another c pointer question

Member

Posts: 194
Joined: 2009.02

Post: #1

Mar 25, 2010 — 12:45 PM

Code:

char *c = malloc(255);

if (c != NULL)

{

        strcpy(c, "Hello world!");

}

void *ptr = c;

char *c2 = ptr;

It appears to work, but is it safe? Does the void pointer throw out information pertaining to the number of elements pointed to, or does it simply overlook it, thus allowing c2 access to it(the number of elements) once again?

Skorche

Sage

Posts: 1,478
Joined: 2002.09

Post: #2

Mar 25, 2010 — 01:38 PM

Pointers don't know anything about sizes of the things that they point to. That's why you can put a pointer into the middle of an array if you want.

What's really happening here is that C strings are null terminated strings. This means that the string "the" is actually 4 characters long. -> 't', 'h', 'e' followed by a zero. To find the length of a string, you actually have to check each character until you find a zero in it.

Scott Lembcke - Howling Moon Software
Author of Chipmunk Physics - A fast and simple rigid body physics library in C.

NelsonMandella

Member

Posts: 194
Joined: 2009.02

Post: #3

Mar 25, 2010 — 02:51 PM

Thanks, I always get so confused when dealing with c strings.

DoG

Moderator

Posts: 869
Joined: 2003.01

Post: #4

Mar 26, 2010 — 03:49 AM

You typically should to use strncpy() instead of strcpy() to prevent buffer overruns.

Don't panic.

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