C++ Tutorial Index

C++ Tutorial C++ History C++ Installation C++ First Program C++ cin and cout C++ Data type C++ Variable C++ operator C++ Keywords

C++ Control Statements

C++ If C++ Nested if C++ If-else C++ If-else-if C++ Switch C++ Break C++ Continue C++ Goto C++ For loop C++ While loop C++ Do while loop

C++ Functions

C++ Call by Value C++ Call by Reference C++ Recursion Function C++ Inline function C++ Friend function

C++ Arrays

Single dimension array Two dimension array

C++ Strings

C++ Strings

C++ Inheritance

C++ Inheritance Single level Inheritance Multilevel Inheritance Multiple Inheritance Hierarchical Inheritance Hybrid Inheritance

C++ Polymorphism

C++ Polymorphism C++ Overloading C++ Overriding C++ Virtual Function

C++ Pointers

C++ Pointers C++ this pointer

C++ Exception Handling

C++ Exception Handling

C++ Constructors

C++ Constructors Default Constructor Parameterize Constructor Copy constructor Constructor Overloading Destructor

C++ File Handling

C++ File Handling C++ Writing to file C++ Reading file C++ Close file

Miscellaneous

C Vs C++ C++ Comments C++ Data Abstraction C++ Identifier C++ Memory Management C++ Storage Classes C++ Void Pointer C++ Array To Function C++ Expressions C++ Features C++ Interfaces C++ Encapsulation std::min in C++ External merge sort in C++ Remove duplicates from sorted array in C++ Precision of floating point numbers Using these functions floor(), ceil(), trunc(), round() and setprecision() in C++ C++ References C++ Friend Functions C++ Mutable keyword Unary Operators in C++ Initialize Array of objects with parameterized constructors in C++ Differences between #define & const in C/C++ C++ Program to Implement Shell Sort C++ Program to Implement Merge Sort Storage Classes in C Vector resize() in C++ Passing by Reference Vs. Passing by the pointer in C++ Free vs delete() in C++ goto statement in C and C++ C++ program to read string using cin.getline() C++ String Concatenation Heap Sort in C++ Swap numbers in C++ Input Iterators in C++ Fibonacci Series in C++ C ++ Program: Alphabet Triangle and Number Triangle C++ Program: Matrix Multiplication C++ Program to Print Fibonacci Triangle Stack in C++ Maps in C++ Queue in C++ C++ Bitset C++ Algorithms Priority Queue in C++ C++ Multimap C++ Deque Function Pointer in C++ Sizeof() Operators in C++ C++ array of Pointers free() Vs delete in C Timsort Implementation Using C++ CPP Templates C++ Aggregation C++ Enumeration C++ Math Functions C++ Object Class C++ Queue Initialize Vector in C++ Vector in C++ C++ STL Components Function overloading in C++ C++ Maximum Index Problem C++ find missing in the second array C++ Program to find the product array puzzle C++ Program To Find Largest Subarray With 0 Sum C++ Program To Move All Zeros To The End Of The Array C++ Program to find the element that occurs once C++ Program to find the largest number formed from an array Constructor Vs Destructor C++ Namespaces C++ OOPs Concept C++ Static C++ Structs C++ Try-Catch C++ User Defined Exceptions C++ Virtual Destructor C++ vs C# Malloc() and new in C++ Palindrome Number Program in C++ Snake Code in C++ Splitting a string in C++ Structure Vs Class in C++ Virtual Function Vs Pure Virtual Function C++ Bidirectional Iterators C++ Forward Iterators C++ Iterators C++ Output Iterators C++ Range-based For Loop Converting string into integer in C++ LCM Program in C++ Type conversion in C++ Add two numbers using the function in C++ Advantage and disadvantage friend function C++ Armstrong Number Program in C++ ATM machine program in C++ using functions Binary to Decimal in C++ Bit Manipulation in C++ C++ Constructor C++ Dijkstra Algorithm Using the Priority Queue C++ int into String C++ Signal Handling Decimal to Binary in C++ Decimal to Hexadecimal in C++ Decimal to Octal in C++ Factorial Program in C++ Function in C++ Hexadecimal to Decimal in C++ Octal to Decimal in C++ Reverse a Number in C++ Structure Vs Class in C++ C++ Forward Iterators C++ Output Iterators C++ Prime number program Char Array to String in C++ Constructor Overloading in C++ Default arguments in C++ Different Ways to Compare Strings in C++ Dynamic Binding in C++ Program to convert infix to postfix expression in C++ SET Data Structure in C++ Upcasting and Downcasting in C++ Reverse an Array in C++ Fast Input and Output in C++ Delete Operator in C++ Copy elision in C++ C++ Date and Time C++ Bitwise XOR Operator Array of sets in C++ Binary Operator Overloading in C++ Binary Search in C++ Implementing the sets without C++ STL containers Scope Resolution Operator in C++ Smart pointers in C++ Types of polymorphism in C++ Exception Handling in C++ vs Java Const Keyword in C++ Type Casting in C++ Static keyword in C++ vs Java Inheritance in C++ vs Java How to concatenate two strings in C++ Programs to Print Pyramid Patterns in C++ swap() function in C++ Structure of C++ Program Stringstream in C++ and its applications rand() and srand() in C / C++ C++ Ternary Operator C++ Scope of Variables While Loop Examples in C++ Star pattern in C++ using For Loops For Loop Examples in C++ Do-While Loop Examples in C++ Top 5 IDEs for C++ That You Should Try Once Assertions in C/C++ C++ Convert Int to String Continue in C++ While loop Diamond Pattern in C++ using For Loop How to Reverse a String in C++ using Do-While Loop How to Reverse a String in C++ using For Loop How to Reverse a String in C++ using While Loop Infinite loop in C++ Loops in C++ Returning Multiple Values from a Function using Tuple and Pair in C++ wcscpy(), wcslen(), wcscmp() Functions in C++ Auto keyword in C++ C++ 11 vs C++ 14 vs C++ 17 C++ STL (Standard Template Library) Differences Between C Structures and C++ Structures Divide by Zero Exception in C++ Dynamic Constructor in C++ Dynamic Memory Allocation in C++ Find the Size of Array in C/C++ without using sizeof() function Floating Point Operations and Associativity in C, C++ and Java Hello World Program in C++ How to create a table in C++ How to Setup Environment for C++ Programming on Mac Implementation of a Falling Matrix in C++ Message Passing in C++ Pointer to Object in C++ Templates in C++ vs Generics in Java Ways to Copy a Vector in C++ What does Buffer Flush mean in C++ sort() function in C++ Structure Sorting (By Multiple Rules) in C++ Similarities between C++ and Java std::distance in C++

Function Pointer in C++

Definition:

A function pointer in C++ is the same as a usual pointer which is used to point some variables. Function pointers are used to point functions or say store the address of a function. A function pointer can be used to pass the pointer as a parameter for the other functions and we can call them easily.

Function Address:

We already know that a computer understands only the binary language. In high-level programming languages like C++, a compiler is a program that converts the code into machine understandable and stores it in the executable file. The copy of this executable file is stored in the RAM. When the CPU starts the execution from the main() method, it copies the file from RAM and not the original file.

This process of execution involves occupying some space in the memory. The source code may be a generic one or functional. All these executable source codes occupy space that has an address in RAM. The function pointer has the RAM address of the first instruction of a function.

Syntax: 

int (*foo) (int);                   

OR             

int (*FuncPtr) (int,int);

The above syntax is a function declaration. We know that C++ is a type-safe language and the functions are not simple as defining variables. Therefore, function pointers possess a parameter list and return type. In the above syntax, we have defined the return type and the name of the pointer. The function pointer uses the * operator. There are two integers which are the parameters that are passed with them. In simple words, the function pointer FuncPtr can point to any function which has two integer type parameters and a return value of integer type.

Storing function address:

The function pointer stores the address of the function. We do not need to call the function in the driver code, we just need to mention the function name so that we can easily get the address of the function.

Let us now look at some of the ways through which function pointer stores addresses of functions.

Example 1:

 #include<bits/stdc++.h>
 using namespace std;
 int fool()
 {
     return 5;
 }
 int main()
 {
     cout << fool << '\n';
     return 0;
 } 

Output:

Function Pointer in C++

Explanation:

In the above code, we have declared a function named fool() which returns an integer value 5. To understand this, we need to be clear with the compilers. We have 1 as output in the online GCC compiler while in the other compiler the output may look like - 0xfd23d421.This is nothing but an unreadable memory address that is accessed using a function pointer.

Example 2: Indirect function calling

 #include<bits/stdc++.h>
 using namespace std; 
 int multiply(int x , int y) 
 { 
     return x*y; 
 } 
 int main() 
 { 
                 int (*funcptr)(int,int); 
                 funcptr=multiply;
                 int total=funcptr(4,7); 
                 cout << "Value of multiplication is :" <<total<<endl;
   return 0; 
 }  

Output:

Function Pointer in C++

Explanation:

In the above code, we have used a function pointer to point the function multiply which takes two integer parameters x and y, and returns the multiplication. We have defined a function pointer funcptr that points to the function 'multiply'. The function multiply is passed to the funcptr. This is called an indirect function call. Another variable 'total' stores the value of multiplication which is indirectly passed with both the integer parameters.

The result is then printed on the console.

Note: There can be cases where the function is passed with more or fewer arguments. In such cases, the compiler may return 'too few' or 'too many argument' error.

Example 3: Passing function pointer as a parameter.

  #include<bits/stdc++.h>
 using namespace std; 
 void function1() 
 { 
     cout<<"Function1 is being called!"; 
 } 
 void function2(void (*funcptr)()) 
 { 
     funcptr(); 
 } 
 int main() 
 { 
   function2(function1); 
   return 0; 
 } 

Output:

Function Pointer in C++

Explanation:

In the above code, we have defined two functions named 'function1' and 'function2'. The task is to use function is to pass function pointer as a parameter. To do this, we defined a function pointer 'funcptr' in function2 as a parameter and the pointer is called itself inside the function. When function1 is passed as an argument in function2 then the function pointer 'funcptr' points to function1 and executes the code inside it. By this action, function1 is called as a result and is then displayed on the console.

Note: The main() method calls the function2() in which the address of the function1 is passed. The function2 is calling function1 indirectly.

Points to Remember:

  1. The main task of the function pointer is to allow us to pass a function to a variable and store them for later use.
  • A function pointer is used to point to any function with the same signature.
  • Unlike other pointers, the function pointer does not de-allocate memory.
  • Unlike other pointers, the function pointer points to code, not data.



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