Derek Martin wrote:
> On Mon, Oct 31, 2005 at 01:30:44PM -0600, STYMA, ROBERT E (ROBERT) wrote:
>
>>The syntax:
>>int main(int argc, char **argv)
>>works, but most of the C books I have seen recommend
>>the *argv[] version.
>
>
> I meant to comment that these two different notations are functionally
> identical; an array name is nothing more than a pointer. For example,
> if we have the following code:
Not true. Or rather, only partially true.
In a variable declaration the two are *not* equivalent. In a parameter
declaration and in an expression, the two *are* equivalent.
The difference is, in a variable declaration, you also specify how much
space is to be allocated for the variable, which is not the case for the
other uses.
So, the books are indeed correct, **argv and *argv[] are equivalent
*when used in the parameter list*.
>
> #include <stdio.h>
> void main (void){
>
> char foo[] = "This is a string\n";
And this is totally different from
char *foo = "This is a string\n";
The former declares an array and gives it a name, the latter declares an
anonymous array (string) and creates a pointer to it. With the former
declaration, you cannot alter the value of foo, with the latter you can
(alter as in foo = some_other_value; or foo++;).
> char *bar = foo;
>
> /* these expressions all print "T\n" */
> printf("%c\n", foo[0]);
> printf("%c\n", *bar);
> printf("%c\n", bar[0]);
> printf("%c\n", *foo);
>
> /* these expressions all print "i\n" */
> printf("%c\n", foo[2]);
> printf("%c\n", *(bar + 2));
> printf("%c\n", bar[2]);
> printf("%c\n", *(foo + 2));
> }
>
> The results may surprise programming students:
>
> $ gcc -o ptr ptr.c
> ptr.c: In function `main':
> ptr.c:2: warning: return type of 'main' is not `int'
> [ddm@archonis ~]
> $ ./ptr
> T
> T
> T
> T
> i
> i
> i
> i
>
>
> In reality, foo[x] is just "syntactic sugar" for *(foo + x). This
> is called pointer math, and works properly regardless of the size and
> type of foo, so long as it was declared properly before being used.
>
> [I'm very bored today...]
>
>
--
Sjoerd Mullender
Attachment:
signature.asc
Description: OpenPGP digital signature
