【C++】cstddef中4个定义

最新推荐文章于 2025-02-25 20:02:37 发布

原创最新推荐文章于 2025-02-25 20:02:37 发布 · 4k 阅读

5 ·

CC 4.0 BY-SA版权

文章标签：

#c++ #null #structure #file #c

C/C++/STL 专栏收录该内容

6 篇文章

订阅专栏

本文介绍了C++标准库头文件<cstddef>中四个重要的类型定义：size_t用于表示sizeof操作的结果，是无符号整型；NULL是空指针常量，在C++中通常为0；ptrdiff_t是两个指针相减得到的差值的类型；offsetof宏用于获取结构体中成员相对于结构体起始位置的字节数偏移。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

size_t

size_t corresponds to the integral data type returned by the language operator sizeof and is defined in the <cstddef> header file (among others) as an unsigned integral type.
size_t = unsigned int

NULL

This macro expands to a null pointer constant.

A null pointer is generally used to signify that a pointer does not point to any object.
In C++, NULL expands either to 0 or 0L.

在c中null经常被定义为(void)*0，即为空指针，而在C++中null为一整型0。

ptrdiff_t

This is the type returned by the subtraction operation between two pointers.

两个指针相减之差。

offsetof

offsetof (type,member)

This macro with functional form returns the offset value in bytes of member member in the structure type type.

此函数形式的宏返回member在结构type中的偏移。

/* offsetof example */
#include <stdio.h>
#include <stddef.h>

struct mystruct {
    char singlechar;
    char arraymember[10];
    char anotherchar;
};

int main ()
{
    printf ("offsetof(mystruct,singlechar) is %d\n",offsetof(mystruct,singlechar));
    printf ("offsetof(mystruct,arraymember) is %d\n",offsetof(mystruct,arraymember));
    printf ("offsetof(mystruct,anotherchar) is %d\n",offsetof(mystruct,anotherchar));
  
    return 0;
}