to exclude padding
members (which don't exist in the C code and are generated for GOTO to
provide a more accurate representation of the struct).

Author: thk123

src/ansi-c/expr2c.cpp

@@ -2337,6 +2337,31 @@ Function: expr2ct::convert_struct
 std::string expr2ct::convert_struct(
   const exprt &src,
   unsigned &precedence)
+{
+  return convert_struct(src, precedence, true);
+}
+
+/*******************************************************************\
+
+Function: expr2ct::convert_struct
+
+  Inputs:
+    src - The struct declaration expression
+    precedence
+    include_padding_members - Should the generated C code
+                              include the padding members added
+                              to structs for GOTOs benifit
+
+ Outputs: A string representation of the struct expression
+
+ Purpose: To generate a C-like string representing a struct. Can optionally
+          include the padding parameters.
+
+\*******************************************************************/
+std::string expr2ct::convert_struct(
+  const exprt &src,
+  unsigned &precedence,
+  bool include_padding_members)
 {
   const typet full_type=ns.follow(src.type());
 
@@ -2368,6 +2393,12 @@ std::string expr2ct::convert_struct(
     if(o_it->type().id()==ID_code)
       continue;
 
+    if(c_it->get_is_padding() && !include_padding_members)
+    {
+      ++o_it;
+      continue;
+    }
+
     if(first)
       first=false;
     else

src/ansi-c/expr2c_class.h

@@ -209,6 +209,11 @@ class expr2ct
   std::string convert_designated_initializer(const exprt &src, unsigned &precedence);
   std::string convert_concatenation(const exprt &src, unsigned &precedence);
   std::string convert_sizeof(const exprt &src, unsigned &precedence);
+
+  std::string convert_struct(
+    const exprt &src,
+    unsigned &precedence,
+    bool include_padding_members);
 };
 
 #endif // CPROVER_ANSI_C_EXPR2C_CLASS_H