How to tell a va_list object is empty?

For example, I have

Code:

void INFO(const char* fmt, ...){
  char buf[1024]
  va_list ap;
  vsnprintf(buf, 1024, fmt, ap);
  va_end(ap);
  return;
}

I want to pass in 2 types: INFO("str") and INFO("str, %d", int). For the 2 types, shall I tell if ap is empty?

There is no way to tell by looking at the va_list. When you see the "%d" you assume there is an argument.

Originally Posted by brewbuck

There is no way to tell by looking at the va_list. When you see the "%d" you assume there is an argument.

If I call INFO("str"), will there be an error?

Yes, because you don't initialize the va_list with va_start. Other than that, no.

Other than that, no.

Well, that, and other than that missing semicolon.

Code:

void INFO(const char* fmt, ...){
  char buf[1024];
  va_list ap;
  va_start(ap, fmt);
  vsnprintf(buf, 1024, fmt, ap);
  va_end(ap);
  return;
}

That return is unnecessary as well. And consider using sizeof() rather than hard-coding 1024 into that vsnprintf() call.