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Some macros for debugging C++ programs

Abstract

This article describes some preprocessor macros for use with debugging C++ code. This system has been extended to use my non-standard I/O system described in a later article.

1. Another Version of the C/C++ assert Macro

In addition to the standard C/C++ assert macro I have designed a macro called ASSERT which behaves identically to assert except that it is never turned off (even when the symbol NDEBUG is set). Here is the definition of the macro ASSERT:

#define ASSERT(test)                                           \
   do {                                                        \
   if (!(test)) {                                              \
      PRINTF_AND_EXIT((PLEASE_EMAIL_DAVIN                      \
                      "*** Assertion failed at (%s:%d) \n\n"   \
                      "*** TEST: %s\n",                        \
                      __FILE__,                                \
                      __LINE__,                                \
                      #test));                                 \
   }                                                           \
   } while (0)

As can be seen in the above macro definition, this macro makes use of the following two helper macros. Here is the first:

#ifdef NDEBUG
#define PLEASE_EMAIL_DAVIN "Please email davin dot pearson at gmail dot com with the following information:\n\n"
#else /* !NDEBUG */
#define PLEASE_EMAIL_DAVIN "\n\n"
#endif /* NDEBUG */

and here is the second:

#ifdef NDEBUG
#define PRINTF_AND_EXIT(ARGS_LIST) \
  do { set_gfx_mode(GFX_TEXT,0,0,0,0); allegro_message ARGS_LIST; exit(EXIT_FAILURE); } while (0)
#else /* !NDEBUG */
#define PRINTF_AND_EXIT(ARGS_LIST) \
   do { printf ARGS_LIST; BREAKPOINT; exit(EXIT_FAILURE); } while (0)
#endif /* NDEBUG */

As can be seen in the above macro definition, I use and link with the Allegro graphics library, which includes such functions as set_gfx_mode and allegro_message.

2. Two More Debugging Macros Called ASSERT_INFO and assert_info

I have defined a macro called ASSERT_INFO. Here is the definition of the macro:

#define ASSERT_INFO(test,info)                               \
do {                                                         \
   if (!(test)) {                                            \
      PRINTF_AND_EXIT((PLEASE_EMAIL_DAVIN                    \
                       "*** Assertion failed at (%s:%d)\n\n" \
                       "*** INFO: %s\n",                     \
                       __FILE__,                             \
                       __LINE__,                             \
                       string(info).const_char_star()));     \
   }                                                         \
} while (0)

The advantage of this macro over assert and ASSERT is that there is room for debugging information when the assertion fails. The definition of assert_info is straightforward:

#ifdef NDEBUG
#define assert_info(test,info) ASSERT_INFO(test,info)
#else
#define assert_info(test,info)
#endif /* NDEBUG */

3. A Macro Called SHOULD_NEVER_HAPPEN

The following macro is equivalent to the statement ASSERT(false):

#define SHOULD_NEVER_HAPPEN() ASSERT_INFO(false, "This line should not be executed");

4. A Macro Called ERROR

The following macro is equivalent to the statement ASSERT(false), except that (like ASSERT_INFO) it allows for debugging information to be printed when the assertion fails.

#define ERROR(info) ASSERT_INFO(false, info)

The assert_info macro is roughly equivalent to Java Version 1.5's assertion facility.

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