Jan

How can I get what my main function has returned in Linux?

JIGAR PATEL Category

In a C program if we want to give some input from terminal then we can give it by:

int main(int argc, char *argv[])

In the same way, if we want to get return value of main() function then how can we get it?

In each main() we write return 1 or return 0; how can we know what my main() has returned at terminal?

#include<stdio.h>
int main()
{
printf("Share Programing Tips");
return 32;
}

Now save this program as test.c file and in terminal run following command

$ gcc test.c
 
$ ./a.out
 
$ echo $?  // this will show the return value of main

Most shells store the exit code of the previous run command in $? so you can store or display it.

A C program always has an exit code, which the program may decide for itself if it terminates normally, by returning a value from the main function or by calling the exit function. If the program terminates abnormally, for example by a segmentation fault, the operating system decides the exit code.

In Unix (Posix), the exit code is an 8-bit value: 0-255. It is combined with some other metadata to a status: the other metadata includes information about whether the program terminated normally or not, if it was terminated because of a signal, and if so, which signal. For details, see the wait(2) manual page.

In Unix, at the shell, the status of the previous command is accessible as the $? special variable. Because the exit code is only 8 bits, and it’s treated as an unsigned integer, if you return a negative value, it gets turned into a positive one: -1 becomes 255. Likewise, if you return a value greater than 255 only the least significant 8 bits are used: 256 becomes 0.

You can use this return code in linux script file.

JIGAR PATEL

hey I am an Artist who love to write code…! Well I am an EC graduate From Ganpat University and now i am working as Embedded software engineer in one private firm.. find me at here JigAr Patel

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