1. size_t cstddef types are defined in the header file, the file is a header file of the C standard library stddef.h the C ++ version. It is an unsigned type associated with the machine, which is large enough to ensure that the size of objects stored in memory.
2. calloc function: memory, dynamic memory allocation area n independent continuous space size, the starting address of the function returns a pointer to the allocated pointer ; if the allocation is not successful, returns NULL. And malloc difference:
After completion calloc dynamic memory allocation, memory is automatically initialized to zero, but does not initialize malloc, inside the garbage data is random data.
3.