Question

What does this statement mean?

//allocated memory for Device info

(*PppsCoreStructure)->psDeviceDetails=(sDeviceDetails **)calloc(CORE_DEVICEINFO_SIZE, sizeof(sDeviceDetails*));

I know that ‘(*PppsCoreStructure)->psDeviceDetails’ is a pointer to pointer. But I am not being able to imagine how calloc can return pointer to pointer? I’m a beginner please help

Answer 1

• (*PppsCoreStructure)->psDeviceDetails is declared with type sDeviceDetails **
• The return value of calloc() is of type void*
• (sDeviceDetails **)calloc(...) casts the return value of calloc to be of type sDeviceDetails **

In the C++ language this type cast is essential, although in C++ one would normally not be using calloc and would probably be using C++ casts.

In the C language the type cast is not needed because a void* pointer is assignment compatible with all other pointer types.

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In a comment you state

But I want know how sDeviceDetails* is different from sDeviceDetails**

and I suspect that this is in fact your real question.

The answer is simple enough: T* is a pointer-to-T and T** is a pointer-to-pointer-to-T.