Returned Code

azaria has asked for the wisdom of the Perl Monks concerning the following question:

I am running a perl script (on Win) which calls C++ exe file, I would like to print out the return value of the C++ exe file

I used -

system("a.exe")
print $?
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either

$retVal = system("a.exe");
print "$retVal\n";
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but both prints:

% C++ retVal : 3
% 256
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Any idea why i get 256 and not 3 ? any solution

___________________________________

C++ code looks -

int main()
{
 cout << "C++ retVal: 3" << endl;
 return 3;
}
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Thanks azaria

Comment on Returned Code Select or Download Code

Replies are listed 'Best First'.
Re: Returned Code by jettero (Monsignor) on Jun 15, 2008 at 10:33 UTC
Check out IPC::System::Simple. It's brand new, but it simplifies stuff like this (and much more). If you check the system page, you'll see that you (probably) need to use the $?... `if ($? == -1) { print "failed to execute: $!\n"; } elsif ($? & 127) { printf "child died with signal %d, %s coredump\n", ($? & 127), ($? & 128) ? 'with' : 'without'; } else { printf "child exited with value %d\n", $? >> 8; }` [download] ... I'm no expert on the topic, and you apparently need to be one, but I think you'll looking for `$? >> 8`. UPDATE: I definitely did think the retval from system() was the same as $?, but the example in the docs showed $?, so that's what I quoted. Really, I was trying to plug IPC::System::Simple and that was my main thesis. I'd like to see that module get really popular. It's neat. If I recall correctly, he (the ISS author) says you do need to check $? for some reason. Maybe I read it on perlbuzz. Maybe I made it up. -Paul	[reply] [d/l] [select]
Re^2: Returned Code by ikegami (Patriarch) on Jun 15, 2008 at 13:43 UTC
If you check the system page, you'll see that you (probably) need to use the $?... `$?` is set to the return value of system are the same thing. I don't see the point of using a global variable when not needed. I think you'll looking for `$? >> 8`. Yes, or `$retVal >> 8`. I don't know why he's getting 256 (Error code 1) instead of 768 (Error code 3), but that's not a Perl issue.	[reply] [d/l] [select]
Re^3: Returned Code by jettero (Monsignor) on Jun 15, 2008 at 16:52 UTC
I don't see the point of using a global variable when not needed. Later in the day, I began to wonder. If it's the same as the return value from system, when is it ever needed? -Paul	[reply]
Re^4: Returned Code by ikegami (Patriarch) on Jun 15, 2008 at 17:01 UTC
Re^2: Returned Code by Anonymous Monk on Jun 15, 2008 at 13:42 UTC
`[nobody@nowhere]$ cat t.cpp #include <iostream> using namespace std; int main() { cout << "C++ retVal: 3" << endl; return 3; } [nobody@nowhere]$ cat t.pl #!/usr/bin/perl system("./a.out"); printf "Got retval: %d\n", $?>>8; [nobody@nowhere]$ ./t.pl C++ retVal: 3 Got retval: 3 [nobody@nowhere]$` [download]	[reply] [d/l]
Re: Returned Code by hilitai (Monk) on Jun 15, 2008 at 13:42 UTC
Could you please add some <code> tags to make your script readable? For example, <code> script goes here </code> UPDATE: I think the reason you're getting the '256' return is because your `system("a.exe");` line is returning an error, not the bit-shifted '3' you are expecting. And I think it's returning an error because system() can't find a.exe, because it's not in your path. Does the return change if you specify `system("./a.exe");` , or otherwise explicitly add in the path to the exe? I'm not on a Windows system, so I can't test your script any more directly.	[reply] [d/l] [select]
Re^2: Returned Code by ikegami (Patriarch) on Jun 15, 2008 at 17:09 UTC
"." is always in the front of the PATH in Windows (implicitly), so if `system("a.exe");` fails, so would `system(".\a.exe");`. (`system("./a.exe");` just plain won't work.) But, that's a good thoery `>perl -e"print system 'nonexistant'" 'nonexistant' is not recognized as an internal or external command, operable program or batch file. 256` [download]	[reply] [d/l] [select]
Re^2: Returned Code by cdarke (Prior) on Jun 16, 2008 at 09:49 UTC
As others have said, the exit value is shifted within the $? variable. This is for historical reasons and compatibility with UNIX. 256 will be returned on an exit code of 1 (one). Incidently, this also means that Perl on Windows places an artificial limit of 0-255 on the exit code. The current directory is the second place searched for executables, the first being the directory from which the calling application was loaded.	[reply]