c++ - How do you create a debug only function that takes a variable argument list? Like printf()

Question

I'd like to make a debug logging function with the same parameters as printf. But one that can be removed by the pre-processor during optimized builds.

For example:

Debug_Print("Warning: value %d > 3!
", value);

I've looked at variadic macros but those aren't available on all platforms. gcc supports them, msvc does not.

question from:https://stackoverflow.com/questions/15240/how-do-you-create-a-debug-only-function-that-takes-a-variable-argument-list-lik

Answer 1

I still do it the old way, by defining a macro (XTRACE, below) which correlates to either a no-op or a function call with a variable argument list. Internally, call vsnprintf so you can keep the printf syntax:

#include <stdio.h>

void XTrace0(LPCTSTR lpszText)
{
   ::OutputDebugString(lpszText);
}

void XTrace(LPCTSTR lpszFormat, ...)
{
    va_list args;
    va_start(args, lpszFormat);
    int nBuf;
    TCHAR szBuffer[512]; // get rid of this hard-coded buffer
    nBuf = _vsnprintf(szBuffer, 511, lpszFormat, args);
    ::OutputDebugString(szBuffer);
    va_end(args);
}

Then a typical #ifdef switch:

#ifdef _DEBUG
#define XTRACE XTrace
#else
#define XTRACE
#endif

Well that can be cleaned up quite a bit but it's the basic idea.