Synopsis

Freeing a memory location more than once.

Enabled by default

Yes

Severity/Certainty

High/Medium

Full description

An attempt is made to free a memory location after it has already been freed. This will most likely cause an application crash. Unlike MEM-double-free, MEM-double-free-alias examines the location that pointers point to instead of the pointers themselves. You might see reports for code that looks like this (example of a linked list where each node has a pointer to an element, elem): for (; list != NULL; list = list->next) { free(list->elem); } The warning is issued because there is no guarantee that each list node's elem field is the same.

Coding standards

Code examples

The following code example fails the check and will give a warning:

#include <stdlib.h>
void f(int *p) {
  free(p); 
  if(p) free(p); 
}

The following code example passes the check and will not give a warning about this issue:

#include <stdlib.h>

void example(void) 
{
  int *p=malloc(4);
  free(p);
}