使用 stdio 加载数据时处理不同的架构

发布于 2024-11-19 11:29:23 字数 364 浏览 2 评论 0原文

我想从文件中读入一些数据。说一个整数：

fread(&var1, 4, 1, f);

其中 var1 是一个整数。但后来我开始认为这不安全，因为不能保证整数的长度是 4 个字节。（为了这个问题，我忽略了其他问题，例如 feof 和ferror）。

我也很快意识到，除了 int 大小之外，还有更多问题，例如系统的字节顺序，以及可能还有其他我没有想到的问题。

那么，确保正确解释正在读入的数据的最佳方法是什么？到目前为止，我唯一能想到的就是将数据存储为文本而不是二进制数据，读取文本，并在运行时转换它。我猜想，无论解决方案如何，如果您想确保它是可移植的，它总是会涉及某种形式的转换。

谢谢。

原文

I want to read in some data from a file. Say an integer:

fread(&var1, 4, 1, f);

Where var1 would be an integer. But then I got to thinking that this is not safe as there isn't any guarantee that an integer is 4 bytes long. (I'm ignoring other issues like feof and ferror for the sake of this question).

I also soon realised that there were even more issues than just int size, such as the endianness of the system, and probably others which I haven't even thought of.

So, what is the best way to ensure that you data being read in is interpreted properly? So far, the only thing I can think of is to just store the data as text rather than as binary data, read in the text, and convert it at run time. I would guess that no matter the solution though, if you wanted to ensure that it is portable, it would always involve some form of conversion anyway.

Thank you.

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陪我终i 2024-11-26 11:29:23

为了避免大小问题，您应该这样做：

fread(&var1, sizeof(var1), 1, f);

如果您担心 int 的大小可能在写入数据的平台和读取数据的平台之间有所不同，那么您有更多根本问题。在这种情况下，应该避免使用 int、short 等，而使用中定义的类型，例如如int16_t、uint32_t。

要处理字节顺序问题，您应该考虑编写辅助函数，以已知的顺序显式写入/读取各个字节，例如：

void write_uint32_t(uint8_t *buf, uint32_t x)
{
    buf[0] = (uint8_t)(x >> 0);
    buf[1] = (uint8_t)(x >> 8);
    buf[2] = (uint8_t)(x >> 16);
    buf[3] = (uint8_t)(x >> 24);
}

上述所有内容仅适用于整数类型。对于浮点类型，没有完美的通用解决方案。

To avoid the size problem, you should be doing:

fread(&var1, sizeof(var1), 1, f);

If you're worried that the size of int might vary between the platform that writes the data and the platform that reads the data, then you have a more fundamental problem. In this scenario, you should avoid using int, short, etc., and use the types defined in <stdint.h>, such as int16_t, uint32_t.

To deal with endianness issues, you should consider writing helper functions that explicitly write/read the individual bytes in a known order, such as:

void write_uint32_t(uint8_t *buf, uint32_t x)
{
    buf[0] = (uint8_t)(x >> 0);
    buf[1] = (uint8_t)(x >> 8);
    buf[2] = (uint8_t)(x >> 16);
    buf[3] = (uint8_t)(x >> 24);
}

All of the above applies only to integer types. For floating-point types, there is no perfect universal solution.

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