Go4Expert - OutputDebugString with variable number of arguments

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OutputDebugString with variable number of arguments

Most often a question comes in my mind that why OutputDebugString does not take variable no of arguments like the TRACE or printf function. I dont know the reason why but I have a solution to the problem.

This article is for those OutputDebugString fan's who are annoyed to use the CString and format the string with the variables like

Code: CPP

CString OutMsg;
OutMsg.Format("FUNCTION NAME >> VARIABLE NAME = %d",VAR_NAME);
OutputDebugString(OutMsg);

Here is the substituted function

Code: CPP

void _OutputDebugString(LPCTSTR lpOutputString, ... )
{
    
    va_list argptr;    
    
    va_start( argptr, lpOutputString );            
    
    TCHAR OutMsg[MAX_LENGTH];
    TCHAR format[MAX_LENGTH];
    
    for(int i=0,j=0;lpOutputString[i] != '\0';i++) 
    {
        format[j++] = lpOutputString[i];
        // If escape character
        if(lpOutputString[i] == '\\')
        {
            i++;
            continue;
        }
        // if not a substitutal character
        if(lpOutputString[i] != '%')
            continue;
        
        format[j++] = lpOutputString[++i];
        format[j] = '\0';
        switch(lpOutputString[i])
        {
            // string
        case 's':
            {
                char* s = va_arg( argptr, char * );
                sprintf(OutMsg,format,s);
                strcpy(format,OutMsg);
                j = strlen(format);
                strcat(format," ");
                break;
            }
            // character
        case 'c':
            {
                char c = (char) va_arg( argptr, int );
                sprintf(OutMsg,format,c);
                strcpy(format,OutMsg);
                j = strlen(format);
                strcat(format," ");
                break;
            }
            // integer
        case 'd':
            {
                int d = va_arg( argptr, int );
                sprintf(OutMsg,format,d);
                strcpy(format,OutMsg);
                j = strlen(format);
                strcat(format," ");
                break;
            }
        }
    }           
    OutputDebugString(OutMsg);
    va_end( argptr );
}

Download the cpp file and see how it works.

I have taken care of escape character \, string %s, integers %d and characters %c but you can add the floating point numbers and many more.