CODEWITHSUNDEEP
c++cmemory-leaks
jamk
jamk

Reputation: 866

Comprehension issue with the delete[] operator used on c++ arrays

Hello I know that in C if I do the following I will get a memory leak:

int *b = malloc(128*sizeof(int));
b = b+25;
free(b);

Now I was trying to understand if the new[] and the delete[] operators have the same problem or not. Would I get a memory leak if I write the following ?

int* bcpp = new int[128];
bcpp +=25;
delete[] bcpp;

Upvotes: 0

Views: 78

Answers (2)

Deduplicator
Deduplicator

Reputation: 45654

7.22.3.3 The free function

#include <stdlib.h>
void free(void *ptr);

2 The free function causes the space pointed to by ptr to be deallocated, that is, made available for further allocation. If ptr is a null pointer, no action occurs. Otherwise, if the argument does not match a pointer earlier returned by a memory management function, or if the space has been deallocated by a call to free or realloc, the behavior is undefined.
3 The free function returns no value.

Passing a pointer to delete [] which does not come from new [] in C++ has the same adverse effect as passing a pointer to free which does not come from a corresponding allocation function in C and C++.

Upvotes: 2

Baum mit Augen
Baum mit Augen

Reputation: 50053

free or delete[] must be invoked on pointers returned by malloc or new[] or on a nullptr. If invoked on anything else, your program has undefined behavior.

This means that in both your examples, you could get a leak or a free pizza or whatever, everything is legal.

An example for a leak in C++ would be the following:

void fun () {
    int* p = new int[128];
}

Now you have no way to delete p, so the memory pointed to by p is leaked.

Upvotes: 3

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