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12.6 Exiting Portably

A C or C++ program can exit with status N by returning N from the main function. Portable programs are supposed to exit either with status 0 or EXIT_SUCCESS to succeed, or with status EXIT_FAILURE to fail, but in practice it is portable to fail by exiting with status 1, and test programs that assume Posix can fail by exiting with status values from 1 through 255. Programs on SunOS 2.0 (1985) through 3.5.2 (1988) incorrectly exited with zero status when main returned nonzero, but ancient systems like these are no longer of practical concern.

A program can also exit with status N by passing N to the exit function, and a program can fail by calling the abort function. If a program is specialized to just some platforms, it can fail by calling functions specific to those platforms, e.g., _exit (Posix) and _Exit (C99). However, like other functions, an exit function should be declared, typically by including a header. For example, if a C program calls exit, it should include stdlib.h either directly or via the default includes (see Default Includes).

A program can fail due to undefined behavior such as dereferencing a null pointer, but this is not recommended as undefined behavior allows an implementation to do whatever it pleases and this includes exiting successfully.

  Published under the terms of the GNU General Public License Design by Interspire