add file_exists(path) as wrapper for access(path)

This offers the obvious wrapper around the OS-specific access() function, to
be used until we switch to C++17.

Author: Daniel Kroening

src/util/file_util.cpp

@@ -203,3 +203,12 @@ bool create_directory(const std::string &path)
   return mkdir(path.c_str(), 0777) == 0;
 #endif
 }
+
+bool file_exists(const std::string &path)
+{
+#ifdef _WIN32
+  return _waccess(utf8_to_utf16_native_endian(path).c_str(), 0) == 0;
+#else
+  return access(path.c_str(), F_OK) == 0;
+#endif
+}

src/util/file_util.h

@@ -32,4 +32,9 @@ bool is_directory(const std::string &path);
 /// \return true iff the directory was created
 bool create_directory(const std::string &path);
 
+/// Check whether file with given path exists.
+/// C++17 will allow us to use std::filesystem::directory_entry(file).exists()
+/// \return true iff the file exists
+bool file_exists(const std::string &path);
+
 #endif // CPROVER_UTIL_FILE_UTIL_H