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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 which that is unexpected by the programmer.
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By ommiting 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 which that may easily be corrected.
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#include <stdlib.h> ... char *p = malloc(10); |
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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