exit() vs _Exit() in C and C++

In C, exit() terminates the calling process without executing the rest code which is after the exit() function.

Example:-

// C program to illustrate exit() function. 
#include <stdio.h> 
#include <stdlib.h> 
int main(void) 
{ 
    printf("START"); 
  
    exit(0); // The program is terminated here 
  
    // This line is not printed 
    printf("End of program"); 
} 

Output:

START

Now the question is that if we have exit() function then why C11 standard introduced _Exit()? Actually exit() function performs some cleaning before termination of the program like connection termination, buffer flushes etc. The _Exit() function in C/C++ gives normal termination of a program without performing any cleanup tasks. For example it does not execute functions registered with atexit.

Syntax:

// Here the exit_code represent the exit status 
// of the program which can be 0 or non-zero.
// The _Exit() function returns nothing.
void _Exit(int exit_code);

// C++ program to demonstrate use of _Exit() 
#include <stdio.h> 
#include <stdlib.h> 
int main(void) 
{ 
    int exit_code = 10; 
    printf("Termination using _Exit"); 
    _Exit(exit_code); 
  
} 

Output:

Showing difference through programs:

// A C++ program to show difference 
// between exit() and _Exit() 
#include<bits/stdc++.h> 
using namespace std; 
  
void fun(void) 
{ 
   cout << "Exiting"; 
} 
  
int main() 
{ 
   atexit(fun); 
   exit(10); 
} 

Output

Exiting

If we replace exit with _Exit(), then nothing is printed.

// A C++ program to show difference 
// between exit() and _Exit() 
#include<bits/stdc++.h> 
using namespace std; 
  
void fun(void) 
{ 
   cout << "Exiting"; 
} 
  
int main() 
{ 
   atexit(fun); 
   _Exit(10); 
} 

Output

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.

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