Question

I’m not sure the proper way to handle the casting of types when using malloc. I’m coming from Objective C where the following is perfectly legal:

ALuint * sources;
sources=malloc(sizeof(ALuint)*32);

However, in C++ the compiler says “Assigning to ALuint * from incompatible type void *”.

I get that the memory returned from malloc is not casted as my particular type, and I get that C++ is strict with types.

Now, I could do this:

 sources=(ALuint*)malloc(sizeof(ALuint)*32);

But I have read much wiser coders than myself say never to cast in such a manner. Why not? And if not, when or how is the best time or method to make this work?

Answer 1

1. Avoid using malloc in C++.
2. If you must #1, You must cast the return type of malloc for your code to compile.
3. Only exception to #2 is if your target pointer is a void pointer.
4. Not casting the return of malloc is (debatebly)considered as good practice in C.

So, In C++ a cast is necessary. The type of cast to use is also important though. It should definitely not be the c-style cast. The above links were demonstration of need of cast only.

---

Now, I could do this:

sources=(ALuint*)malloc(sizeof(ALuint)*32);

But I have read much wiser coders than myself say never to cast in such a manner. Why not?

---

Because in C++ a c-style cast is defined by the standard to map to C++ cast in following order. The first one to succeed will be used:

1. const_cast
2. static_cast
3. static_cast, then const_cast
4. reinterpret_cast
5. reinterpret_cast, then const_cast

As you see a c-styled cast might in fact result in reinterpret_cast which is potentially dangerous as it can cast between incompatible pointer types. So if you must use malloc use:

sources=static_cast<ALuint*>malloc(sizeof(ALuint)*32);