Variadic Functions In C

Variadic Functions In C

Variadic functions in C are like flexible functions because they can accept different numbers of arguments. They always have at least one fixed argument, and then you can pass any number of additional arguments. To indicate this flexibility, variadic functions have an ellipsis (…) as their last parameter.

Syntax

int function_name(data_type variable_name, ...);

Values of the passed arguments can be accessed through the header file named as:

#include <stdarg.h>

<stdarg.h> includes the following methods:

Methods	Description
va_start(va_list ap, argN)	This method will grant access to variadic function arguments. Whereas, *va_list* will be the pointer to the last fixed argument in the variadic function* and, it is the last fixed argument in the variadic function. Hence, From the above variadic function (function_name (data_type variable_name, …);) provided, We can conclude that variable_name is the last fixed argument making it the argN. *va_list ap* will be a pointer to argN (variable_name)
va_arg(va_list ap, type)	In this method, it will give access to the next variadic function argument. Also, *va_list ap* is the same as above i.e. a pointer to argN*type*, and it refers to the data type  the *va_list ap* should expect (double, float, int, etc.)
va_copy(va_list dest, va_list src)	This method can create a copy of the variadic function arguments.
va_end(va_list ap)	This indicates the passing of the variadic function arguments.

Note

va_list holds the information needed by va_start, va_arg, va_end, and va_copy

Program 1: C program to illustrate the working of variadic function

// C program for the above approach
 
#include <stdarg.h>
#include <stdio.h>
 
// Variadic function to add numbers
int AddNumbers(int n, ...)
{
    int Sum = 0;
 
    // Declaring pointer to the
    // argument list
    va_list ptr;
 
    // Initializing argument to the
    // list pointer
    va_start(ptr, n);
 
    for (int i = 0; i < n; i++)
   // Accessing current variable
        // and pointing to next one
        Sum += va_arg(ptr, int);
 
    // Ending argument list traversal
    va_end(ptr);
 
    return Sum;
}
 
// Driver Code
int main()
{
    printf("\n\n Variadic functions: \n");
 
    // Variable number of arguments
    printf("\n 1 + 2 = %d ",
           AddNumbers(2, 1, 2));
 
    printf("\n 3 + 4 + 5 = %d ",
           AddNumbers(3, 3, 4, 5));
 
    printf("\n 6 + 7 + 8 + 9 = %d ",
           AddNumbers(4, 6, 7, 8, 9));
 
    printf("\n");
 
    return 0;
}

Output

Variadic functions: 

 1 + 2 = 3 
 3 + 4 + 5 = 12 
 6 + 7 + 8 + 9 = 30

Program 2: C program consisting of the variadic function LargestNumber()

// C program for the above approach
#include <stdarg.h>
#include <stdio.h>
 
// Variadic function to find the largest number
int LargestNumber(int n, ...)
{
      // Declaring pointer to the
    // argument list
    va_list ptr;
 
    // Initializing argument to the
    // list pointer
    va_start(ptr, n);
   
    int max = va_arg(ptr, int);
 
    for (int i = 0; i < n-1; i++) {
 
        // Accessing current variable
        // and pointing to next
        int temp = va_arg(ptr, int);
        max = temp > max ? temp : max;
    }
 
    // End of argument list traversal
    va_end(ptr);
 
    return max;
}
 
// Driver Code
int main()
{
    printf("\n\n Variadic functions: \n");
 
    // Variable number of arguments
    printf("\n %d ",
           LargestNumber(2, 1, 2));
 
    printf("\n %d ",
           LargestNumber(3, 3, 4, 5));
 
    printf("\n %d ",
           LargestNumber(4, 6, 7, 8, 9));
 
    printf("\n");
 
    return 0;
}

Output

Variadic functions: 

 2 
 5 
 9

FAQ- Variadic Functions In C