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int main(int argc, char *argv[] ) vs int main(int argc, char **argv )

Is this a style thing?

int main(int argc, char *argv[] ) or int main(int argc, char **argv )

i.e. *argv[] or **argv

Why choose the latter?
Nov 14 '05
14 39821
Peter Nilsson wrote:
Sidney Cadot <si****@jigsaw. nl> wrote in message news:<bu******* ***@news.tudelf t.nl>...
August Derleth wrote:

[...snip...]

int crc32(char *buf, int len);

Would compute the 32-bit cyclical redundancy check of a buffer
containing character values.


Wouldn't it be more appropriate if the return type was unsigned? The
resulting value denotes a polynome with binary coefficients, and there
is nothing to justify a special meaning for the sign bit.

Forthermore , if you use signed ints inside the routine, you are going to
do bitwise operations on signed numbers, which may give headaches
concerning portability.

(By pretty much the same token, I'd make the buf's base type an unsigned
char.)

I'd shoot for...

unsigned long crc32(const void *, size_t);


That, indeed, would be favorite.

--
My address is yvoregnevna gjragl-guerr gjb-gubhfnaq guerr ng lnubb qbg pbz
Note: Rot13 and convert spelled-out numbers to numerical equivalents.
Nov 14 '05 #11
John L wrote:
The important thing is to distinguish between pointers
to pre-existing arrays, and pointers which will have
space allocated to them inside the function, and cases
somewhere between the two. But C provides no way of doing
this, and half the time the documentation is no help either. :-(

John.


I agree totally, and I do include fairly large and complete block
comments in my header files that give an indication of what my function
expects, what it will do if those conditions are not met (assuming my
function can tell), and what it will do if everything is nominal.

The rest, as they say, relies on the kindness of strangers.

--
My address is yvoregnevna gjragl-guerr gjb-gubhfnaq guerr ng lnubb qbg pbz
Note: Rot13 and convert spelled-out numbers to numerical equivalents.
Nov 14 '05 #12
Richard Heathfield <do******@addre ss.co.uk.invali d> spoke thus:
I prefer **, but some
prefer *[], and with perfectly sound reasoning for their preference, so who
am I to tell them they're wrong?


Well, considering you've co-written a book and "they" probably haven't,
maybe your style preferences count a little bit more ;)

--
Christopher Benson-Manica | I *should* know what I'm talking about - if I
ataru(at)cybers pace.org | don't, I need to know. Flames welcome.
Nov 14 '05 #13
In <40********@127 .0.0.1> "Hal Styli" <no_spam@all> writes:
Is this a style thing?

int main(int argc, char *argv[] ) or int main(int argc, char **argv )
Yes.
i.e. *argv[] or **argv

Why choose the latter?


1. Because it's the *actual* type of argv, *argv[] is merely syntactic
sugar.

2. Because it saves one keystroke.

To the newbie, *argv[] is more intuitive, because it actually reflects
the common usage of argv. That's why most C books use this notation.

Once the programmer realises that *argv[] is nothing more than syntactic
sugar for **argv (which is far from obvious to the newbie), the easier
to type form may become more attractive.

Note that this discussion is valid only for argv when used as function
parameter. In any other context, the two forms have different meanings:

char **foo; /* a pointer to a pointer to char */
char *bar[]; /* an array of pointers to char, of unspecified size */

foo has a complete type, i.e. its size is known by the compiler, and
therefore sizeof foo is OK anywhere after the declaration of foo.

bar has an incomplete type, its size is not known until another
declaration will specify the actual number of array elements:

fangorn:~/tmp 144> cat test.c
char *bar[];

int invalid(void) { return sizeof bar; }

char *bar[3];

int main(void) { return sizeof bar; }
fangorn:~/tmp 145> gcc test.c
test.c: In function `invalid':
test.c:3: sizeof applied to an incomplete type

While this is a contrived example, it is not uncommon to have declarations
of external arrays of unknown size:

extern *bar[];

bar is actually defined in another module and there is no way to tell its
number of elements at compile time. At run time, either the module
defining it will export its size to the rest of the program or a sentinel
value will be used to mark the end of the array (or both, for partially
initialised arrays).

Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Da*****@ifh.de
Nov 14 '05 #14
> >Is this a style thing?

int main(int argc, char *argv[] ) or int main(int argc, char **argv )


Yes.

Note that this discussion is valid only for argv when used as function
parameter. In any other context, the two forms have different meanings:

char **foo; /* a pointer to a pointer to char */
char *bar[]; /* an array of pointers to char, of unspecified size */


Actually, the discussion is valid for any function parameter, eg if:
void baz(char *bar[])
then sizeof(bar) == sizeof(char **). Same goes for:
void baz(char *bar[9])
or any other subscript.
Nov 14 '05 #15

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