Insure++ Reference - WRITE_NULL
This error is generated whenever an attempt is made to dereference a
NULL pointer.
This code attempts to use a pointer which has not been explicitly
assigned. Since the variable a is global, it is
initialized to zero by default, which results in dereferencing a
NULL pointer in line 8.
1: /*
2: * File: writnull.c
3: */
4: int *a;
5:
6: main()
7: {
8: *a = 123;
9: return (0);
10: }
[writnull.c:8] **WRITE_NULL**
1. >> *a = 123;
2. Writing null pointer: a
Stack trace where the error occurred:
3. main() writnull.c, 8
4. **Memory corrupted. Program may crash!!**
- Source line at which the problem was detected.
- Description of the problem and the expression that is in error.
- Stack trace showing the function call sequence leading to the
error.
- Informational message indicating that a serious error has
occurred which may cause the program to crash.
A common cause of this problem is the one shown in the example - use
of a pointer that has not been explicitly assigned and which is
initialized to zero. This is usually due to the omission of an assignment
or allocation statement which would give the pointer a reasonable value.
The example code might, for example, be corrected as follows
1: /*
2: * File: writnull.c (Modified)
3: */
4: int *a;
5:
6: main()
7: {
8: int b;
9:
10: a = &b;
11: *a = 123;
12: return (0);
13: }
A second common source of this error is code which dynamically
allocates memory but then zeroes pointers as blocks are freed. In this
case, the error would indicate reuse of a freed block.
A final common problem is caused when one of the dynamic memory
allocation routines, malloc, calloc , or
realloc , fails and returns a NULL
pointer. This can happen either because your program passes bad arguments
or simply because it asks for too much memory. A simple way of finding
this problem with Insure++ is to enable the
RETURN_FAILURE error code
via your .psrc file and run the program again. It
will then issue diagnostic messages every time a system call fails,
including the memory allocation routines.
WRITE_DANGLING
WRITE_OVERFLOW
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