What is the difference between exit and return

Question

What is difference between return and exit statement in C programming when called from anywhere in a C program

User · Answer

In C  there s not much difference when used in the startup function of the program  which can be main    wmain     tmain   or the default name used by your compiler    If you return in main    control goes back to the  start   function in the C library which originally started your program  which then calls exit   anyways  So it really doesn t matter which one you use

User · Answer

I wrote two programs   int main   return 0     and   include  lt stdlib h gt  int main   exit 0     After executing gcc -S -O1  Here what I found watching at assembly  only important parts    main      movl     0   eax       setting return value        ret                    return from main      and  main      subq     8   rsp       reserving some space        movl     0   edi       setting return value        call    exit           calling exit function                               magic and machine specific wizardry after this call      So my conclusion is  use return when you can  and exit   when you need

User · Answer

return returns from the current function  it s a language keyword like for or break  exit   terminates the whole program  wherever you call it from    After flushing stdio buffers and so on    The only case when both do  nearly  the same thing is in the main   function  as a return from main performs an exit    In most C implementations  main is a real function called by some startup code that does something like int ret   main argc  argv   exit ret     The C standard guarantees that something equivalent to this happens if main returns  however the implementation handles it  Example with return   include  lt stdio h gt   void f        printf  quot Executing f n quot        return     int main        f        printf  quot Back from f n quot       If you execute this program it prints   Executing f Back from f   Another example for exit     include  lt stdio h gt   include  lt stdlib h gt   void f        printf  quot Executing f n quot        exit 0      int main        f        printf  quot Back from f n quot       If you execute this program it prints   Executing f   You never get  quot Back from f quot    Also notice the  include  lt stdlib h gt  necessary to call the library function exit    Also notice that the parameter of exit   is an integer  it s the return status of the process that the launcher process can get  the conventional usage is 0 for success or any other value for an error   The parameter of the return statement is whatever the return type of the function is  If the function returns void  you can omit the return at the end of the function  Last point  exit   come in two flavors  exit   and exit     The difference between the forms is that exit    and return from main  calls functions registered using atexit   or on exit   before really terminating the process while  exit    from  include  lt unistd h gt   or its synonymous  Exit from  include  lt stdlib h gt   terminates the process immediately  Now there are also issues that are specific to C    C   performs much more work than C when it is exiting from functions  return-ing   Specifically it calls destructors of local objects going out of scope  In most cases programmers won t care much of the state of a program after the processus stopped  hence it wouldn t make much difference  allocated memory will be freed  file ressource closed and so on  But it may matter if your destructor performs IOs  For instance automatic C   OStream locally created won t be flushed on a call to exit and you may lose some unflushed data  on the other hand static OStream will be flushed   This won t happen if you are using the good old C FILE  streams  These will be flushed on exit    Actually  the rule is the same that for registered exit functions  FILE  will be flushed on all normal terminations  which includes exit    but not calls to  exit   or abort    You should also keep in mind that C   provide a third way to get out of a function  throwing an exception  This way of going out of a function will call destructor  If it is not catched anywhere in the chain of callers  the exception can go up to the main   function and terminate the process  Destructors of static C   objects  globals  will be called if you call either return from main   or exit   anywhere in your program  They wont be called if the program is terminated using  exit   or abort    abort   is mostly useful in debug mode with the purpose to immediately stop the program and get a stack trace  for post mortem analysis   It is usually hidden behind the assert   macro only active in debug mode  When is exit   useful   exit   means you want to immediately stops the current process  It can be of some use for error management when we encounter some kind of irrecoverable issue that won t allow for your code to do anything useful anymore  It is often handy when the control flow is complicated and error codes has to be propagated all way up  But be aware that this is bad coding practice  Silently ending the process is in most case the worse behavior and actual error management should be preferred  or in C   using exceptions   Direct calls to exit   are especially bad if done in libraries as it will doom the library user and it should be a library user s choice to implement some kind of error recovery or not  If you want an example of why calling exit   from a library is bad  it leads for instance people to ask this question  There is an undisputed legitimate use of exit   as the way to end a child process started by fork   on Operating Systems supporting it  Going back to the code before fork   is usually a bad idea  This is the rationale explaining why functions of the exec   family will never return to the caller

User · Answer

the return statement exits from the current function and exit   exits from the program  they are the same when used in main   function   also return is a statement while exit   is a function which requires stdlb h header file

[c] What is the difference between exit and return?

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