如何在文件中打印一个位而不是字节？ [英] How can I print a bit instead of byte in a file?

问题描述

我使用huffman算法开发一个文件压缩器，现在我面临的问题是：

通过使用算法到字：
stackoverflow，我得到以下结果：

  a，c，e，f，k，l，r，s，t ，v，w = 1次重复
o = 2次重复
 
a，c，e，f，k，l，r，s，t，v，w = 7.69231％
和
o = 15.3846％
  

所以我开始插入二叉树给我的结果：

  o = 00 
a = 010 
e = 0110 
c = 0111 
t = 1000 
s = 1001 
w = 1010 
v = 1011 
k = 1100 
f = 1101 
r = 1110 
l = 1111 
  

这意味着树中字符的路径，考虑0为左和1到右。 p>

那么单词stackoverflow将是：
100110000100111010011111000010110110111011011111001010

整数值变成一个二进制文件，以位为单位，这将导致47位，这将发生6个字节，但相反我只能使它47bytes，因为使用fwrite或fprintf放入一个文件的最小是1字节，通过使用sizeof （$）

比我的问题是：我怎么才能在我的文件中打印一个位？

解决方案

只需将头写入文件：位数，然后填充位到字节填充最后一个。这是一个示例。

  #include< stdio.h> 
 
 FILE * f; 
 
 / *当前字节多少位* / 
 int bit_counter; 
 / *当前字节* / 
 unsigned char cur_byte; 
 
 / *写1或0位* / 
 void write_bit（unsigned char bit）
 {
 if（++ bit_counter == 8）
 {
 fwrite（& cur_byte，1,1，f）; 
 bit_counter = 0; 
 cur_byte = 0; 
} 
 
 cur_byte<< = 1; 
 cur_byte | = bit; 
} 
 
 int main（）
 {
 f = fopen（test.bits，w）; 
 
 cur_byte = 0; 
 bit_counter = 0; 
 
 / *写这里的位数来解码比特流（在你的情况下为47）* / 
 / * int num = 47; * / 
 / * fwrite（num，1,4，f）; * / 
 
 write_bit（1）; 
 write_bit（0）; 
 write_bit（0）; 
 / * etc ...  - 在每个编码字符的循环中这样做* / 
 / * 100110000100111010011111000010110110111011011111001010 * / 
 
 if（bit_counter> 0）
 {
 //用零替换最后一个字节
 cur_byte <= 8  -  bit_counter; 
 fwrite（& cur_byte，1,1，f）; 
} 
 
 fclose（f）; 
 
 return 0; 
} 
  

要做完整的霍夫曼编码器，你必须写位码当然是开始。

I am using huffman algorithm to develop a file compressor and right now I am facing a problem which is:

By using the algorithm to the word: stackoverflow, i get the following result:

a,c,e,f,k,l,r,s,t,v,w = 1 time repeated
o = 2 times repeated

a,c,e,f,k,l,r,s,t,v,w = 7.69231%
and
o = 15.3846%

So I start inserting then into a Binary Tree, which will get me the results:

o=00
a=010
e=0110
c=0111
t=1000
s=1001
w=1010
v=1011
k=1100
f=1101
r=1110
l=1111

which means the path for the character in the tree, considering 0 to be left and 1 to right.

then the word "stackoverflow" will be: 100110000100111010011111000010110110111011011111001010

and well, I want to put that whole value into a binary file to be in bits, which will result in 47bits, which would happen to be 6bytes, but instead I can only make it 47bytes because the minimun to put into a file with fwrite or fprintf is 1byte, by using sizeof(something).

Than my question is: how can I print in my file only a single bit?

解决方案

Just write the "header" to the file: the number of bits and then "pack" the bits into bytes padding the last one. Here's a sample.

#include <stdio.h>

FILE* f;

/* how many bits in current byte */
int bit_counter;
/* current byte */
unsigned char cur_byte;

/* write 1 or 0 bit */
void write_bit(unsigned char bit)
{
    if(++bit_counter == 8)
    {
        fwrite(&cur_byte,1,1,f);
        bit_counter = 0;
        cur_byte = 0;
    }

    cur_byte <<= 1;
    cur_byte |= bit;
}

int main()
{
    f = fopen("test.bits", "w");

    cur_byte = 0;
    bit_counter = 0;

    /* write the number of bits here to decode the bitstream later (47 in your case) */
    /* int num = 47; */           
    /* fwrite(num, 1, 4, f); */

    write_bit(1);
    write_bit(0);
    write_bit(0);
    /* etc...  - do this in a loop for each encoded character */
    /* 100110000100111010011111000010110110111011011111001010 */

    if(bit_counter > 0)
    {
         // pad the last byte with zeroes
         cur_byte <<= 8 - bit_counter;
         fwrite(&cur_byte, 1, 1, f);
    }

    fclose(f);

    return 0;
}

To do the full Huffman encoder you'll have to write the bit codes at the beginning, of course.

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