Thread: Help with Variadic Macro Function

OK, so what I'm doing right now is creating a function that callocs (I prefer this to malloc) and returns a string, and it will work similar to printf, I'm calling the function alloCpy(), the idea is this:
I have several values that I need in a malloced string, so I call

Code:

myAllocedString = alloCpy("Value 1 is %s, value 2 is %s, and value 3 is %d", str1, str2, num);

To do this I'm using the Variadic Macro, the reason I'm not just using a Variadic Function such as this:

Code:

char* alloCpy(char *format, ...) {}

is because I need to append NULL to the end for the sake of looping through arguments, and I'm understanding it thusfar, but I have a few issues, first of all, I tried defining the Macro in a header file, but when I try to call it I get the error "Undefined reference to alloCpy". Also, to loop through arguments to get string lengths I'm using va_arg(args, char*) which requires all the arguments to be of type char*. Here is my code:
myheader.h:

Code:

#define alloCpy(format, ...) _alloCpy(format, ##__VA_ARGS__, NULL);
char* _alloCpy(char *format, ...);

mycfile.c:

Code:

char* _alloCpy(char *format, ...) {
    va_list args;
    va_start(args, format);
    int args_len = 0;


    char *arg;
    for(arg = va_arg(args, char*); arg != NULL; arg = va_arg(args, char*))
        args_len += strlen(arg);


    // Allocated memory will have extra padding because of formatting chars (%s, %d, etc.)
    char *dest = calloc(strlen(format) + args_len + 1, sizeof(char));
    vsprintf(dest, format, args);


    return dest;
}

So, how can I do this to, first of all, make my macro function accessible from other files importing myheader.h, and second, how can I make it accept any type of argument like printf, so that my example above would work?

@Salem
That's exactly what I needed! Thanks, I don't know why I didn't think of that, I was totally over complicating it.