如何在文件中打印一位而不是字节？

Question

我正在使用霍夫曼算法开发文件压缩器,现在我面临的问题是:

通过使用该算法:stackoverflow,我得到以下结果:

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%

所以我开始插入二进制树,这将得到结果:

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

这意味着树中角色的路径,考虑0为左,1为右.

然后单词"stackoverflow"将是:100110000100111010011111000010110110111011011111001010

好吧,我想将整个值放入一个二进制文件中,这将导致47位,这将是6字节,但我只能使它成为47字节,因为最小值将被放入一个文件与fwrite或者fprintf是1byte,使用sizeof(某事物).

比我的问题是:我如何只在我的文件中打印一下？

Answer 1

只需将"标题"写入文件:位数,然后将这些位"打包"为填充最后一位的字节.这是一个样本.

#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;
}

要做完整的霍夫曼编码器,你必须在开始时写入位代码.