realloc problems

I use realloc to find a new memory location assign it to a pointer and copy its old data to the new location. I get NULL. I tryed to use MessageBox and itoa functions to find out the new size in bytes witch is 24bytes. I don't know why it returns NULL. I used malloc previously to allocate a poniters starting memory. Here is the line that returns NULL;

Lines.lpLines =(char **)realloc(Lines.lpLines, sizeof(char **) * Lines.max );

Anyone know what the problem could be?

Thanx in advance!

Any prior use of malloc/realloc/free could have messed things up
Any prior use of the memory returned by malloc/realloc could have messed things up here

Look for
- use before alloc
- use after free
- generally getting the size wrong - int *ptr = malloc(10) does NOT allocate space for 10 integers.

Also, your code has the realloc assignment bug

Code:

---

char **temp = (char **)realloc(Lines.lpLines, sizeof(char **) * Lines.max );
if ( temp != NULL ) {
    Lines.lpLines = temp;
} else {
    // cannot realloc
    // but at least Lines.lpLines points to what we have so far
}

---

Use a temp pointer to preserve the old pointer, until you know the new one is allocated.

You really should be using new and delete in C++.

Thanx. I got it to work properly using new and delete.