结构大小与 typedef 版本不同? [英] struct size is different from typedef version?

问题描述

我的代码中有以下结构声明和 typedef:

I have the following struct declaration and typedef in my code:

struct blockHeaderStruct {
    bool allocated;
    unsigned int length;
};
typedef struct blockHeaderStruct blockHeader;

当我做 sizeof(blockheader) 时，我得到了 4 个字节的值，但是当我做 sizeof(struct blockHeaderStruct) 时，我得到了 8 个字节.

When I do sizeof(blockheader), I get the value of 4 bytes back, but when I do sizeof(struct blockHeaderStruct), I get 8 bytes.

为什么会这样?为什么我不拿回 5?

Why is this happening? Why am I not getting 5 back instead?

推荐答案

查看结构的定义，您有 1 个字节的值，后跟 4 个字节的整数.这个整数需要在 4 字节边界上分配，这将强制编译器在 1 字节 bool 之后插入 3 字节填充.这使得 struct 的大小为 8 字节.为了避免这种情况，您可以更改结构中元素的顺序.

Looking at the definition of your struct, you have 1 byte value followed by 4 byte Integer. This integer needs to be allocated on 4 byte boundary, which will force compiler to insert a 3 byte padding after your 1 byte bool. Which makes the size of struct to 8 byte. To avoid this you can change order of elements in the struct.

另外，对于返回不同值的两个 sizeof 调用，您确定这里没有打字错误，并且您没有获取指针或不同类型或某些整数变量的大小.

Also for two sizeof calls returning different values, are you sure you do not have a typo here and you are not taking size of pointer or different type or some integer variable.

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