Page History

...

C99 and C90 allow a pointer to be cast into and out of void *. As a result, it is possible to silently convert from one pointer type to another without the compiler diagnosing the problem by storing or casting a pointer to void * and then storing or casting it to the final type. In this noncompliant code example, the type checking system is circumvented due to the caveats of void pointers.

char *loop_ptr;
int *int_ptr;

int *loop_function(void *v_pointer) {
  /* ... */
  return v_pointer;
}
int_ptr = loop_function(loop_ptr);

...

Because the input parameter directly influences the return value, and loop_function() returns an int *, the formal parameter v_pointer is redeclared to only accept int *.

int *loop_ptr;
int *int_ptr;

int *loop_function(int *v_pointer) {
  /* ... */
  return v_pointer;
}
int_ptr = loop_function(loop_ptr);

...

Many architectures require that pointers are correctly aligned when accessing objects bigger than a byte. There are, however, many places in system code where you receive unaligned data (for example, the network stacks) that needs to be copied to a properly aligned memory location, such as in this noncompliant code example.

char *data;
struct foo_header *tmp;
struct foo_header *header;

tmp = data + offset;
memcpy(&header, tmp, sizeof(header));

if (header.len < FOO)
/* ... */

...

This compliant solution does not use the foo_header pointer.

char *data;
struct foo_header header;

memcpy(&header, data + offset, sizeof(header));

if (header.len < FOO)
/* ... */

...