Is the type cast necessary when using malloc in C?

I am learning how to use malloc, and I am seeing that most people think it's necessary to make a type cast when passing the memory address to the pointer. For example, here's a code to get 16 new bytes allocated (4 ints) using malloc:

Code:

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#include <stdlib.h>

int main(){
  int *p;
  p = (int *)malloc(4*sizeof(int));

  return 0;
}

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My question: is the (int *) cast on the right side of the attribution necessary? After all p is already a pointer to ints, so the pointer arithmetic should work fine even without that cast.

Thanks

One word answer: No.

Cprogramming.com FAQ > Casting malloc

Tim S.

Thanks. I suspected, but better to cross check with the pros.

Quote:

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Originally Posted by envec83

My question: is the (int *) cast on the right side of the attribution necessary? After all p is already a pointer to ints, so the pointer arithmetic should work fine even without that cast.

Thanks

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More specifically: There is no pointer arithmetic going on here, so any worry about that is worrisome (at least on our part, because it makes us worry you have no idea what's going on). The point of the cast is that the right side and the left side are of different types -- p is an int*, as you say; and malloc returns a void*. In C, no cast is needed (or desired) to convert from void* to int*, so we suggest that you don't put it in. (And naturally, you cannot change the type of p just by assigning something to it, so it's not as though p magically becomes a void* even though it was declared as a int*.)

Microsoft's C++ compiler which I use to compile C programs (extension .cpp) whines if I do not cast. So I do. But people get yelled at here for putting it in...
Presumably because if one forgets to include the necessary prototype for malloc, any explicit cast would mask a serious error because malloc would be forced to return an int type as per default when no type is specified.
I don't forget my includes and I still I like to cast because I like to get zero errors and zero warnings at the highest warning level.

Wouldn't it be easier to just use the .c extension? (ETA: Although there are probably other fiddly things that would break then. I don't use VS enough to know.)

Quote:

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Originally Posted by nonoob

Microsoft's C++ compiler which I use to compile C programs (extension .cpp) whines if I do not cast.

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That's because you are compiling as C++ and not C. C doesn't need a cast, C++ does.


Quzah.

No, it's because VS is stupid. The error highlighting highlights C++ errors only. I have a test project, with only .c files, and the project type is explicitly set to C, and those errors are still highlighted. The only option I'm aware of is to disable the error highlighting all together: Tools->Options->Text Editor->C/C++->Advanced->Disable Error Reporting or Disable Squiggles (the former turning off all background parsing, the latter just the display).

Quote:

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Originally Posted by anduril462

No, it's because VS is stupid. The error highlighting highlights C++ errors only. I have a test project, with only .c files, and the project type is explicitly set to C, and those errors are still highlighted.

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I take the emphasized part to mean that you have set the project to be compiled as C, yes?

Quote:

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Originally Posted by nonoob

Microsoft's C++ compiler which I use to compile C programs (extension .cpp) whines if I do not cast. So I do. But people get yelled at here for putting it in...
Presumably because if one forgets to include the necessary prototype for malloc, any explicit cast would mask a serious error because malloc would be forced to return an int type as per default when no type is specified.
I don't forget my includes and I still I like to cast because I like to get zero errors and zero warnings at the highest warning level.

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Use the .c extension and specify the -Tc compiler option. Otherwise you're building C++ programs...

I myself try to stay away from VS for any pure C work. It sort of feels like using an aircraft to mow my lawn.

Quote:

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Originally Posted by msh

I take the emphasized part to mean that you have set the project to be compiled as C, yes?

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Yes, that is what I meant.