In this section:

Overview

This error is generated if the null pointer is passed to a routine that de-allocates memory.

Code	Description	Enabled	Reported	Platform
FREE_NULL	Freeing null pointer		Runtime	Windows/Unix

Problem

The following code attempts to free a null pointer:

/*
 *File: freenull.c
 */
char*a;

main()
{
	free(a);
	return 0;
}

Diagnosis at Runtime

[freelocl.c:8] **FREE_LOCAL**
>>		free(a);
Freeing null pointer: a

---- Associated Common Weakness Enumerations ----
CWE-476: Null pointer dereference

Stack trace where the error occurred
		main() freenull.c8
**Memory corrupted. Program may crash!!**

• Line 2: Source file and line at which the problem was detected.
• Line 3: Description of the problem and the expression that is in error.
• Line 5-6: CWE associated with this problem.
• Line 8: Stack trace showing the function call sequence leading to the error.
• Line 10: Informational message indicating that a serious error has occurred which may cause the program to crash.

Repair

The quick, simple solution is to add code to check whether the pointer is null before calling free(). Alternatively, check the stack trace. Doing so can lead to clues as to how the pointer was set to null in the first place, so that the error can be prevented from the root.

References

The table below shows Common Weakness Enumerations associated with this error.