main() -- C Language

Introduce program's main function

A C  program consists of  a set of  functions, one of which  must be called
main(). This function is called  from the runtime startup routine after the
runtime environment has been initialized.

Programs can terminate  in one of two ways.  The  easiest is simply to have
the main()  routine return().  Control returns  to the runtime  startup; it
closes  all open  file streams  and otherwise cleans  up, and  then returns
control to the operating system, passing it the value returned by main() as
exit status.

In some  situations (errors, for  example), it may  be necessary to  stop a
program, and  you may not want  to return to main(). Here,  you can use the
library function exit(); it cleans up the debris left by the broken program
and returns control directly to the operating system.

The system  call _exit()  quickly returns  control to the  operating system
without performing  any cleanup.   This routine  should be used  with care,
because bypassing the cleanup will leave  files open and buffers of data in
memory.

Programs compiled  by COHERENT return  to the program that  called them; if
they return  from main() with  a value or  call exit() with  a value (e.g.,
EXIT_SUCCESS  or EXIT_FAILURE),  main() returns that  value to  the program
that invoked  it (e.g.,  the shell).   Programs that invoke  other programs
through  the function  system() check  the returned value  to see  if these
secondary  programs  terminated  successfully.   If  you exit  from  main()
without explicitly  returning a value (e.g., by  just letting main() simply
conclude, or  by invoking  exit() without a  return status, or  by invoking
return  without  a  return value),  main()  returns  whatever random  value
happens to have been in the register EAX.

See Also

_exit(),
argc,
argv,
C language,
envp,
exit(),
EXIT_FAILURE,
EXIT_SUCCESS
ANSI Standard, §5.1.2.2.1
POSIX Standard, §3.1.2.2

© 2012 by Stephen A. Ness