where does /return value/ go?

[arnuld]

1.) we usually say /return 0/ indicates success e.g

#include <iostream>

int main() {
int i=3;

std::cout << i << std::endl;

return 0;
}


i ran the programme & i see only /3/ as output. i dont see any /0/ on
my terminal. where does it go? & who reads /0/ to indicate success?

[Steve Pope]

Re: where does /return value/ go?

arnuld <arnuld3@gmail. comwrote:

>1.) we usually say /return 0/ indicates success e.g
>
>#include <iostream>
>
>int main() {
int i=3;
>
std::cout << i << std::endl;
>
return 0;
>}
>
>
>i ran the programme & i see only /3/ as output. i dont see any /0/ on
>my terminal. where does it go? & who reads /0/ to indicate success?

Programs such as shells and make utilities can see and use the return
value of a program. A user executing the program from the command
line does not usually see it.

You'll have to look at your operating system documentation to
learn more.

Steve

[Gianni Mariani]

Re: where does /return value/ go?

arnuld wrote:

1.) we usually say /return 0/ indicates success e.g
>
#include <iostream>
>
int main() {
int i=3;
>
std::cout << i << std::endl;
>
return 0;
}
>
>
i ran the programme & i see only /3/ as output. i dont see any /0/ on
my terminal. where does it go? & who reads /0/ to indicate success?

If you executed your program from the std::system function call then the
value is partly returned by the system call. If the return value from
system() is negative then there was an error, otherwise the lower 8 bits
are the lower 8 bits returned from main often termed the "status".

Other facilities like "pclose", createprocess, waitpid, etc also enable
getting at the "status" in the same way.

The convention is to return 0 if the program was "successful " and non
zero otherwise. I a compiler finds an error, it is expected that the
return status is "1". For example, in the "sendmail" the mail system,
if the program has a "temporary" error, the return status should be "75"
or sometimes termed EX_TEMPFAIL.

see:

http://www.google.com/codesearch?q=+EX_TEMPFAIL+show:h8zMCqN8hY8:MGccfiUknTg:aYjBDUSBcpI&sa=N&cd=1&ct=rc&cs_p=http://www.opensource.apple.com/darwinsource/tarballs/other/passwordserver_sasl-59.3.tar.gz&cs_f=passwordserver_sasl-59.3/cyrus_sasl/include/exits.h#a0

You almost never have to worry about anything other than "0" - success,
or "1" failure.

[Jacek Dziedzic]

Re: where does /return value/ go?

arnuld wrote:

1.) we usually say /return 0/ indicates success e.g
>
#include <iostream>
>
int main() {
int i=3;
>
std::cout << i << std::endl;
>
return 0;
}
>
>
i ran the programme & i see only /3/ as output. i dont see any /0/ on
my terminal. where does it go? & who reads /0/ to indicate success?

<OT>
Your command shell took it. Usually you'll have an OS-specific
means to check the return value, e.g. in a bash shell under
linux you may try, assuming your program executable is named a.out

#!/bin/bash
../a.out
echo "The return value is $?"

</OT>

HTH,
- J.

[Default User]

Re: where does /return value/ go?

Gianni Mariani wrote:

If you executed your program from the std::system function call then
the value is partly returned by the system call. If the return value
from system() is negative then there was an error, otherwise the
lower 8 bits are the lower 8 bits returned from main often termed the
"status".

There is no such requirement for the system() function. From the C99
draft standard:

7.20.4.5 The system function

Synopsis

[#1]

#include <stdlib.h>
int system(const char *string);

Description

[#2] If string is a null pointer, the system function
determines whether the host environment has a command
processor. If string is not a null pointer, the system
function passes the string pointed to by string to that
command processor to be executed in a manner which the
implementation shall document; this might then cause the
program calling system to behave in a non-conforming manner
or to terminate.

Returns

[#3] If the argument is a null pointer, the system function
returns nonzero only if a command processor is available.
If the argument is not a null pointer, and the system
function does return, it returns an implementation-defined
value.





Brian