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AccesDenied
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 Posted: Wed Oct 19, 2005 2:00 am Post subject: use of exit(-1) |
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Can anyone tell me what is use of exit(-1) ..specificaly with with
EXIT_STATUS -1
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Jack Klein
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| Posted: Wed Oct 19, 2005 8:43 am Post subject: Re: use of exit(-1) |
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On 18 Oct 2005 22:00:21 -0400, "AccesDenied" <amit.kamal (AT) gmail (DOT) com>
wrote in comp.lang.c++.moderated:
| Quote: | Can anyone tell me what is use of exit(-1) ..specificaly with with
EXIT_STATUS -1
|
The C language standard, which the C++ standard "inherits" in proper
object oriented fashion, only defines three portable values for
program termination, either by returning from main() or as an argument
to exit():
1. The macro EXIT_SUCCESS defined in <stdlib.h>/<cstdlib>.
2. The macro EXIT_FAILURE defined in <stdlib.h>/<cstdlib>.
3. The value 0.
The result of using 0 is exactly the same as using EXIT_SUCCESS.
The C++ standard, in section 18.3, specifically states:
"Finally, control is returned to the host environment. If status is
zero or EXIT_SUCCESS, an implementation-defined form of the status
successful termination is returned. If status is EXIT_FAILURE, an
implementation-defined form of the status unsuccessful termination is
returned. Otherwise the status returned is implementation-defined."
So if you use any other value as a return from main() or an argument
to exit(), it means whatever your compiler and operating system decide
that it means.
Note on many platforms such as MS-DOS and *NIX, the int value is
truncated to an 8-bit unsigned character so using -1 results in these
systems seeing a value of 255.
--
Jack Klein
Home: http://JK-Technology.Com
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Thomas Maeder
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| Posted: Wed Oct 19, 2005 8:46 am Post subject: Re: use of exit(-1) |
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"AccesDenied" <amit.kamal (AT) gmail (DOT) com> writes:
| Quote: | Can anyone tell me what is use of exit(-1) ..specificaly with with
EXIT_STATUS -1
|
The C and C++ Standards define the symbols EXIT_SUCCESS and
EXIT_FAILURE for signaling success and failure, respectively, to the
outer world. Whether one of them is equal to -1 is unspecified.
So the outcome of using the exit code -1 is application or platform
defined.
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Carl Barron
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| Posted: Wed Oct 19, 2005 8:47 am Post subject: Re: use of exit(-1) |
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In article <1129625968.331879.248280 (AT) g44g2000cwa (DOT) googlegroups.com>,
AccesDenied <amit.kamal (AT) gmail (DOT) com> wrote:
| Quote: | Can anyone tell me what is use of exit(-1) ..specificaly with with
EXIT_STATUS -1
void std::exit(int) terminates the program WITHOUT destructing |
objects of automatic duration. and returning to the system the value of
its argument, [similiar to the return value of main if specified] Beware
exit does not destruct anything on the stack in the calling function or
any of its parent. [6.6 para 2 of jan 2005 draft]. Should be close in
1998 adopted standard.
I don't recommend exit() in new code, a try block in main
catching a specific exception containing the int that would
be passed to exit() [throwing it instead of calling the function
exit(). ] then the cach block could just return the contained
integer from main and all gets destructed properly.
something like this is better C++ code to emulate exit(n)
unless you really do want non destructed objects on quitting.
struct exit_now
{
int ret_val;
exit_now(int a):ret_now(a){}
};
int main()
{
try
{
//....
} catch(exit_now &x)
{
return x.ret_val;
}
return 0;
}
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kanze
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| Posted: Thu Oct 20, 2005 11:20 am Post subject: Re: use of exit(-1) |
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Jack Klein wrote:
[...]
| Quote: | Note on many platforms such as MS-DOS and *NIX, the int value
is truncated to an 8-bit unsigned character so using -1
results in these systems seeing a value of 255.
|
Note too that on Unix and Unix-like, return codes greater than
128 are normally used to indicate that the program was
terminated by a signal.
In portable code, you use EXIT_SUCCESS and EXIT_FAILURE. In
less than portable code, you use values which are common on all
targeted platforms: 0 for success and a small, positive integer
for failure is portable between Unix and Windows, for example.
Internally, I use the following convention:
0 Success, in every sense of the word
1 No error, but not the expected results (e.g. something like
grep matching no lines)
2 An error occured some where during processing.
3 A fatal error occured; processing was interrupted by the
error.
Formally, I also define a 5 for internal errors, but these never
make it to exit -- abort() gets called before then.
These are mapped in an implementation defined manner to the
actual return code; under Unix and Windows, the mapping function
is the identity function, but the default mapping function (for
an unknown system) maps 0 to EXIT_SUCCESS, and everything else
to EXIT_FAILURE.
In practice, this is fairly arbitrary (although the 0/1/2 is
based on Unix grep), and almost all invoking applications will
treat anything but 0 as an error.
--
James Kanze GABI Software
Conseils en informatique orientée objet/
Beratung in objektorientierter Datenverarbeitung
9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34
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Allan W
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| Posted: Thu Oct 20, 2005 11:21 am Post subject: Re: use of exit(-1) |
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Carl Barron wrote:
| Quote: | I don't recommend exit() in new code,
|
Why not?
My own programs typically don't call exit() -- they simply return to
main, which executes return 0. Or, if a critical error is detected,
I call abort(). In cases where I want to control the return value,
I'm likely to use implementation-defined code, returning a value
from 0 to 255 (which can be seen by i.e. BATCH files under
Microsoft Windows).
But this is just the way I happen to organize the program. If I
knew that at a certain point in the code, all processing was 100%
finished, including RAII from statics and globals, I would have
no reason not to call exit.
| Quote: | a try block in main
catching a specific exception containing the int that would
be passed to exit() [throwing it instead of calling the function
exit(). ] then the cach block could just return the contained
integer from main and all gets destructed properly.
something like this is better C++ code to emulate exit(n)
unless you really do want non destructed objects on quitting.
struct exit_now
{
int ret_val;
exit_now(int a):ret_now(a){}
};
|
What is ret_now? I'm sure you mean ret_val.
| Quote: | int main()
{
try
{
//....
} catch(exit_now &x)
{
return x.ret_val;
}
return 0;
}
|
Then the usage would be:
throw exit_now(EXIT_FAILURE);
But I still don't see the advantage.
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Carl Barron
Guest
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| Posted: Thu Oct 20, 2005 5:33 pm Post subject: Re: use of exit(-1) |
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In article <1129738923.947263.51650 (AT) o13g2000cwo (DOT) googlegroups.com>,
Allan W <allan_w (AT) my-dejanews (DOT) com> wrote:
| Quote: | Carl Barron wrote:
I don't recommend exit() in new code,
Why not?
My own programs typically don't call exit() -- they simply return to
main, which executes return 0. Or, if a critical error is detected,
I call abort(). In cases where I want to control the return value,
I'm likely to use implementation-defined code, returning a value
from 0 to 255 (which can be seen by i.e. BATCH files under
Microsoft Windows).
But this is just the way I happen to organize the program. If I
knew that at a certain point in the code, all processing was 100%
finished, including RAII from statics and globals, I would have
no reason not to call exit.
a try block in main
catching a specific exception containing the int that would
be passed to exit() [throwing it instead of calling the function
exit(). ] then the cach block could just return the contained
integer from main and all gets destructed properly.
something like this is better C++ code to emulate exit(n)
unless you really do want non destructed objects on quitting.
struct exit_now
{
int ret_val;
exit_now(int a):ret_now(a){}
};
What is ret_now? I'm sure you mean ret_val.
int main()
{
try
{
//....
} catch(exit_now &x)
{
return x.ret_val;
}
return 0;
}
Then the usage would be:
throw exit_now(EXIT_FAILURE);
But I still don't see the advantage.
The difference is with exceptions the stack unwinds and the objects on |
the stack become destructed as if the block was exited until the catch
clause is found. Exit() is a function call and it just jumps someplace
that exits the process. That is the difference! A big difference if
you
use anything but pointer free pods for automatic objects!
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