Why is char *p =s; valid?

[KnRfan]

Hi,

I learned a bit of C a few years ago, but since it was not for one of my university courses(a bit of C++ and quite a bit more Java, Python and C#) my study of the language did not go all that far, so I apologize if my questions sounds like total noob lunacy, I merely wish to rectify the huge mystake of not really learning C.

So I was browsing some code, and basically address assignment here is done at pointer declaration, however since the '*' character is also used for dereferencing as well is it not more proper to first declare the pointer, and only then to assign it something to point to, like this:

char *p;
p=s;

instead of char *p=s:

Shouldn't that be more clear and safe, can somebody please explain the rational behind this type of assignment to me?

[Alpo]

At it's declaration though, it wouldn't really make sense for the pointer to be dereferenced in an assignment. It isn't pointing to anything yet, so you couldn't modify the value of anything it points to at that time. It does look a little like dereference though, that's why I always write a declaration of a pointer like this:

    char* p; // It looks clearer that the identifier p is pointer to char

Everyone does it a little different, the worst looking to me is this :

    char * p; // I see this in books sometimes, and always immediately think multiplication is going on lol.

[rstanley]

In the following overly simplified example, I have defined a pointer to char called s, and initialized it to the address of the first character of a constant string;

#include <stdio.h>
int main(void)
{
   char *s = "Hello World.";      /* s is a pointer to a constant string. */

   char *p = s;                  /* p is a pointer to a char and inistialized
                                    with the value of s  */

   printf("%c\n", *p);            /* Print the first character of the string using p  */

   return 0;
}

I have then defined another pointer to a char called p, and initialized the pointer with the address that is stored in the pointer, s. The '*' in both cases define both p & s as pointers.

The printf() statement uses the '*' to dereference the pointer to print the first character of constant string.

The '*' is used to both declare/define, AND dereference in different contexts.

You need to study arrays and pointers to gain a better understanding.

[KnRfan]

In the following overly simplified example, I have defined a pointer to char called s, and initialized it to the address of the first character of a constant string;

#include  int main(void) {    char *s = "Hello World.";      /* s is a pointer to a constant string. */     char *p = s;                  /* p is a pointer to a char and inistialized                                     with the value of s  */     printf("%c\n", *p);            /* Print the first character of the string using p  */     return 0; }

I have then defined another pointer to a char called p, and initialized the pointer with the address that is stored in the pointer, s. The '*' in both cases define both p & s as pointers. The printf() statement uses the '*' to dereference the pointer to print the first character of constant string. The '*' is used to both declare/define, AND dereference in different contexts. You need to study arrays and pointers to gain a better understanding.

Yeah, I got that, I am just saying that maybe both declaring and assigning might not be the best idea where pointer are concerned, I was merely wondering why such misleading syntax was allowed in the first place. Thanks for your replies.

[laserlight]

I am just saying that maybe both declaring and assigning might not be the best idea where pointer are concerned, I was merely wondering why such misleading syntax was allowed in the first place.

It is not misleading once you recognise that it is an initialisation done at the point of declaration rather than an assignment done after the declaration. Furthermore, while many times this initialisation might be for convenience, if you have a pointer that is const, you will need to do such initialisation since you cannot validly assign to the pointer later.

char* p; // It looks clearer that the identifier p is pointer to char

I recommend reading Stroustrup's answer to the FAQ: Is ``int* p;'' right or is ``int *p;'' right?

[rstanley]

Yeah, I got that, I am just saying that maybe both declaring and assigning might not be the best idea where pointer are concerned, I was merely wondering why such misleading syntax was allowed in the first place. Thanks for your replies.

I always initialize my variables to some appropriate value, and all my pointers to a valid address or NULL. For example:

int count = 0;
char *ptr = NULL;
//etc...

Why do either one as two statements, when one will define and assign in both examples? The compiler is probably creating the same code in both cases. I find the definition, and initialization as one statement to be more clear. If two statements would be more clear to you then by all means do so.