C Tutorial

C Tutorial C Language Environment Setup Execution flow of C program C printf and Scanf C Data type C Token Variable in C Operators in C Comments in C Escape Sequence in C C – Storage Classes C Decision control statement Loop Statement in C Break, continue and goto statement in C Type Casting in C Function in C Recursion in C String in C C Array Pointer in C Dynamic memory allocation C –Structure Nested Structure in C Union in C File Handling in C C pre-processor Static Function In C Sizeof In C Selection Sort In C Scope Of Variables In C Runtime Vs Compile Time In C Random Access Lseek In C Queue Implementation In C Pseudo Code In C Prototype In C Pointer To Pointer In C Pointer Arithmetic In C Passing Array To Function In C Null Character In C Merge Sort In C Macros In C Library Functions In C Memory Leak In C Int In C Goto And Labels In C Fibonacci Series In C Fflush In C Derived Data Types In C Data Types In C Const Vs Volatile In C Character Set In C Character Class Tests In C Calloc In C C Pointers Arrays In C Include In C Clrscr In C C Vs Java String Literals In C Types Of Pointers In C Variables In C Volatile In C Why C Is A Middle Level Language Infix To Postfix Program In C Ceil function in C LCM of two numbers in C Quick sort in C Static in C function pointer as argument in C Top Array Keywords in C Add two numbers using the function in C Armstrong program in C using function Array, Declaring Arrays and Array Initialization Limitations of Inline Function in C Merge and Merge sort with example in C Do-While Loop in C For Loop in C While-Loop in C Difference between while and do-while loop in C Array Of Structures in C Data Structures And Algorithms in C Types Of Structures In C How to Avoid Structure Padding in C Use of Structure in C Do WHILE LOOP in C Programming Examples For Loop in C Programming Examples Entry Control Loop in C Exit control loop in C Infinite loop in C Nested loop in C pow() function in C String Handling functions in C Prime Number code in C Factorial Program in C using For Loop Factorial Program in C Using While Loop Fibonacci Series in C Using For Loop Fibonacci series in C using while loop Prime Number Program in C using for Loop While Loop in C programming examples Built-in functions in C Assert() Function C vs Java Strings Call Back Function in Embedded C Else If Ladder fgets() function Ftell() Function getc() function getch() function gets() function Heap Sort Nested if-else statement Pi() Function Positioning of file Write() function abs() function in C Attributes in C C program to find factorial of a number using Recursion Ferror() in c fopen() function in C Fibonacci series program in C using Recursion Formatted Input and output function in C Snake Game in C User Defined Functions in C Beep() function in C Cbrt() function in C Hook() function in C Isalnum() function in C C Program to find the Roots of a Quadratic Equation C Switch Statements Difference between rand() and srand() function in C Difference between while and for loop in C Doubly Linked list in C Example of Iteration in C How to use atoi() function in C How to use floor() function in C How to use sine() function in C How to use Typedef Struct in C Integer Promotions in C C Program Swap Numbers in cyclic order Using Call by Reference C Program to Find Largest Number Using Dynamic Memory Allocation C Program to Find the Largest Number using Ternary Operator C/C++ Program to Find the Size of int, float, double and char Find the Largest Three Distinct Elements in an Array using C/C++ Loop Questions in C Modulus on Negative Numbers in C Multiplication table program in C using For loop Nested Loops in C Programming Examples C Program for Mean and Median of an Unsorted Array Results of Comparison Operations in C and C++ Reverse a Stack using Recursion in C Simple hash() function in C strcat() Function in C Sum of N numbers in C using For loop Use of free() function in C Write a program that produces different results in C and C++ C Function Argument and Return Values Keywords in C Bank management system in C Calendar application in C Floor() Function in C Free() Function in C How to delete a file in C How to move a text in C Remove an element from an array in C Unformatted input() and output() function in C What are linker and loader in C fork() in C GCD program in C Branching Statements in C Comma Operator in C Control statement in C Double Specifier in C How to create a binary file in C Long int in C Palindrome Number in C Pure Virtual Function in C Run Time Polymorphism in C Types of Array in C Types of Function in C What is a buffer in C What is required in each C Program Associativity of Operators in C Bit Stuffing Program in C Actual and Formal Parameters Addition of two Numbers in C Advantages of function in C Arithmetic Progression Program in C Binomial Coefficient Program in C Difference between Array and List in C Diffie-Hellman Algorithm in C How to convert a number to words in C How to convert a string to hexadecimal in C Difference between If and Switch Statement in C

function pointer as argument in C

Pointers are considered difficult to understand for beginners but pointers can be made to work if you fiddle with them long enough. So, let’s understand this step by step.

What are Pointers?

A pointer is a variable and this variable contains the address of another variable, i.e., it’s a variable which has the address of another variable as its value. The utilization of pointers is to access the memory and also, to govern the address (manipulation of address).

For eg, If a  is a variable of type int having value \0  stored at address 3000 and address of a is assigned to some other variable b, then b  is a pointer variable pointing to memory address stored in it. In simple words, b is a pointer variable containing the address of a (i.e., 3000).

Passing Addresses to Functions

An argument is the value that is passed to the function by the user who calls the function. There are two ways in which arguments are generally passed to functions and they are passed in one of the following ways:

by sending;

a) the values of the arguments
b) the addresses of the arguments

In the first method (a), the value of every actual argument within the calling function is copied into the resemblant formal argument of the function which is called.

In this article, we are more concerned about the second way, i.e., Sending the addresses of the arguments.

Function Pointer as argument in C

The method(b) suggests that Pointers can be passed to a function as arguments. When an address is passed to a function, then the parameters which receive the address should be pointers. In simple words, we are able to relay the reference of a function as a parameter by employing a function pointer. This method of passing parameters is called the Call by Reference method.

Here, an individual must recognize that if any modification is introduced by the function using pointers, then it’ll also mirror the modifications at the address of the passed variable. What this suggests is that any changes made are recognized in both the functions and therefore the calling routine.

Function pointer as argument in C

In above figure,

func1() is a function in which arguments passed are addresses of a and b and no value is returned by this function therefore void data type is mentioned before the function.

In function definition, we have formal arguments as pointer variables that are local to the block in which they are defined.

In C, a function pointer is often created or declared as follows:

(type) (*pointerName) (parameter);

Here,  type       = variable type which is returned by the function

*pointerName  = function pointer

parameter       = list of arguments passed(to the function)

In the call by reference method, what actually happens is that the addresses of actual arguments within the calling function are copied into formal arguments of the called function.

What can we mean by this technical jargon?

This statement simply states that using the formal arguments within the called function is that we are able to make changes within the actual arguments of the calling function.

Let’s understand this using a C program,

main()
{
int x = 5;
int y = 10;


void swap (int*p, int *q);
swap (&x, &y);
printf(“\nx = %d”, x);
printf(“\ny = %d”, y);
           }




void swap (int*p, int*q)
{
int s;
s = *p;
          *p = *q;
          *q = s;
}

Output

x = 10;

y = 5;

In the above code,

→ The address of two numbers is passed to a function swap() whose arguments are pointer type variables.

→ When values are passed, the values assigned to pointer (*p and *q) are changed. It means new values will be assigned to them.

→ This change in addresses is passed to the main() function where they are printed.

*Note: A function pointer can even point to a different function, or in other words that it can hold the address of another function.

            Eg:

            int sum (int x, int y); // function declaration

            int (*x) (int, int); //  declaration of a pointer to a function

           x = sum; // assigning address of sum() to ‘x’ pointer



ADVERTISEMENT
ADVERTISEMENT