Check all errors in code?

**Ian Collins** · Sep 19 '08, 08:15 AM

Re: Check all errors in code?

lovecreatesbea. ..@gmail.com wrote:

Do you check all error conditions for all library calls in you code?
>
Is it necessary to check all errors? Is it convenient to check all
errors (or how to make code clean and readable with mass of non
business logic related code block)?
>
The following code from net-snmp library calls atoi five times but
checks none. Do we code a wrapper my_atoi_with_er ror_check() around
atoi and call this new one everywhere else? Is it a good practice (If
it is, why ANSI atoi doesn't do it)?
>

There is no way to check the result of atoi, that's why it's better to
use strtol in most situations.

--
Ian Collins.

**lovecreatesbea...@gmail.com** · Sep 19 '08, 08:25 AM

Re: Check all errors in code?

On Sep 19, 4:08 pm, Ian Collins <ian-n...@hotmail.co mwrote:

lovecreatesbea. ..@gmail.com wrote:

Do you check all error conditions for all library calls in you code?

>

Is it necessary to check all errors? Is it convenient to check all
errors (or how to make code clean and readable with mass of non
business logic related code block)?

>

The following code from net-snmp library calls atoi five times but
checks none. Do we code a wrapper my_atoi_with_er ror_check() around
atoi and call this new one everywhere else? Is it a good practice (If
it is, why ANSI atoi doesn't do it)?

>
There is no way to check the result of atoi, that's why it's better to
use strtol in most situations.

I did not just mean check the return code from a function call.

Especially, I'm asking how to do complicated error check neatly.

**Richard Heathfield** · Sep 19 '08, 08:25 AM

Re: Check all errors in code?

lovecreatesbea. ..@gmail.com said:

Do you check all error conditions for all library calls in you code?

It has been said that you should never check for a condition you don't know
how to handle. But apart from that, check everything.

Is it necessary to check all errors?

Is it useful to know whether your program worked? If not, then the program
itself is probably not all that useful.

The following code from net-snmp library calls atoi five times but
checks none.

Feel free to explain how you'd check atoi. Once you've failed to do that,
you will be in a position to explain why the code is broken.

--
Richard Heathfield <http://www.cpax.org.uk >
Email: -http://www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999

**Ian Collins** · Sep 19 '08, 08:25 AM

Re: Check all errors in code?

lovecreatesbea. ..@gmail.com wrote:

On Sep 19, 4:08 pm, Ian Collins <ian-n...@hotmail.co mwrote:

>lovecreatesbea ...@gmail.com wrote:

>>Do you check all error conditions for all library calls in you code?
>>Is it necessary to check all errors? Is it convenient to check all
>>errors (or how to make code clean and readable with mass of non
>>business logic related code block)?
>>The following code from net-snmp library calls atoi five times but
>>checks none. Do we code a wrapper my_atoi_with_er ror_check() around
>>atoi and call this new one everywhere else? Is it a good practice (If
>>it is, why ANSI atoi doesn't do it)?

>There is no way to check the result of atoi, that's why it's better to
>use strtol in most situations.

>
I did not just mean check the return code from a function call.
>
Especially, I'm asking how to do complicated error check neatly.

Use a language with exceptions :)

--
Ian Collins.

**lovecreatesbea...@gmail.com** · Sep 19 '08, 08:45 AM

Re: Check all errors in code?

On Sep 19, 4:08 pm, Ian Collins <ian-n...@hotmail.co mwrote:

lovecreatesbea. ..@gmail.com wrote:

Do you check all error conditions for all library calls in you code?

>

Is it necessary to check all errors? Is it convenient to check all
errors (or how to make code clean and readable with mass of non
business logic related code block)?

>

The following code from net-snmp library calls atoi five times but
checks none. Do we code a wrapper my_atoi_with_er ror_check() around
atoi and call this new one everywhere else? Is it a good practice (If
it is, why ANSI atoi doesn't do it)?

>
There is no way to check the result of atoi, that's why it's better to
use strtol in most situations.

I ever thought there're errno for atoi also. Thanks for reminder.

**Nick Keighley** · Sep 19 '08, 08:45 AM

Re: Check all errors in code?

On 19 Sep, 09:16, "lovecreatesbea ...@gmail.com"
<lovecreatesbea ...@gmail.comwr ote:

On Sep 19, 4:08 pm, Ian Collins <ian-n...@hotmail.co mwrote:
>

lovecreatesbea. ..@gmail.com wrote:

Do you check all error conditions for all library calls in you code?

>

Is it necessary to check all errors? Is it convenient to check all
errors (or how to make code clean and readable with mass of non
business logic related code block)?

>

The following code from net-snmp library calls atoi five times but
checks none. Do we code a wrapper my_atoi_with_er ror_check() around
atoi and call this new one everywhere else? Is it a good practice (If
it is, why ANSI atoi doesn't do it)?

>

There is no way to check the result of atoi, that's why it's better to
use strtol in most situations.

>
I did not just mean check the return code from a function call.
>
Especially, I'm asking how to do complicated error check neatly.

as someone else suggested, use exceptions.

Out of interest I've coded simple TCP/IP applications
in both C and Python. The Python versions were shorter
and easier to follow.

I somtimes use an exception like style in C

Rv read_box (Db_handle dbh, Box* box, Box_id box_id)
{
Rv rv;
int i;

for (i = 1; i < SHELF_COUNT; i++)
{
if ((rv = read_shelf (dbh, box->shelf[i], box_id, i)) != OK)
return rv;
}

return OK;
}

This was wrappered in macros so the code looked more like:

Rv read_box (Db_handle dbh, Box* box, Box_id box_id)
{
int i;

for (i = 1; i < SHELF_COUNT; i++)
{
read_shelf (dbh, box->shelf[i], box_id, i);
CHECK_ERROR;
}

return OK;
}

It was reasonably easy to follow and reasonably
easy to verify that all the error checking was done.

--
Nick Keighley

"Object-oriented programming is an exceptionally bad idea
that could only have originated in California."
Dijkstra

**lovecreatesbea...@gmail.com** · Sep 19 '08, 08:55 AM

Re: Check all errors in code?

On Sep 19, 4:28 pm, Richard Heathfield <r...@see.sig.i nvalidwrote:

lovecreatesbea. ..@gmail.com said:
>

Do you check all error conditions for all library calls in you code?

>
It has been said that you should never check for a condition you don't know
how to handle. But apart from that, check everything.
>

Sometimes, I omit some error check to come up with a can-work module
rapidly. Those error code will be supplied after some bug report
thrown out. This approach helps to catch up the schedule.

Is it necessary to check all errors?

>
Is it useful to know whether your program worked? If not, then the program
itself is probably not all that useful.
>

Thanks for being patient.

The following code from net-snmp library calls atoi five times but
checks none.

>
Feel free to explain how you'd check atoi. Once you've failed to do that,
you will be in a position to explain why the code is broken.

That snippet is radomly selected. They even do not check the malloc
for three times, see Line 55, 59 and 64 below.

Dude, was it you who wrote atoi piece plus this one?

/* <quote file=../net-snmp-5.4.1.1/agent/auto_nlist.c*/
34 long
35 auto_nlist_valu e(const char *string)
36 {
37 struct autonlist **ptr, *it = 0;
38 int cmp;
39
40 if (string == 0)
41 return 0;
42
43 ptr = &nlists;
44 while (*ptr != 0 && it == 0) {
45 cmp = strcmp((*ptr)->symbol, string);
46 if (cmp == 0)
47 it = *ptr;
48 else if (cmp < 0) {
49 ptr = &((*ptr)->left);
50 } else {
51 ptr = &((*ptr)->right);
52 }
53 }
54 if (*ptr == 0) {
55 *ptr = (struct autonlist *) malloc(sizeof(s truct
autonlist));
56 it = *ptr;
57 it->left = 0;
58 it->right = 0;
59 it->symbol = (char *) malloc(strlen(s tring) + 1);
60 strcpy(it->symbol, string);
61 /*
62 * allocate an extra byte for inclusion of a preceding
'_' later
63 */
64 it->nl[0].n_name = (char *) malloc(strlen(s tring) +
2);
65 #if defined(aix4) || defined(aix5)
66 strcpy(it->nl[0].n_name, string);
67 #else
68 sprintf(it->nl[0].n_name, "_%s", string);
69 #endif
70 it->nl[1].n_name = 0;
71 init_nlist(it->nl);
72 #if !(defined(aix4) || defined(aix5))
73 if (it->nl[0].n_type == 0) {
74 strcpy(it->nl[0].n_name, string);
75 init_nlist(it->nl);
76 }
77 #endif
78 if (it->nl[0].n_type == 0) {
79 if (!
netsnmp_ds_get_ boolean(NETSNMP _DS_APPLICATION _ID,
80
NETSNMP_DS_AGEN T_NO_ROOT_ACCES S)) {
81 snmp_log(LOG_ER R, "nlist err: neither %s nor _
%s found.\n",
82 string, string);
83 }
84 return (-1);
85 } else {
86 DEBUGMSGTL(("au to_nlist:auto_n list_value", "found
symbol %s at %x.\n",
87 it->symbol, it->nl[0].n_value));
88 return (it->nl[0].n_value);
89 }
90 } else
91 return (it->nl[0].n_value);
92 }

/* </quote*/

**Nick Keighley** · Sep 19 '08, 09:25 AM

Re: Check all errors in code?

On 19 Sep, 09:54, "lovecreatesbea ...@gmail.com"
<lovecreatesbea ...@gmail.comwr ote:

On Sep 19, 4:28 pm, Richard Heathfield <r...@see.sig.i nvalidwrote:

lovecreatesbea. ..@gmail.com said:

Do you check all error conditions for all library calls in you code?

>

It has been said that you should never check for a condition you don't know
how to handle. But apart from that, check everything.

>
Sometimes, I omit some error check to come up with a can-work module
rapidly. Those error code will be supplied after some bug report
thrown out. This approach helps to catch up the schedule.

not in my experience! I'd much rather put the checks in at the
beginning.
And if you had the checks you wouldn't need to debug- your program
would tell you what was wrong.

<snip>

--
Nick Keighley

**lovecreatesbea...@gmail.com** · Sep 19 '08, 10:05 AM

Re: Check all errors in code?

On Sep 19, 5:19 pm, Nick Keighley <nick_keighley_ nos...@hotmail. com>
wrote:

On 19 Sep, 09:54, "lovecreatesbea ...@gmail.com"
>
<lovecreatesbea ...@gmail.comwr ote:

On Sep 19, 4:28 pm, Richard Heathfield <r...@see.sig.i nvalidwrote:

lovecreatesbea. ..@gmail.com said:
Do you check all error conditions for all library calls in you code?

>

It has been said that you should never check for a condition you don't know
how to handle. But apart from that, check everything.

>

Sometimes, I omit some error check to come up with a can-work module
rapidly. Those error code will be supplied after some bug report
thrown out. This approach helps to catch up the schedule.

>
not in my experience! I'd much rather put the checks in at the
beginning.
And if you had the checks you wouldn't need to debug- your program
would tell you what was wrong.
>

Yes, your way is right way.

**James Kuyper** · Sep 19 '08, 10:35 AM

Re: Check all errors in code?

lovecreatesbea. ..@gmail.com wrote:

On Sep 19, 4:28 pm, Richard Heathfield <r...@see.sig.i nvalidwrote:

>lovecreatesbea ...@gmail.com said:

....

Sometimes, I omit some error check to come up with a can-work module
rapidly. Those error code will be supplied after some bug report
thrown out. This approach helps to catch up the schedule.

Only in the short term (and not even necessarily in the short term). In
the long run, you'll spend more time dealing with the bug reports and
fixing the problem than it would have taken to do it right in the first
place. Even in the short term, there's a good chance that your can-work
module won't work, and that you'll end up missing your schedule anyway
because of a bug that would have been much easier to track down if you'd
included proper error checking in the first place.

For many years, I held the opinion that if I adequately warn my boss of
the danger of skipping testing for errors, I've met my responsibilitie s.
If he responds by ordering me to go ahead and skip testing despite those
dangers, anything that goes wrong because of that is his responsibility,
not mine. I quickly learned, the hard way, that if I want to take that
attitude, I should always insist on getting such orders in writing. It
took me much longer to learn (again, the hard way) that I should never
obey such orders, period. I don't refuse the orders, I just ignore them.

**James Kuyper** · Sep 19 '08, 10:35 AM

Re: Check all errors in code?

lovecreatesbea. ..@gmail.com wrote:

Do you check all error conditions for all library calls in you code?

For any function call that can fail, I make sure that my code is written
to deal with the possibility that it did fail. That usually means
checking for failure with every function call. However, for things like
writing to a stream, I can do a lot of function calls that write to the
file, and then use ferror() once to see if any of them failed. I almost
never check the return value of printf(), for precisely this reason.

What makes that approach feasible is the fact that, for my typical
program, it doesn't matter much which write to the stream failed; if any
of them failed, it's a fatal error, and there's only a minor cost to
failing late rather than failing immediately. For many people's
programs, that is not true - when writing to a pipe or writing to a
device, it's sometimes important to react immediately to any failure.

This approach is NOT appropriate when reading data from a stream. If the
data was not read in, the contents of the buffer I read it into are
unpredictable, and almost certainly not what the rest of my code expects
it to be. I need to choose an alternate path through my code as soon as
I detect the error.

Is it necessary to check all errors?

No, but it's needed more often than some lazy programmers think it is.
In the long run, it's easier to make a habit of checking every call that
could fail, than to try to figure out for each call whether or not it
really needs to be checked. If you follow the second approach, you'll
almost certainly find yourself debugging a mysterious error that will
end up tracing back to the unnoticed failure of a function call.

... Is it convenient to check all
errors (or how to make code clean and readable with mass of non
business logic related code block)?

No, it is not convenient. There's a real danger of making your code look
like it's main purpose is to produce error messages. I once had a
subordinate who handed me a test plan for a function which triggered
every single error message the function could generate, but which didn't
have even a single test case that didn't generate an error message. His
test plan didn't bother checking whether the program actually performed
the task it was supposed to perform when given non-erroneous input!

**Richard Heathfield** · Sep 19 '08, 11:05 AM

Re: Check all errors in code?

James Kuyper said:

lovecreatesbea. ..@gmail.com wrote:

>Do you check all error conditions for all library calls in you code?

>
For any function call that can fail, I make sure that my code is written
to deal with the possibility that it did fail. That usually means
checking for failure with every function call. However, for things like
writing to a stream, I can do a lot of function calls that write to the
file, and then use ferror() once to see if any of them failed. I almost
never check the return value of printf(), for precisely this reason.

Absolutely - BUT.

But there comes a point of diminishing returns. Let's say you're trying to
write an error message in a dialog box, and the call to display the box
returns an error, which you intercept. Okay, now you have to log it
somewhere else. Let's try stderr! Great - except that the fprintf fails.
Now what do you do?

One might reasonably argue that if we can't even report errors to the user,
the system is so far gone that the only reasonable thing to do is close
the program, returning EXIT_FAILURE as a last ditch effort to be diligent.

--
Richard Heathfield <http://www.cpax.org.uk >
Email: -http://www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999

**pete** · Sep 19 '08, 11:45 AM

Re: Check all errors in code?

lovecreatesbea. ..@gmail.com wrote:

Do you check all error conditions for all library calls in you code?

Not if I don't have any alternative action that I want to perform.
If printf("hello world\n") returns EOF,
then I really don't have any alternative action for that.

--
pete

**James Kuyper** · Sep 19 '08, 12:15 PM

Re: Check all errors in code?

pete wrote:

lovecreatesbea. ..@gmail.com wrote:

>Do you check all error conditions for all library calls in you code?

>
Not if I don't have any alternative action that I want to perform.
If printf("hello world\n") returns EOF,
then I really don't have any alternative action for that.

Even if all other modes of reporting an error are shut down, you can
always exit with an exit status of EXIT_FAILURE. That method of
reporting might be disabled too, but there's no way from within portable
code to determine that, so you might as well try.

Check all errors in code?

Check all errors in code?

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