In this section:

Overview

This problem occurs when an attempt is made to dereference a pointer whose value is invalid or that Insure++ did not see allocated. There are several causes of this problem:

• Errors in user code that result in pointers that don’t point at any known memory block.
• Compiling only some of the files that make up an application. This can result in Insure++ not knowing enough about memory usage to distinguish correct and erroneous behavior.

This section focuses on the first type of problem described here. For information about the second type of problem, contact Parasoft’s Quality Consultants.

Code	Description	Enabled	Reported	Platform
WRITE_WILD	Writing to a wild pointer		Runtime	Windows/Unix

Problem 1

The following code attempts to use the address of a variable but contains an error at line 8 - the address operator (&) has been omitted.

/*
 * File: writwld1.c
 */
main()
{
	int i = 123, *a;

	a = i;
	*a = 99;
	return (0);
}

Diagnosis at Runtime

[writwld1.c:9] **WRITE_WILD**
>>		 *a = 99;
Writing to a wild pointer: a
Pointer : 0x0000007b
Stack trace where the error occurred:
			main() writwld1.c, 9

• Line 2: Source line at which the problem was detected.
• Line 3: Description of the problem and the name of the parameter that is in error.
• Line 4: Value of the bad pointer.
• Line 5: Stack trace showing the function call sequence leading to the error.

Most compilers will generate warning messages for this error because the assignment in line 8 uses incompatible types.

Problem 2

Another version of the same problem can occur when using union types. The following code first assigns the pointer element of a union but then overwrites it with another element before using it.

/*
 * File: writwld2.c
 */
union {
	int *ptr;
	int ival;
} u;

main()
{
	int i = 123;

	u.ptr = &i;
	u.ival = i;
	*u.ptr = 99;
	return (0);
}

This code will not generate compile time errors.

Diagnosis at Runtime

[writwld2.c:15] **WRITE_WILD**
>>		 *u.ptr = 99;
Writing to a wild pointer: u.ptr
Pointer : 0x0000007b
Stack trace where the error occurred:
			main() writwld2.c, 15

• Line 2: Source line at which the problem was detected. 
• Line 3: Description of the problem and the name of the parameter that is in error.
• Line 4: Value of the bad pointer.
• Line: 5: Stack trace showing the function call sequence leading to the error. 

Repair

The simpler types of problems are most conveniently tracked in a debugger by stopping the program at the indicated source line. You should then examine the illegal value and attempt to see where it was generated. Alternatively, you can stop the program at some point shortly before the error and singlestep through the code leading up to the problem. Note that wild pointers can also be generated when Insure++ has only partial information about your program’s structure. For more information about this topic, contact Parasoft’s Quality Consultants.