how to store binary string , in the binary form, in a file?

Question

Hello all, i have a problem on storing binary string. How can i store binary string "100010101010000011100", in the binary form, in a file using C ?

Apart from just one string, if i have two strings, how can i store these two strings together? Thanks for your help.

Answer 1

char *p;

p="100010101010000011100"

orr

char A[]="100010101010000011100"

or

if alot of binary input

define max1 100

define max2 100

{ char *p; char A[max1][max2];

for(;*p!='\0';++p)

gets(p); A[i]=p;

Answer 2

Erm, I am not sure if I understand your question. Are you asking HOW to store a string in a file using C or are you asking the best way to encode binary data for file storage?

If the former, I suggest the following resources:

• C File I/O
• WriteFile function (MSDN)

If the latter, then there are numerous encoding methods and standards, but frankly I don't see why you don't just store your binary string as-is.

EDIT: Think about it again, the obvious solution would be to convert your binary number into an integer or hex and store that.

Answer 3

Open the file for writing in binary mode.

Convert your binary string into integer and write that to the file

Answer 4

You can stuff 8 bits into an unsigned char variable and write that to the file.

unsigned char ch=0;
char bin[] = "100010101010000011100";
int i=0;

while(bin[i]) {
  if(i%8 == 0) {
    // write ch to file.
    ch = 0;
  }else {
   ch = ch | (bin[i] - '0');
   ch = ch << 1;
  }
  i++;
}

Answer 5

This one supports binary strings of arbitrary lengths, but of course has many deficiencies, esp. when considering reading back from file. :) Should be good enough for a starter, though.

#include <string.h>
#include <fcntl.h>
#include <stdlib.h>

char A[]="111100000000111111";

int main() {
    unsigned int slen = strlen(A);
    unsigned int len = slen/8 + !!(slen%8);
    unsigned char * str = malloc(len);

    unsigned int i;
    for (i = 0; i < slen; i++) {
        if (!(i%8))
            str[i/8] = 0;
        str[i/8] = (str[i/8]<<1) | (A[i] == '1' ? 1 : 0);
    }
    if (slen%8)
        str[len-1] <<= (8-slen%8);

    int f = open("test.bin", O_CREAT | O_TRUNC | O_WRONLY, S_IRWXU);
    write(f, str, len);
    close(f);
};