Branching Around Code

The following example contains a logic error where the program dereferences a null pointer:

1 int check_for_error (int *error_ptr)

2 {

3 *error_ptr = global_error;

4 global_error = 0;

5 return (global_error != 0);

6 }

The error occurs because the routine that calls this function assumes that the value of error_ptr can be 0. The check_for_error() function, however, assumes that error_ptr isn’t null, which means that line 3 can dereference a null pointer.

You can correct this error by setting an eval point on line 3 and entering:

if (error_ptr == 0) goto 4;

If the value of error_ptr is null, line 3 isn’t executed. Note that you are not naming a label used in your program. Instead, you are naming one of the line numbers generated by TotalView.