sizeof(struct) 返回意外值

2021-12-23 00:00:00 gcc struct mingw c++ sizeof

这应该很简单，但我不知道去哪里寻找问题:

This should be simple but I have no clue where to look for the issue:

我有一个结构:

struct region
{
public:
    long long int x;
    long long int y;
    long long int width;
    long long int height;
    unsigned char scale;
};

当我做 sizeof(region) 时，它给了我 40 当我期待 33 时.

When I do sizeof(region) it gives me 40 when I am expecting 33.

有什么想法吗?

(mingw gcc，赢得 x64 操作系统)

(mingw gcc, win x64 os)

推荐答案

它正在填充结构以适应 8 字节的边界.所以它实际上在内存中占用了 40 个字节 - sizeof 返回了正确的值.

It's padding the struct to fit an 8-byte boundary. So it actually is taking 40 bytes in memory - sizeof is returning the correct value.

如果您希望它只占用 33 个字节，则指定 packed 属性:

If you want it to only take 33 bytes then specify the packed attribute:

struct region
{
public:
    long long int x;
    long long int y;
    long long int width;
    long long int height;
    unsigned char scale;
} __attribute__ ((packed));

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