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Full Discussion: Function main returning int?
Top Forums Programming Function main returning int? Post 302727113 by jim mcnamara on Monday 5th of November 2012 08:07:54 PM
Old 11-05-2012
Read the main page on waitpid or wait to get more detail.

The return value of a process to the calling is process is the least significant eight bits of the number returned by main(). Which can be seen as signed or unsigned by the parent. So, the valid results from calling wait on a child returns values from 0 to 255 (looked at as unsigned).

By convention 0 means success, as defined in C by EXIT_SUCCESS.

Since main() is an int function you can return any valid int, but is not very useful to return numbers larger than the range I just defined.

Code:
// retval.c
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char **argv)
{
     int retval=atoi(argv[1]);
     printf("I am returning %d\n", retval);
     return retval;
}

Compile retval then run it with this script
Code:
#!/bin/ksh
cnt=1
while [ $cnt -le 100000000 ]
do
       retval $cnt
       cnt=$((  $cnt * 10 ))
done

And see what happens...
 

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PTHREAD_EXIT(3) 					     Linux Programmer's Manual						   PTHREAD_EXIT(3)

NAME
pthread_exit - terminate calling thread SYNOPSIS
#include <pthread.h> void pthread_exit(void *retval); Compile and link with -pthread. DESCRIPTION
The pthread_exit() function terminates the calling thread and returns a value via retval that (if the thread is joinable) is available to another thread in the same process that calls pthread_join(3). Any clean-up handlers established by pthread_cleanup_push(3) that have not yet been popped, are popped (in the reverse of the order in which they were pushed) and executed. If the thread has any thread-specific data, then, after the clean-up handlers have been executed, the corresponding destructor functions are called, in an unspecified order. When a thread terminates, process-shared resources (e.g., mutexes, condition variables, semaphores, and file descriptors) are not released, and functions registered using atexit(3) are not called. After the last thread in a process terminates, the process terminates as by calling exit(3) with an exit status of zero; thus, process- shared resources are released and functions registered using atexit(3) are called. RETURN VALUE
This function does not return to the caller. ERRORS
This function always succeeds. CONFORMING TO
POSIX.1-2001. NOTES
Performing a return from the start function of any thread other than the main thread results in an implicit call to pthread_exit(), using the function's return value as the thread's exit status. To allow other threads to continue execution, the main thread should terminate by calling pthread_exit() rather than exit(3). The value pointed to by retval should not be located on the calling thread's stack, since the contents of that stack are undefined after the thread terminates. BUGS
Currently, there are limitations in the kernel implementation logic for wait(2)ing on a stopped thread group with a dead thread group leader. This can manifest in problems such as a locked terminal if a stop signal is sent to a foreground process whose thread group leader has already called pthread_exit(). SEE ALSO
pthread_create(3), pthread_join(3), pthreads(7) COLOPHON
This page is part of release 3.44 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/. Linux 2009-03-30 PTHREAD_EXIT(3)
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