Dangling Pointers

If you enable memory debugging, TotalView displays information in the Variable Window about the variable’s memory status; that is, whether the memory is allocated or deallocated. The following small program allocates a memory block, sets a pointer to the middle of the block, and then deallocates the block:

main(int argc, char **argv)

{

int *addr = 0; /* Pointer to start of block. */

int *misaddr = 0; /* Pointer to interior of block. */

addr = (int *) malloc (10 * sizeof(int));

misaddr = addr + 5; /* Point to block interior */

/* Deallocate the block. addr and */

/* misaddr are now dangling. */

free (addr);

}

Figure 25 shows two Variable Windows. Execution was stopped before your program executed the free() function. Both windows contain a memory indicator saying that blocks are allocated.

 

Figure 25: Allocated Descriptions in a Variable Window

After your program executes the free() function, the messages change, Figure 26.

 

Figure 26: Dangling Description in a Variable Window