Compressing file using a binary file

bernie82 · 05-31-2005, 10:40 PM

Hi there, At the moment I am trying to create a file that contains just the characters '0' and '1'. I am trying to compress a text file by using my own coding scheme but I can't write to a file using C that actually compresses because it takes one byte to represent '0' or '1'. Can this be done through C? PLEASE HELP! THANKS!

trutnev · 05-31-2005, 11:04 PM

do you want to work with bits with bitwise operators ?

bernie82 · 06-01-2005, 01:19 AM

Basically, i have a string like this for example:
001110100
And I want to write this to some file but not have it encoded as a text file.
I need this saved as a binary file.

itsme86 · 06-01-2005, 02:11 AM

Code:

itsme@itsme:~/C$ cat strtobin.c
#include <stdio.h>
#include <stdlib.h>

int main(void)
{
  char *str = "00111010";

  printf("%s binary is %X hexadecimal\n",
    str, (unsigned int)strtoul(str, NULL, 2));
  return 0;
}
itsme@itsme:~/C$ ./strtobin
00111010 binary is 3A hexadecimal

And then you can use fwrite() to write 0x3A to the file. It's 1 byte containing all 8 bits.

EDIT: You're going to have to familiarize yourself with bit operations to work with this a lot. For instance, to grab the least significant bit you could do int lsb = 0x3a & 1; and if you want the next least one you'd have to do int nextlsb = (0x3a & 2) >> 1;

It's definitely possible to do this in C, you just need to know what you're doing.