Pass a variable number of arguments to an aliased function.

Question

Take a function like printf that accepts a variable number of arguments what I would like to do is pass these variable number of functions to a sub function without changing their order. An example of this would be aliasing the printf function to a function called console ...

#include <stdio.h>

void console(const char *_sFormat, ...);

int main () {
    console("Hello World!");
    return 0;
}

void console(const char *_sFormat, ...) {
    printf("[APP] %s\n", _sFormat);
}

If I did for example console("Hello %s", sName), I would want the name to be passed to the printf function also, but it has to be able to continue to accept a varable number of arguments like the printf already does.

Answer 1

There'll be another problem (noted by gf) -- you should probably concatenate the string in printf and the _sFormat parameter -- I doubt that printf is recursive -- hence the format statements in the first parameter wont be read!

Hence maybe such a solution would be nicer:

#include <stdarg.h>

void console(const char *_sFormat, ...)
{
  char buffer[256];

  va_list args;
  va_start (args, _sFormat);
  vsprintf (buffer,_sFormat, args);
  va_end (args);

  printf("[APP] %s\n", buffer);
}

Types/functions used:

• va_list
• va_start
• va_end

Answer 2

Here's what you want:

#include <stdio.h>
#include <stdarg.h>

void console(const char *_sFormat, ...);

int main () {
    console("Hello World!");
    return 0;
}

void console(const char *_sFormat, ...) {
    va_list ap;
    va_start(ap, _sFormat);
    printf("[APP] ");
    vprintf(_sFormat, ap);
    printf("\n");
    va_end(ap);
}