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Macros for Reporting

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Applies to: yesVisual Studio noVisual Studio for Mac

Note

This article applies to Visual Studio 2017. If you're looking for the latest Visual Studio documentation, see Visual Studio documentation. We recommend upgrading to the latest version of Visual Studio. Download it here

For debugging, you can use the _RPTn and _RPTFn macros, defined in CRTDBG.H, to replace the use of printf statements. You don't need to inclose them in #ifdefs, because they automatically disappear in your release build when _DEBUG isn't defined.

Macro Description
_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, _RPTF3, _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 );

You might find that a particular application needs debug reporting that the macros supplied with the C run-time library do not provide. For these cases, 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 do all the functions of the printf code:

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

You can easily change a custom macro to report more or less information to different destinations. This approach is particularly useful as your debugging requirements evolve.

See also