Question

#define MAX_LENGTH_STRING 4096
void BugCode()
{   
    char szLine[MAX_LENGTH_STRING] = {0};
    char szSelection[MAX_LENGTH_STRING] = {0};
    va_list my_args;

    szSelection[0]= 0xe7  ;  
    szSelection[1]= 0xac  ;  
    szSelection[2]= 0xac  ;  
    szSelection[3]= 0xe4  ;  
    szSelection[4]= 0xb8  ;  
    szSelection[5]= 0x80  ;  
    szSelection[6]= 0xe5  ;  
    szSelection[7]= 0x8d  ;  
    szSelection[8]= 0x95  ;  
    szSelection[9]= 0x00  ;  


    va_start(my_args, szSelection);

#ifdef WIN32
    _vsnprintf(szLine, MAX_LENGTH_STRING-1, szSelection, my_args);
#else
    vsnprintf(szLine, MAX_LENGTH_STRING - 1, szSelection, my_args);
#endif
}

The BugCode() would crash at _vsnprintf()
But if I copy&paste these code to a simple project, it works well…

Answer 1

You’re not using va_start correctly. va_start (and va_list) can only be used for variadic function arguments. Using them for any other purpose is undefined behaviour.