With the introduction of void * pointers in the ANSI/ISO C Standard, explicitly casting the result of a call to malloc is no longer necessary and may even produce unexpected behavior if <stdlib.h> is not included.

Non-Compliant Code Example

If stdlib.h is not included, the compiler makes the assumption that malloc() has a return type of int. When the result of a call to malloc() is explicitly cast to a pointer type, the compiler assumes that the cast from int to a pointer type is done with full knowledge of the possible outcomes. This may lead to behavior that is unexpected by the programmer.

char *p = (char *)malloc(10);

Compliant Solution

By omitting the explicit cast to a pointer, the compiler can determine that an int is attempting to be assigned to a pointer type and will generate a warning that may easily be corrected.

#include <stdlib.h>
/* ... */
char *p = malloc(10);

Exceptions

The return value from malloc() may be cast in C code that needs to be compatible with C++, where explicit casts from void * are required.

Risk Assessment

Explicitly casting the return value of malloc() eliminates the warning for the implicit declaration of malloc().

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

References

\[[Summit 05|AA. C References#Summit 05]\] [Question 7.7|http://c-faq.com/malloc/cast.html], [Question 7.7b|http://c-faq.com/malloc/mallocnocast.html]

MEM01-A. Eliminate dangling pointers      08. Memory Management (MEM)       MEM03-A. Clear sensitive information stored in dynamic memory prior to deallocation