Michi Michi - 1 month ago 11
C Question

Why does the Book say I must cast malloc?

Today I reached page 167 of The C Programming Language (second edition Brian W. Kernighan & Dennis M. Ritchie) and found that the author says I must cast

malloc
. Here is the part from the book:


7.8.5 Storage Management

The functions malloc and calloc obtain blocks of memory dynamically.

void *malloc(size_t n)


returns a pointer to n bytes of uninitialized storage, or NULL if the request cannot be satisfied.

void *calloc(size_t n, size_t size)


returns a pointer to enough free space for an array of n objects of the specified size, or NULL if
the request cannot be satisfied. The storage is initialized to zero.
The pointer returned by malloc or calloc has the proper alignment for the object in question,
but it must be cast into the appropriate type, as in

int *ip;
ip = (int *) calloc(n, sizeof(int));



I already know that
malloc
(and its family) returns type void*, and there are good explanations why not to cast
malloc
.

But my question is: Why does the book say I should cast it?

Answer

From http://computer-programming-forum.com/47-c-language/a9c4a586c7dcd3fe.htm:

In pre-ANSI C -- as described in K&R-1 -- malloc() returned a char * and it was necessary to cast its return value in all cases where the receiving variable was not also a char *. The new void * type in Standard C makes these contortions unnecessary.

To save anybody from the embarrassment of leaping needlessly to the defence of K&R-2, I asked Dennis Ritchie for an opinion that I could quote on the validity of the sentence cited above from page 142. He replied:

In any case, now that I reread the stuff on p. 142, I think it's wrong; it's written in such a way that it's not just defensive against earlier rules, it misrepresents the ANSI rules.