READ_DANGLING
Reading from a dangling pointer
Problem
Diagnosis (at runtime)
Repair

READ_DANGLING

Reading from a dangling pointer

This problem occurs when an attempt is made to dereference a pointer that points to a block of memory that has been freed.

Problem

This code attempts to use a piece of dynamically allocated memory after it has already been freed.

	1:	/*
	2:	 * File: readdngl.c
	3:	 */
	4:	#include <stdlib.h>
	5:	
	6:	main()
	7:	{
	8:		char b;
	9:		char *a = (char *)malloc(10);
	10:
	11:		free(a);
	12:		b = *a; 
	13:		return (0);
	14:	}

Diagnosis (at runtime)

	[readdngl.c:12] **READ_DANGLING**
1.	>> 		b = *a;
	
2.		Reading from a dangling pointer: a
	
3.		Pointer:	0x000173e8
4.		In block:	0x000173e8 thru 0x000173f1 (10 bytes)
				block allocated at:
				     malloc() (interface)
				       main() readdngl.c, 9
	
5.				stack trace where memory was freed:
				       main() readdangl.c, 11

		Stack trace where the error occurred:
6.			               main() readdangl.c, 12

1. Source line at which the problem was detected.
2. Description of the problem and the expression that is in error.
3. Value of the dangling pointer variable.
4. Description of the block to which this pointer used to point, including its size, name and the line at which it was allocated.
5. Stack trace showing where this block was freed.
6. Stack trace showing the function call sequence leading to the error.

Repair

Check that the de-allocation that occurs at the indicated location should, indeed, have taken place. Also check that the pointer you are using should really be pointing to a block allocated at the indicated place.

READ_BAD_INDEX

READ_NULL