Macros for Reporting

This topic applies to:

Edition	Visual Basic	C#	F#	C++	Web Developer
Express				Native only
Pro, Premium, and Ultimate				Native only

You can use the _RPTn, and _RPTFn macros, defined in CRTDBG.H, to replace the use of printf statements for debugging. These macros automatically disappear in your release build when _DEBUG is not defined, so there is no need to enclose them in #ifdefs.

Macro	Function
_RPT0, _RPT1, _RPT2, _RPT3, _RPT4	Outputs a message string and zero to four arguments. For _RPT1 through _RPT4, the message string serves as a printf-style formatting string for the arguments.
_RPTF0, _RPTF1, _RPTF2, _RPTF4,	Same as _RPTn , but these macros also output the file name and line number where the macro is located.

Consider the following example:

#ifdef _DEBUG
    if ( someVar > MAX_SOMEVAR )
        printf( "OVERFLOW! In NameOfThisFunc( ),
               someVar=%d, otherVar=%d.\n",
               someVar, otherVar );
#endif

This code outputs the values of someVar and otherVar to stdout. You can use the following call to _RPTF2 to report these same values and, additionally, the file name and line number:

if (someVar > MAX_SOMEVAR) _RPTF2(_CRT_WARN, "In NameOfThisFunc( ), someVar= %d, otherVar= %d\n", someVar, otherVar );

If you find that a particular application needs debug reporting that the macros supplied with the C run-time library do not provide, you can write a macro designed specifically to fit your own requirements. In one of your header files, for example, you could include code like the following to define a macro called ALERT_IF2:

#ifndef _DEBUG                  /* For RELEASE builds */
#define  ALERT_IF2(expr, msg, arg1, arg2)  do {} while (0)
#else                           /* For DEBUG builds   */
#define  ALERT_IF2(expr, msg, arg1, arg2) \
    do { \
        if ((expr) && \
            (1 == _CrtDbgReport(_CRT_ERROR, \
                __FILE__, __LINE__, msg, arg1, arg2))) \
            _CrtDbgBreak( ); \
    } while (0)
#endif

One call to ALERT_IF2 could perform all the functions of the printf code at the start of this topic:

ALERT_IF2(someVar > MAX_SOMEVAR, "OVERFLOW! In NameOfThisFunc( ), 
someVar=%d, otherVar=%d.\n", someVar, otherVar );

Because a custom macro can easily be changed to report more or less information to different destinations (depending on what is more convenient), this approach can be particularly useful as your debugging requirements evolve.

See Also

Other Resources

CRT Debugging Techniques