Variadic function (variable number of arguments)

This program demonstrates the use of variadic functions in C by implementing a function, myMaxFunc, that can accept a variable number of arguments and return the maximum value among them.

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

int myMaxFunc(int num_args, ...);

int main(){

    int myMaxVar = myMaxFunc(4, 14, 89, 12, 56);

    printf("Max number is: %d\n", myMaxVar);

    return 0;
}

int myMaxFunc(int num_args, ...){

    va_list args;
    
    va_start(args, num_args);

    int max_num = 0;

    for (int i=0; i<num_args; i++){
        int x = va_arg(args, int); 
        if (i==0){ 
            max_num = x; 
        } else if (x > max_num) {
            max_num = x;
        }
    }

    va_end(args);

    return max_num;
}

Code Explanation

1. Header Files

• #include <stdio.h>: Provides the printf() function for output.
• #include <stdarg.h>: Provides macros for handling variadic arguments (va_list, va_start, va_arg, and va_end).

2. Main Function

• calls the myMaxFunc function with four integer arguments: 14, 89, 12, 56.
• stores the maximum value returned by myMaxFunc in the variable myMaxVar.
• prints the maximum value.

3. Variadic Function

• definition: int myMaxFunc(int num_args, ...):
  • the first parameter, num_args, specifies the number of arguments passed to the function.
  • the ... syntax indicates that the function can accept a variable number of additional arguments.
• implementation:
  • A va_list variable is declared to access the variadic arguments.
  • va_start(args, num_args) initializes the va_list to access the arguments.
  • A loop iterates through the arguments using va_arg(args, int) to fetch each argument as an integer.
  • Compares each argument to determine the maximum value.
  • va_end(args) is called to clean up the va_list after processing.

4. Output

Max number is: 89

Conclusion

This program illustrates the power of variadic functions in C, which allow developers to create flexible functions that can handle an arbitrary number of arguments. Variadic functions are widely used in standard libraries, such as printf(), for implementing variable-length parameter lists. Understanding and using variadic functions is essential in scenarios where the number of inputs may vary at runtime, making the code more general and adaptable. However, developers must carefully manage argument types and memory to avoid errors or undefined behavior.