将原始二进制文件写入C中的文件

Question

I am trying to write raw binary bits at a time to a file.

I have found an example that uses unsigned char -> https://stackoverflow.com/a/2666669/1541965

But the minimum size is 8 bit (because of the unsigned char 0 to 255).

Is there a way to write bits to a file in a more direct way?

Thanks.

Answer 1

You haven't said what operating system you're using. But generally the smallest unit you get to write to a file is one 8-bit byte. If you want to write individual bits, you'll need to assemble them into bytes in your own code. I don't know of any OS whose file IO facilities allow writing of individual bits.

Answer 2

No, there isn't, at least not directly. C's I/O model for binary files is that they're sequences of bytes (typically 8 bits).

What you can do is, in your own code, write a function that takes a 1-bit value and gathers the bits into a byte, writing them to the file when it's received 8 bits. You'll also need to do an additional write at the end if the byte value hasn't been filed yet.

It's not possible to write a partial byte; you can, if necessary, pad the last byte with zeros if necessary.

(The C standard requires a byte to be at least 8 bits, but it permits it to be more. The number of bits in a byte is specified by CHAR_BIT , defined in <limits.h> . CHAR_BIT is going to be exactly 8 on any system you're likely to encounter.)

Answer 3

Computer architecture does not allow you to split the byte, which is 8 bits. PCs work on 8 bits. Turing's Colossus worked on 5 bits (because in Baudot's code the number 2^5 is enough ).

The microprocessors do not have instructions to deal with units less than a byte (even bits operations like or, use on 1,2,4,8 bits).