指针数组和sizeof混淆

2021-12-13 00:00:00 pointers c++

为什么下面的代码输出4?

Why does the following code output 4?

char** pointer = new char*[1]; std::cout << sizeof(pointer) << " ";

我有一个指针数组，但它的长度应该是 1，不是吗?

I have an array of pointers, but it should have length 1, shouldn't it?

推荐答案

pointer 是一个指针.它是指针的大小，在您的系统上为 4 个字节.

pointer is a pointer. It is the size of a pointer, which is 4 bytes on your system.

*pointer 也是一个指针.sizeof(*pointer) 也将是 4.

*pointer is also a pointer. sizeof(*pointer) will also be 4.

**pointer 是一个字符.sizeof(**pointer) 将是 1.注意 **pointer 是一个字符，因为它被定义为 char**.new`ed 数组的大小永远不会进入这个.

**pointer is a char. sizeof(**pointer) will be 1. Note that **pointer is a char because it is defined as char**. The size of the array new`ed nevers enters into this.

注意 sizeof 是一个编译器操作符.它在编译时呈现为常量.任何可以在运行时更改的内容(例如新数组的大小)都无法使用 sizeof 来确定.

Note that sizeof is a compiler operator. It is rendered to a constant at compile time. Anything that could be changed at runtime (like the size of a new'ed array) cannnot be determined using sizeof.

注 2:如果您已将其定义为:

Note 2: If you had defined that as:

char* array[1]; char** pointer = array;

现在 pointer 的值与以前基本相同，但现在您可以说:

Now pointer has essencially the same value as before, but now you can say:

int arraySize = sizeof(array); // size of total space of array int arrayLen = sizeof(array)/sizeof(array[0]); // number of element == 1 here.

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