Question

How I make the following code work? I want to print “non defined” instead of -1.#IND00

int myprint(const char* format, ...)
{
    va_list args;
    va_start (args, format);
    int ret;
    if(_isnan(static_cast<float>(*args)))
        ret = printf ("non defined");
    else
        ret = vprintf (format, args);
    fflush(stdout);
    va_end (args); 
    return ret; 
}

int main()
{
    myprint("%f", sqrt(-1.0));
    return 0;
}

Answer 1

You can’t use args like that, you have to use va_arg to get an actual argument.

if(_isnan(va_arg(args,double)))

would do the trick, but that won’t help you much. You can’t infer the type from the arguments. The type you indicate to va_arg must be the actual type of the object passed in.

And with that, your vprintf call won’t work either, you need to “re-start” the va_list since va_arg has “consumed” one argument already.