<stdarg.h>

<stdarg.h> provides va_list, va_start(), va_arg(), and va_end() for implementing variadic functions accepting a variable number of arguments. The caller must ensure type safety—there's no runtime checking that passed arguments match what the function expects.

Use an explicit count or sentinel value to bound the argument list.

This example implements a variadic function that finds the minimum of integers.

// compile: gcc -o stdargexample stdargexample.c
// run: ./stdargexample
// description: variadic minimum function
 
#include <stdarg.h>
#include <limits.h>
#include <stdio.h>
 
int vmin(int count, ...) {
    va_list args;
    va_start(args, count);
 
    int result = INT_MAX;
    for (int i = 0; i < count; i++) {
        int v = va_arg(args, int);
        if (v < result) result = v;
    }
 
    va_end(args);
    return result;
}
 
int main() {
    printf("min(3, 7, 1, 9) = %d\n", vmin(4, 3, 7, 1, 9));
    return 0;
}

• va_list: type for argument list pointer
• va_start(ap, last): initialize argument list (last is param before ...)
• va_arg(ap, type): get next argument
• va_end(ap): clean up argument list
• va_copy(dest, src): copy argument list (C99)

    printf("min(42) = %d\n", vmin(1, 42));
    
    return 0;

  } ```