Re: Can main() return any int value?

James Kanze <>
Sat, 10 Jan 2009 11:52:18 -0800 (PST)
On Jan 10, 2:21 pm, Rolf Magnus <> wrote:

James Kanze wrote:

The meaing of the return value is implementation defined.
The values 0 and EXIT_SUCCESS will be intepreted by the
implementation as sucessful completion of the program,
while EXIT_FAILURE is interpreted an unsucessful completion
of the program. The implementation may ignore the return
value, but must not treat a success case as a failure or
vice versa.

Except that what treating a program as a success is also
implementation defined.

However, if you return any other value the implementation
may interpet it in any way desired by the implementation
creator. In practice this is a non-issue. Most operating
systems treat 0 as success and non-zero as failure,

I'm not sure about most. I don't know of any OS which even
looks at the return code itself.

It depends on what you define as "OS". If you look only at the
kernel, then probaly most don't look at the return code. If
OTOH, you look at the wohle system, things could be different,
probably depending on the type of program you're writing (GUI
program, command line tool, system service, ...).

Yes. What actually comprises the "OS" is a very open question.
In this case, however, you can very well write a program under
Unix or Windows which does something like:

    if ( system( "yourProgram" ) == 0 ) {
        std::cerr << "yourProgram failed" << std::endl ;

It doesn't make sense to do so, but my point is simply that
neither Windows nor Unix require much of anything of the return
code, per se; the "convention" of what is failing and what isn't
is really just that, a convention, and the systems count on the
invoking program to respect it. Most programs delivered with
the system do, when they invoke another program. In the sense
that they're part of the system, the system does judge the
success or failure of your program. But since your program can
also be invoked otherwise, and not all "system" programs look at
the return code, either, there's also a very real sense that the
system doesn't even look at the code. (When I configure a panel
button under KDE to invoke a program, the return code will be
ignored, for example, and I'm pretty sure that the same holds
for configuring an icon on the desktop under Windows.)

Of course, this is not to say that you, as a programmer,
shouldn't care; you want your program to work in all reasonable
contexts. Including cases where the invoking program does look
at the return code.

James Kanze (GABI Software)
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