Question

I am looking to have a portable debug class since i plan to work on the project on various platforms. This class provides methods to write messages through XDebug.WriteLine(“I like number %d”, 7); Which internally redirects the arguments to the system specific method.

This requires me to pass the ellipsis data as a parameter. And here is the problem. It works on integers, but loses floats on pass through.

XDebug::WriteLine("Print numbers %f, %f",1.234, 3.210f);
XDebug::odprintf(L"Print numbers %f, %f",1.234, 3.210f);

outputs

Print numbers 0.000000, 0.000000
Print numbers 1.234000, 3.210000

I am trying to figure out where the arguments get mangled. Would appreciate your help. The entire debug class is below.

#pragma once
#ifndef _XDEBUG_H_
#define _XDEBUG_H_

#include <stdio.h>
#include <stdarg.h>
#include <ctype.h>
#include <Windows.h>;

class XDebug
{
public:

    static void __cdecl WriteLine(const char* txt, ...){
        #if (CC_TARGET_PLATFORM == CC_PLATFORM_WIN32)

        int stringSize = MultiByteToWideChar (CP_ACP, 0, txt, -1, NULL, 0);
        wchar_t* buffer = new wchar_t[stringSize];
        MultiByteToWideChar(CP_UTF8 , 0 , txt, -1, buffer, stringSize);

        va_list args;
        va_start(args, txt);
        XDebug::odprintf(buffer,args);

        delete buffer;

        #endif
    }

//private:
#if (CC_TARGET_PLATFORM == CC_PLATFORM_WIN32)
    static void __cdecl odprintf(const wchar_t *format, ...){
    wchar_t    buf[4096], *p = buf;
    va_list args;
    int     n;

            va_start(args, format);
            n = _vsnwprintf(p, sizeof buf - 3, format, args); // buf-3 is room for CR/LF/NUL
            va_end(args);

            p += (n < 0) ? sizeof buf - 3 : n;

            while ( p > buf  &&  isspace(p[-1]) )
                    *--p = '\0';

            *p++ = '\r';
            *p++ = '\n';
            *p   = '\0';

            OutputDebugString(buf);
    }
#endif
};

#endif

Answer 1

You cannot forward varargs between functions like that, for the same reason that you can’t pass args directly to sprintf (you have to use a special vsprintf).

I suggest writing an overload of odprintf that takes a va_list object as a parameter. (And to avoid duplication, you could then implement the original odprintf in terms of the new overload.)