Another pointer question

[Pino]

I have a questing about pointers. When I initialize a pointer using

char * crap_ptr = "crappy pointer"

I can't modify it for example using strcat, I have the same problem with the following example

int somefunction(char * some_ptr)
{
    strcat(some_ptr, "hmm");
    return 0;
}

somefunction("error"); /* will generate fatal error */

I'm guessing its because they are part of the program itself and located in the stack and malloc allocates heap memory.

So I was hoping if someone could tell me if I'm right or not

[Salem]

"strings" are usually stored in read-only memory, so trying to modify them usually results in a crash.

If your compiler makes "strings" constant, they're usually placed in the same part of memory as your compiled code.

[Sebastiani]

>> If your compiler makes "strings" constant, they're usually placed in the same part of memory as your compiled code.

static data doesn't have execute permission though, I wouldn't expect to find them in the same section per se.

[Kleid-0]

You're trying to modify a char array that's a constant:

char *myString = "Hello";

Is the Same thing as:

const char BLAH[] = "Hello";
char *myString = BLAH;

You should do this instead, so you can modify the contents:

char myString[] = "Hello";
myString[0] = 'P';

OR

char *myString = malloc(255 * sizeof(*myString));  /* Create 255 characters of space */
strcpy(myString, "Hello");
myString[0] = 'P';

[quzah]

When illustrating the use of malloc, it's best to remeber it's always used with it's companion function, free.

Quzah.

[Kleid-0]

I always forget free, ggrraahh!

[Pino]

Thanks a lot guys, the problem was I used this to test functions etc. So I'll just stick to strcpy first like Kleid-0 described.