How to the return value of main

[amt_muk]

Hello Friendz,

Suppose I have a program like

// A.cpp
int main()
{
     if(some_condition)
          return 1;
     
     return 0;
}

Now from another program I want to run the above program, like

//B.cpp
int main()
{
     ...
     ...
     system("A");
     ...
     ...
     return 0;
}

Here how can I catch the return value of program A from the program B.

Amit

[jencas]

What OS? If Windows try CreateProcess() followed by GetExitCodeProcess():

STARTUPINFO si;
    ZeroMemory(&si, sizeof(si));
    si.cb = sizeof(si);
    PROCESS_INFORMATION pi;
    BOOL bRes = CreateProcess(
        NULL, const_cast<LPSTR>(commandLine), NULL, NULL, FALSE, 0, NULL, NULL, &si, &pi);
    if (bRes) 
    {
        WaitForSingleObject(pi.hProcess, INFINITE);
        DWORD dwExitCode;
        GetExitCodeProcess(pi.hProcess, &dwExitCode);
        CloseHandle( pi.hProcess );
        CloseHandle( pi.hThread );
    }

[amt_muk]

What OS? If Windows try CreateProcess() followed by GetExitCodeProcess():

I am using Solaris.

[Ancient Dragon]

check your man pages for spawn family of functions.

[amt_muk]

check your man pages for spawn family of functions.

Thanx Dragon.
But there is no manual entry for spawn family of functions.

-bash-3.00$ man spawnl
No manual entry for spawnl.
-bash-3.00$

Can u pls suggest some other way to do it.

Amit

[Ancient Dragon]

link and see wait4(). I haven't used these in over 20 years, so you will have to test them out to see how they work.

[Salem]

> system("A");
You may be in luck. Some implementations do the right thing with result = system("A"); The POSIX way would be to use fork(), execl() and wait(), something like

if ( fork() == 0 ) {
  execl()  // run A
} else {
  wait() // wait for A, and get the exit status
}

You'll have to read the manual pages for those functions for actual usage.

[amt_muk]

> system("A");
You may be in luck. Some implementations do the right thing with result = system("A");

Hi Salem,
In my system it is giving 256 times of the actual result.
I am using Studio 11 in Solaris 10 environment.
Can u pls explain it.

Thanx,
Amit

[Salem]

You mean the manual page for system() DOESN'T explain it?

[Duoas]

This is one of those perennial questions...

system() returns the exit code of the command shell (probably bash --or if your system is really old, sh [check your /usr/bin/sh to see if it is a link to bash or not if you want to know]).
Only if your libc was made in an abnormal way will system() execute the program directly.

I've answered this before with a little module. (Alas, it is on another forum.)
Duoas's ExecProcess class
Post size is limited there, so keep scrolling for both files.

If you are new to C++ in general the following link may also be good reading.
Call external program in C++ (Linux) by Hannahlv

Hope this helps.