不sizeof操作符需要用C哪些参数？ [英] What arguments does the sizeof operator take in C?

问题描述

[原标题提到sizeof的功能。的]

我尝试了这些，他们都工作：

I tried these and they all worked:

char *p;

printf("Size of *p is %d\n",sizeof(*p));  //result =1
printf("Size of  p is %d\n",sizeof( p));  //result =4
printf("Size of  p is %d\n",sizeof(&p));  //result =4

我不知道为什么第一个printf是1，第2和第3是4？
所以可以sizeof的实际上可以采取什么样的参数？

I wonder why the first printf is 1, the 2nd and 3rd is 4? So what arguments can sizeof can actually take?

推荐答案

这需要一个类型。

的sizeof（char）的始终为1。变量 P 本身就是一个指针，你的平台上，有一个大小4.然后你做＆安培; P 或一个指针的指针，其中也有一个尺寸为4

sizeof(char) is always one. The variable p itself is a pointer, and on your platform that has a size of 4. Then you do &p, or a pointer to a pointer, which also has a size of 4.

在大多数现代桌面系统，32位架构将有4个字节的指针，而64位架构将有8个字节的指针。

On most modern desktop systems, a 32-bit architecture will have 4 byte pointers, while a 64-bit architecture will have 8 byte pointers.

的sizeof 本身是一个关键字，在编译时解决，而不是一个函数。在C99，数组可以是可变长度，和sizeof会等到运行时来解决这个尺寸。

sizeof itself is a keyword, resolved at compile-time, not a function. In C99, arrays can be variable length, and sizeof will wait until run-time to resolve this size.

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