about realloc

[bartleby84]

Hello!

I have some doubts about "realloc". I've read the man file but I'm not sure about a few of things:

- Does realloc initializate (I'm spanish I don't know if it is well write) the new space of memory??
- If I use realloc like this:

ptr = calloc(50,sizeof(char));
ptr = realloc(ptr, 100);

Then ptr will point to the new allocated memory or to the first positon of the array??

Thank you for your help

[itsme86]

Does realloc initializate (I'm spanish I don't know if it is well write) the new space of memory??

No. The allocated memory will contain whatever random garbage was in it before realloc() was called.

Then ptr will point to the new allocated memory or to the first positon of the array??

It will point to the beginning of the array.

[Salem]

> Does realloc initializate (I'm spanish I don't know if it is well write) the new space of memory??
The smaller of the 'old size' or the 'new size' is preserved.

> ptr = realloc(ptr, 100);
Don't assign the result to the same pointer. If realloc fails, it returns NULL, but the old memory is NOT freed (but you have lost the pointer to it, so it is a leak).
Always do something like

void *temp = realloc( ptr, 100 );
if ( temp != NULL ) {
    // success
    ptr = temp;
} else {
    // some error action
    free( ptr );
}