Variable arguments

[frank]

I am declaring a local buffer of a fixed size in my variable argument
routine. How do I figure out the correct size of the variable argument list
so that I can dynamically allocate the memory?

void disp_message(ch ar *szCaption, char *szFormat, ...)
{
va_list ap;
char szBuffer[4096] = { 0 };

va_start(ap, szFormat);
vsprintf(szBuff er, szFormat, ap);
va_end(ap);

// Display the message.
MessageBox(NULL , szBuffer, szCaption, MB_OK | MB_ICONWARNING) ;
}

[Eric Sosman]

Re: Variable arguments

frank wrote:[color=blue]
> I am declaring a local buffer of a fixed size in my variable argument
> routine. How do I figure out the correct size of the variable argument list
> so that I can dynamically allocate the memory?[/color]

Try vsnprintf(). It's a C99 addition, but is available
in some pre-C99 implementations , too. Use some caution with
pre-C99 versions, since their semantics may not be exactly
those that were eventually codified in the C99 Standard.
[color=blue]
> void disp_message(ch ar *szCaption, char *szFormat, ...)
> {
> va_list ap;
> char szBuffer[4096] = { 0 };[/color]

The initialization is pointless (because you're about
to overwrite the buffer anyhow) and potentially wasteful
(because you're about to overwrite all those carefully-
inserted zeroes).
[color=blue]
> va_start(ap, szFormat);
> vsprintf(szBuff er, szFormat, ap);
> va_end(ap);
>
> // Display the message.
> MessageBox(NULL , szBuffer, szCaption, MB_OK | MB_ICONWARNING) ;
> }[/color]

--
Eric.Sosman@sun .com