Variadic functions

Variadic functions are functions (e.g. printf) which take a variable number of arguments.

The declaration of a variadic function uses an ellipsis as the last parameter, e.g. int printf(const char* format, ...);. See Variadic arguments for additional detail on the syntax and automatic argument conversions.

Accessing the variadic arguments from the function body uses the following library facilities:

Defined in header <stdarg.h>
Macros
va_start	enables access to variadic function arguments (function macro)
va_arg	accesses the next variadic function argument (function macro)
va_copy (C99)	makes a copy of the variadic function arguments (function macro)
va_end	ends traversal of the variadic function arguments (function macro)
Type
va_list	holds the information needed by va_start, va_arg, va_end, and va_copy (typedef)

Example

Print values of different types.

Run this code

#include <stdio.h>
#include <stdarg.h>
 
void simple_printf(const char* fmt,...)
{
    va_list args;
    va_start(args, fmt);
 
    while (*fmt != '\0') {
        if (*fmt == 'd') {
            int i = va_arg(args, int);
            printf("%d\n", i);
        } else if (*fmt == 'c') {
            // note automatic conversion to integral type
            int c = va_arg(args, int);
            printf("%c\n", c);
        } else if (*fmt == 'f') {
            double d = va_arg(args, double);
            printf("%f\n", d);
        }
        ++fmt;
    }
 
    va_end(args);
}
 
int main(void)
{
    simple_printf("dcff", 3, 'a', 1.999, 42.5); 
}

Output:

3
a
1.999000
42.50000

See also

C++ documentation for Variadic functions