Main Content

MISRA C:2023 Rule 22.2

A block of memory shall only be freed if it was allocated by means of a Standard Library function

Since R2024a

expand all in page

Description

Rule Definition

A block of memory shall only be freed if it was allocated by means of a Standard Library function.

Rationale

The Standard Library functions that allocate memory are malloc, calloc and realloc.

You free a block of memory when you pass its address to the free or realloc function. The following causes undefined behavior:

  • You free a block of memory that you did not allocate.

  • You free a block of memory that have already freed before.

Polyspace Implementation

You can check for this rule with a Bug Finder analysis only.

Troubleshooting

If you expect a rule violation but do not see it, refer to Diagnose Why Coding Standard Violations Do Not Appear as Expected.

Examples

expand all

#include <stdlib.h>

void func1(void) {
    int x=0;
    int *ptr=&x;

    free(ptr); /* Non-compliant: ptr is not dynamically allocated */
   
}

In this example, the rule is violated because the free function operates on a pointer that does not point to dynamically allocated memory.

#include <stdlib.h>

void func(int arrSize) {
    int *ptr = (int*) malloc(arrSize* sizeof(int));
   
    free(ptr);   /* Block of memory freed once */
    free(ptr);   /* Non-compliant - Block of memory freed twice */
}

In this example, the rule is violated when the free function operates on ptr twice without a reallocation in between.

Check Information

Group: Resources
Category: Mandatory
AGC Category: Mandatory

Version History

Introduced in R2024a

See Also

| | | |

Topics