使用unsigned long long int进行动态分配

Question

If I have the following variable unsigned long long int *size , is it a good practice to leave size = calloc(2, sizeof(int)) or it should be size = calloc(2, sizeof(unsigned long long int)) ?

Thank you

Answer 1

Second option. You don't want to make assumptions about datatype sizes in c.
It is very platform/compiler dependent.

Answer 2

There is no reason to assume that int and unsigned long long int are the same size (they may be). If size is declared as unsigned long long int , then of the two options presented, the correct choice is:

size = calloc(2, sizeof(unsigned long long int));

A better practice is to avoid using explicit types with sizeof :

size = calloc(2, sizeof *size);

This is less error-prone in the initial coding, and more maintainable. If types change during the lifetime of the code, only the declaration needs to be changed here.

Answer 3

The size of int can be either 2 or 4 bytes, depending on the machine you run.
However, the size of unsigned long long is at least 8 bytes.

So no, it is NOT a good practice to use a worng size.