senseless statement?

[Tobias Blass]

Hi all,
I'm just reading fetchmail source code and found the following lines
/* env.c, line 37 */
void envquery(int argc,char **argv)
{
/* ... */
(void)argc;
(void)argc;
/*...*/
}

envquery is called (from main()) like this

envquery(argc,argv);

I don't really get the sense of these two (void)argc; . Does this have
any special meaning or is it really "take the value of argc and ignore
it"?

 

[Ian Collins]

Hi all,
I'm just reading fetchmail source code and found the following lines
/* env.c, line 37 */
void envquery(int argc,char **argv)
{
/* ... */
(void)argc;
(void)argc;
/*...*/
}

envquery is called (from main()) like this

envquery(argc,argv);

I don't really get the sense of these two (void)argc; . Does this have
any special meaning or is it really "take the value of argc and ignore
it"?

Yes, probably to silence an over enthusiastic compiler of lint.

It's a shame C hasn't embraced C++'s use of unnamed parameters.

 

[Ian Collins]

Yes, probably to silence an over enthusiastic compiler of lint.

Make that "compiler *or* lint".

 

[Ike Naar]

void envquery(int argc,char **argv)
{
/* ... */
(void)argc;
(void)argc;
/*...*/
}

envquery is called (from main()) like this

envquery(argc,argv);

I don't really get the sense of these two (void)argc; . Does this have
any special meaning or is it really "take the value of argc and ignore
it"?

Probably a way to suppress compiler warnings for 'unused parameter'.

 

[Ben Bacarisse]

I'm just reading fetchmail source code and found the following lines
/* env.c, line 37 */
void envquery(int argc,char **argv)
{
/* ... */
(void)argc;
(void)argc;
/*...*/
}

envquery is called (from main()) like this

envquery(argc,argv);

I don't really get the sense of these two (void)argc; . Does this have
any special meaning or is it really "take the value of argc and ignore
it"?

That's pretty much what it does. So does

argc;
argv;

with no casts but a compiler is more likely to complain about that and I
guess whole point is to suppress a warning about argc and argv being
unused. Guessing some more, I would suppose that envquery is passed
argc and argv because there might have been a plan to use them in the
future, or because some versions of the function do and some don't (if
there are conditionally compiled sections in the function for example).

 

[Tobias Blass]

Make that "compiler *or* lint".

But what should lint complain about, resp. why doesn't lint complain
any more if you add (void)argc?

 

[Tobias Blass]

That's pretty much what it does. So does

argc;
argv;

with no casts but a compiler is more likely to complain about that and I
guess whole point is to suppress a warning about argc and argv being
unused. Guessing some more, I would suppose that envquery is passed
argc and argv because there might have been a plan to use them in the
future, or because some versions of the function do and some don't (if
there are conditionally compiled sections in the function for example).

You're right, it seems that argc is never used later in the function
(just argv). Thanks for your fast reply
(When I posted the other message with the question what lint should complain
about I haven't seen this reply yet. You can ignore it)

 

[Johannes Schaub (litb)]

Hi all,
I'm just reading fetchmail source code and found the following lines
/* env.c, line 37 */
void envquery(int argc,char **argv)
{
/* ... */
(void)argc;
(void)argc;
/*...*/
}

envquery is called (from main()) like this

envquery(argc,argv);

I don't really get the sense of these two (void)argc; . Does this have
any special meaning or is it really "take the value of argc and ignore
it"?

Noone has yet pointed out that only the first (void)argc; really is useful.
The second (void)argc; is really without sense. I suspect that's a typo, and
the second one should be (void)argv;.

 

[Tobias Blass]

Noone has yet pointed out that only the first (void)argc; really is useful.
The second (void)argc; is really without sense. I suspect that's a typo, and
the second one should be (void)argv;.

This wouldn't make sense either, since argv is used in the function in every
case (not only in possible #ifdef branches or something). You can see it in the
fetchmail source code if you wannt to see it 8I don't want to post the entire
100 lines function here)

 

[Keith Thompson]

This wouldn't make sense either, since argv is used in the function in every
case (not only in possible #ifdef branches or something). You can see it in the
fetchmail source code if you wannt to see it 8I don't want to post the entire
100 lines function here)

So it's a (harmless) error in the fetchmail source. If neither argc nor
argv were used, it would make sense to have

(void)argc;
(void)argv;

Since argv is used but argc isn't, it would make sense to have:

(void)argc;

There's no particular reason for the compiler to warn about it, so it
was missed.