C++ program termination

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In C++, you can exit a program in these ways:

  • Call the exit function.
  • Call the abort function.
  • Execute a return statement from main.

exit function

The exit function, declared in <stdlib.h>, terminates a C++ program. The value supplied as an argument to exit is returned to the operating system as the program's return code or exit code. By convention, a return code of zero means that the program completed successfully. You can use the constants EXIT_FAILURE and EXIT_SUCCESS, also defined in <stdlib.h>, to indicate success or failure of your program.

Issuing a return statement from the main function is equivalent to calling the exit function with the return value as its argument.

abort function

The abort function, also declared in the standard include file <stdlib.h>, terminates a C++ program. The difference between exit and abort is that exit allows the C++ run-time termination processing to take place (global object destructors get called), but abort terminates the program immediately. The abort function bypasses the normal destruction process for initialized global static objects. It also bypasses any special processing that was specified using the atexit function.

atexit function

Use the atexit function to specify actions that execute before the program terminates. No global static objects initialized before the call to atexit are destroyed before execution of the exit-processing function.

return statement in main

Issuing a return statement from main is functionally equivalent to calling the exit function. Consider the following example:

            // return_statement.cpp #include <stdlib.h> int main() {     exit( 3 );     return 3; }

The exit and return statements in the preceding example are functionally identical. Normally, C++ requires that functions that have return types other than void return a value. The main function is an exception; it can end without a return statement. In that case, it returns an implementation-specific value to the invoking process. The return statement allows you to specify a return value from main.

Destruction of static objects

When you call exit or execute a return statement from main, static objects are destroyed in the reverse order of their initialization (after the call to atexit if one exists). The following example shows how such initialization and cleanup works.

Example

In the following example, the static objects sd1 and sd2 are created and initialized before entry to main. After this program terminates using the return statement, first sd2 is destroyed and then sd1. The destructor for the ShowData class closes the files associated with these static objects.

            // using_exit_or_return1.cpp #include <stdio.h> class ShowData { public:    // Constructor opens a file.    ShowData( const char *szDev ) {    errno_t err;       err = fopen_s(&OutputDev, szDev, "w" );    }     // Destructor closes the file.    ~ShowData() { fclose( OutputDev ); }     // Disp function shows a string on the output device.    void Disp( char *szData ) {       fputs( szData, OutputDev );    } private:    FILE *OutputDev; };  //  Define a static object of type ShowData. The output device //   selected is "CON" -- the standard output device. ShowData sd1 = "CON";  //  Define another static object of type ShowData. The output //   is directed to a file called "HELLO.DAT" ShowData sd2 = "hello.dat";  int main() {    sd1.Disp( "hello to default device\n" );    sd2.Disp( "hello to file hello.dat\n" ); }

Another way to write this code is to declare the ShowData objects with block scope, allowing them to be destroyed when they go out of scope:

            int main() {    ShowData sd1( "CON" ), sd2( "hello.dat" );     sd1.Disp( "hello to default device\n" );    sd2.Disp( "hello to file hello.dat\n" ); }

See also

main function and command-line arguments