c - Storing a two-bit binary in char -


so i'm working on program takes file of characters , turns these file of characters of binary numbers. have able read these characters (the binary characters) , turn them denoted characters.

so encoding , decoding file.

so have file 4 characters: '@', '/n', ':', ' '. (last 1 space)

so reason want have bunch of ascii pictures want store in smaller files.

i have been told can use unsigned char, set 0, read file characters described above, , use bitwise operators assign values read unsigned char , each 4 characters read (because each character 8 bites , these can turned 2 bites each , stored in 1 character, hence 4 characters in 1 char) append (add) each number char.

any appreciated!

the code have this: 

#include <stdio.h> #include <stdlib.h> #include <string.h>  file *inputfile; file *outputfile;  int encodebinary[4] = {0x00, 0x01, 0x02, 0x03}; char encodechars[4] = {':', '@', '\n', ' '};  //reads file , creates encoded file void encode(const char * infile, const char * outfile) {      inputfile = fopen(infile, "r");     outputfile = fopen(outfile, "w");     char linebuffer[bufsiz];     int size = 0;     char temp = 0;      if(inputfile == null)     {         perror("error while opening file.\n");         exit(exit_failure);     }      while(fgets(linebuffer, sizeof(linebuffer), inputfile))     {         for(int = 0; linebuffer[i] != 0; i++)         {              //adds 4 different characters char before adding character file             if(size < 4) {                 if(linebuffer[i] == encodechars[0])                 {                  }                 else if(linebuffer[i] == encodechars[1])                 {                  }                 else if(linebuffer[i] == encodechars[2])                 {                  }                 else if(linebuffer[i] == encodechars[3])                 {                  }                  size++;             } else {                 size = 0;                 temp = 0;              }         }     }      fclose(inputfile);     fclose(outputfile);  }

would appreciate if come examples how add bits read in temp char. have no idea how can add numbers char moved in such way , added in such way represent old numbers , new. i'm thinking can bitshift number 3 times left, 01 becomes 0100.

instead of using bitfields, use << , >> operators , bitwise & , | manipulate bits directly,

encode,

unsigned char accum;  if(size>0) accum = encodechars[0] << 6 if(size>1) accum |= encodechars[0] << 4 if(size>2) accum |= encodechars[0] << 2 if(size>3) accum |= encodechars[0] if(linebuffer[i] accum

decode,

char array[4]; if(size>0) array[0] = decodechars[ (accum >> 6) &0x3 ]; if(size>1) array[1] = decodechars[ (accum >> 4) &0x3 ]; if(size>2) array[2] = decodechars[ (accum >> 2) &0x3 ]; if(size>3) array[3] = decodechars[ (accum) &0x3  ];

and read big-endian vs. little-endian understand element storage order.


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