Print binary representation of file - c

Question

I need a function which will print out the binary representation of a read file like the xxd program in unix, but I want to make my own. Hexidecimal works just fine with %x but there is no built in format for binary. Anyone know how to do this?

Answer 1

I usually do not believe in answering these sorts of questions with full code implementations, however I was handed this bit of code many years ago and I feel obligated to pass it on. I have removed all the comments except for the usage, so you can try to figure out how it works yourself.
Code base 16
#include <stdio.h>
#include <ctype.h>
// Takes a pointer to an arbitrary chunk of data and prints the first-len bytes.
void dump (void* data, unsigned int len)
{
printf ("Size: %d\n", len);
if (len > 0) {
unsigned width = 16;
char *str = (char *)data;
unsigned int j, i = 0;
while (i < len) {
printf (" ");
for (j = 0; j < width; j++) {
if (i + j < len)
printf ("%02x ", (unsigned char) str [j]);
else
printf (" ");
if ((j + 1) % (width / 2) == 0)
printf (" - ");
}
for (j = 0; j < width; j++) {
if (i + j < len)
printf ("%c", isprint (str [j]) ? str [j] : '.');
else
printf (" ");
}
str += width;
i += j;
printf ("\n");
}
}
}
Output base 16 (Excerpt from first 512 bytes* of a flash video)
Size: 512
00 00 00 20 66 74 79 70 - 69 73 6f 6d 00 00 02 00 - ... ftypisom....
69 73 6f 6d 69 73 6f 32 - 61 76 63 31 6d 70 34 31 - isomiso2avc1mp41
00 06 e8 e6 6d 6f 6f 76 - 00 00 00 6c 6d 76 68 64 - ....moov...lmvhd
00 00 00 00 7c 25 b0 80 - 7c 25 b0 80 00 00 03 e8 - ....|%..|%......
00 0c d6 2a 00 01 00 00 - 01 00 00 00 00 00 00 00 - ...*............
00 00 00 00 00 01 00 00 - 00 00 00 00 00 00 00 00 - ................
00 00 00 00 00 01 00 00 - 00 00 00 00 00 00 00 00 - ................
00 00 00 00 40 00 00 00 - 00 00 00 00 00 00 00 00 - ....#...........
00 00 00 00 00 00 00 00 - 00 00 00 00 00 00 00 00 - ................
00 01 00 02 00 01 9f 38 - 74 72 61 6b 00 00 00 5c - .......8trak...\
I assume you already know how to tell the size of a file and read a file in binary mode, so I will leave that out of the discussion. Depending on your terminal width you may need to adjust the variable: width -- the code is currently designed for 80 character terminals.
I am also assuming that when you mentioned xxd in conjunction with "binary" you meant non-text as opposed to base 2. If you want base 2, set width to 6 and replace printf ("%02x ", (unsigned char) str [j]); with this:
{
for (int k = 7; k >= 0; k--)
printf ("%d", ((unsigned char)str [j] >> k) & 1);
printf (" ");
}
The required change is pretty simple, you just need to individually shift all 8 bits of your octet and mask off all but the least-significant bit. Remember to do this in an order that seems counter-intuitive at first, since we print left-to-right.
Output base 2 (Excerpt from first 512 bytes* of a flash video)
Size: 512
00000000 00000000 00000000 - 00100000 01100110 01110100 - ... ft
01111001 01110000 01101001 - 01110011 01101111 01101101 - ypisom
00000000 00000000 00000010 - 00000000 01101001 01110011 - ....is
01101111 01101101 01101001 - 01110011 01101111 00110010 - omiso2
01100001 01110110 01100011 - 00110001 01101101 01110000 - avc1mp
00110100 00110001 00000000 - 00000110 11101000 11100110 - 41....
01101101 01101111 01101111 - 01110110 00000000 00000000 - moov..
00000000 01101100 01101101 - 01110110 01101000 01100100 - .lmvhd
00000000 00000000 00000000 - 00000000 01111100 00100101 - ....|%
10110000 10000000 01111100 - 00100101 10110000 10000000 - ..|%..
00000000 00000000 00000011 - 11101000 00000000 00001100 - ......
*For the sake of simplicity, let us pretend that a byte is always 8-bits.

Answer 2

Depending on the language, assuming you have bitwise operations, which lets you act on each bit of a variable, you can do the following. Read the file into a buffer, or a line, if encoding is needed, force it to extended ASCII (8 bit/ 1 byte character) now, when you get the buffer, you loop from 7 to 0 and using the and bitwise and a shift to check each bit value, let me give an example in C:
// gcc -Wall -Wextra -std=c99 xxd.c
#include <stdio.h>
#include <string.h>
int main() {
// Whatever buffer size you chose.
char buffer[32];
//Feel free to replace stdin to a File Pointer, or any other stream
// Reading into a char, means reading each byte at once
while (!feof(stdin)) {
// Read at most buffer bytes. Since its ASCII 1 byte = 1 char.
fgets(buffer, sizeof(buffer), stdin);
// Iterate though each character in the string/buffer.
const size_t len = strlen(buffer);
for (size_t j = 0; j < len; j++) {
// Print the most significant bit first.
for (int i = 7; i >=0; i--) {
// Check if the i-th bit is set
printf(buffer[j] & (1 << i) ? "1" : "0");
}
}
}
return 0;
}