写位在C文件 [英] Writing bits to a file in C

问题描述

我有这样的字符串：101
我想将其写入文件，在C，而不是文字：101等8位×字符。但直接使用字符串作为位：位1，比特0和比特1，这样该文件将成为3位

I have this string: "101" I want to write it to a file, in C, not as text: "101" and so 8 bits x char. but directly use the string as bits: the bit "1", the bit "0" and the bit "1", so that the file will be of 3 bits.

难道不可能性？
我搜索在网络上，我试着这样做：

Is it possibile? I searched on the web and I tried doing this:

char c[25] = "101";
FILE *binFile = fopen("binFile.bin", "wb");
int x = atoi(c);
fwrite(&x, sizeof(x), 1, binFile);

但在最后，当我确认文件的字节时，Windows说我，这是4字节的文件！而不是3比特！

But at the end, when I verify files's bytes, Windows says me that it is 4bytes file! And not 3bits!

我怎么能做到这一点，如果可能的话？非常感谢。

How can I do this, if it is possible? Thanks a lot.

推荐答案

所有filesystems¹处理文件中的字节术语（和一个更大的粒度分配存储空间，在一个时间最小512字节）。有没有办法，你会得到一个文件，是的 3位的长。

All filesystems¹ deal with files in terms of bytes (and allocate storage space with a much larger granularity, 512 bytes at a time minimum). There's no way you are going to get a file that is 3 bits long.

你能做的最好的是使用了一整字节，但忽略其位5。要做到这一点（假设数总是要适应一个字节），输入字符串转换为整数类型：

The best you can do is use up one whole byte but ignore 5 of its bits. To do that (assuming that the number is always going to fit into a byte), convert the input string to an integral type:

long l = strtol(c, 0, 2);

然后得到其最显著字节：

Then get its least significant byte:

unsigned char b = l & 0xffl;

并将其写入文件：

And write it to the file:

fwrite(&b, 1, 1, binFile);

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¹好吧，也许不是全部。可能有一些研究人员的地方，实验位大小的文件系统。我不知道。

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¹ Well, maybe not all. There might be some researchers somewhere that experiment with bit-sized filesystems. I wouldn't know.

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