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#include <stdio.h>

int main(void) {
  #if defined(__STDC__)
    #if (__STDC__ == 1)
      printf("Implementation is ISO-conforming.\n");
    #else
      printf("Implementation is not ISO-conforming.\n");
    #endif
  #else   /* !defined(__STDC__) */
    printf("__STDC__ is not defined.\n");
  #endif
  /* ... */
  return 0;
}

Compliant Solution (Test for Optional

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Feature)

This compliant solution tests to see if the C11 predefined macro __STDC_ANALYZABLE__ is defined and what value the implementation has given the macro:

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#if defined(__STDC_LIB_EXT1__)
  #if (__STDC_LIB_EXT1__ >= 201112L)
    #define USE_EXT1 1
    #define __STDC_WANT_LIB_EXT1__ 1 /* Want the ext1 functions */
  #endif
#endif
 
#include <string.h>
#include <stdlib.h>
 
int main(void) {
  char source_msg[] = "This is a test.";
  char *msg = malloc(sizeof(source_msg) + 1);
 
  if (msg != NULL) {
    #if defined(USE_EXT1)
      strcpy_s(msg, sizeof msg, source_msg);
    #else
      strcpy(msg, source_msg);
    #endif
  } 
  else {
    return EXIT_FAILURE;
  }
  return 0;
}

Compliant Solution (Optional Language Features)

The previous compliant solution comes close to violating PRE09-C. Do not replace secure functions with deprecated or obsolescent functions, and would if a function-like macro were defined which called either strcpy_s() or strcpy() depending on if USE_EXT1 were defined.  This compliant solution solves the problem by including a custom library that implements the optional language feature, which in this case is the Safe C Library available from SourceForge.

#if defined(__STDC_LIB_EXT1__)
  #if (__STDC_LIB_EXT1__ >= 201112L)
    #define USE_EXT1 1
    #define __STDC_WANT_LIB_EXT1__ 1 /* Want the ext1 functions */
  #endif
#endif
 
#include <string.h>
#include <stdlib.h>

#if !defined(USE_EXT1)
  #include "safe_str_lib.h"
#endif
  
int main(void) {
  char source_msg[] = "This is a test.";
  char *msg = malloc(sizeof(source_msg) + 1);
 
  if (msg != NULL) {
    strcpy_s(msg, sizeof msg, source_msg);
  } 
  else {
    return EXIT_FAILURE;
  }
  return 0;
}

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