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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 #include <stdlib.h> is forgottennot 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 then explicitly cast to a pointer type, the compiler will assume assumes that the cast from int to a pointer type is done with full knowledge of the possible outcomes. This may lead to behavior which is unexpected by the programmer.

...

Code Block
#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.

References

comp.lang.c FAQ list - Question 7.7 http://c-faq.com/malloc/cast.html
comp.lang.c FAQ list - Question 7.7b http://c-faq.com/malloc/mallocnocast.html