在 C 中使用位域的正确方法是什么？

发布于 2024-07-14 08:17:15 字数 501 浏览 6 评论 0原文

我正在使用位字段来轻松访问我正在尝试为没有 FPU 的微控制器制作的浮点库。

问题是我似乎无法使其与位字段一起使用。看一下：

typedef struct
{
   union{
    unsigned long mantissa: 23;
    unsigned long exponent: 8;
    unsigned long sign: 1;
    float all;

      };

}_float __attribute__((__packed__));

问题是，当我尝试访问或更改任何内容时，它会将位域分别视为距末尾 1、8、23 位。虽然它应该是从末尾开始 23 位，然后是 8 位，然后是最后一位。除非我完全误解了位域的使用。我认为使用 packed 可以解决问题，但正如你所看到的，它没有解决。

任何帮助将非常感激。我不止一次在谷歌搜索时被引导到这个网站，所以我抱有很高的期望。

原文

I am using bitfields to get easy access on a float library I am trying to make for a microcontroller with no FPU.

The problem is that I can't seem to make it work with bitfields. Take a look:

typedef struct
{
   union{
    unsigned long mantissa: 23;
    unsigned long exponent: 8;
    unsigned long sign: 1;
    float all;

      };

}_float __attribute__((__packed__));

The problem is that when I try to access or change anything it considers the bitfields as 1,8,23 bits from the end respectively. While it should be 23 bits from the end, then 8 bits and then the last bit. Unless I have totally misunderstood the use of bitfields. I thought that using packed would solve the problem but as you can see it didn't.

Any help would be really appreciated. I have been lead to this site while googling more than once so I have high hopes.

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触ぅ动初心 2024-07-21 08:17:15

您可能缺少联合内的结构。

typedef struct
{
    union{
       struct {
           unsigned long mantissa: 23;
           unsigned long exponent: 8;
           unsigned long sign: 1;
       } float_parts;
       float all;
    };
}_float __attribute__((__packed__));

请注意，尾数/指数和符号的顺序取决于 cpu 的字节顺序。

You might be missing a struct inside your union.

typedef struct
{
    union{
       struct {
           unsigned long mantissa: 23;
           unsigned long exponent: 8;
           unsigned long sign: 1;
       } float_parts;
       float all;
    };
}_float __attribute__((__packed__));

Note that the order of mantissa/exponent and sign depends one the endianess of the cpu.

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