size_t and ptrdiff_t

主要参考文章:

1、pvs-studio About size_t and ptrdiff_t

总结如下

一、

unsigned	size_t	uintptr_t
signed	ptrdiff_t	intptr_t

1、cppreference ptrdiff_t

ptrdiff_t acts as the signed counterpart of size_t: it can store the size of the array of any type and is, on most platforms, synonymous with intptr_t).

二、

它们都和pointer有着密切关联:

size_t length等于pointer length

ptrdiff_t length等于pointer length

在 pvs-studio About size_t and ptrdiff_t # "Portability of size_t and ptrdiff_t"段中，有着这样对待总结:

The size of size_t and ptrdiff_t always coincide with the pointer's size. Because of this, it is these types which should be used as indexes for large arrays, for storage of pointers and, pointer arithmetic.

三、ptrdiff_t 和 size_t 都是与机器相关的数据类型，因此它们都是implementation defined。

四、使用它们能够实现:

1、Portability

2、Safety of ptrdiff_t and size_t types in address arithmetic

3、Performance of code using ptrdiff_t and size_t

省去了data conversion command

stackoverflow C++ size_t or ptrdiff_t

对比int

int是fixed length的，是机器不相关的；