C＋＋库研究笔记——几个注意（size_t)

总之，用size_t 保证可移植性，保证其可以表示出最大需要表示的长度。

size_t 在stddef.h 中无命名空间

在<cstddef>有std::

size_t 与ptrdiff_t 要联合使用

When

i

is
signed and

size

is
unsigned, then

i

is
converted to unsigned before the comparison is performed. This is part of what are called the usual arithmetic conversions.http://stackoverflow.com/questions/4311538/strange-behaviour-with-for-loop-and-size-t

unsigned int vs.
size_t:

When to use std::size_t?

Difference
between size_t and std::size_t

About size_t and ptrdiff_t

(ptrdiff_t 在64位下有更高的效率）

#include <iostream>
#include <stddef.h>

template <typename T, int N>
int size(T (&)
)
{
    return N;
}

int main()
{
    int a[20];
    std::cout<<size(a)<<std::endl;

    std::cout<<"sizeof(short):"<<sizeof(short)<<std::endl;
    std::cout<<"sizeof(float):"<<sizeof(float)<<std::endl;
    std::cout<<"sizeof(double):"<<sizeof(double)<<std::endl;
    std::cout<<"sizeof(long):"<<sizeof(long)<<std::endl;
    std::cout<<"sizeof(size_t):"<<sizeof(size_t)<<std::endl;

    std::cout<<"sizeof(ptrdiff_t):"<<sizeof(ptrdiff_t)<<std::endl;  // error when not using #include <stddef.h>
    std::cout<<"sizeof(ptrdiff_t):"<<sizeof(std::ptrdiff_t)<<std::endl;
    return 0;
}

结果：

20

sizeof(short):2

sizeof(float):4

sizeof(double):8

sizeof(long):8

sizeof(size_t):8

sizeof(ptrdiff_t):8

sizeof(ptrdiff_t):8