Thread: how can i manipulate a file in binary mode?

hi take a look at this source code (it doesn't have bugs):

Code:

#include <stdio.h>
#include <stdlib.h>

int main( void )
{
    FILE *fp;
    int c;

    if ( (fp = fopen("TEXT.TXT", "rb")) == NULL)
    {
        fprintf(stderr, "Error opening file.");
        exit(1);
    }
    while ((c = fgetc(fp)) != EOF)
    {
        printf("%c ", c);
    }
    fclose(fp);
    return 0;
}

(in TEXT.TXT there's one line of the alphabet's characters(abcd...))

it runs fine but fgetc gives me the actual letters in the text file.
what i wanted it to print was the binary values byte by byte (like 01011001)
how can i achieve that?

Opening a file in "binary mode" doesn't make things "binary", it just ensures that the raw bytes are read as-is, whereas "text mode" will do implementation-defined conversions, e.g., translating 0xd 0xa combinations into a single 0xa on windows. On *nix OSes, there's no difference between text and binary modes.

You're seeing characters because you're printing with the %c format. If you used the %d format you'd see the decimal value. With %x you would see hex. There is no standard format for binary. If you really want to see the bits, you can write your own function to print them.

Code:

#include <stdio.h>
#include <stdlib.h>
 
void binary(char byte) {
    unsigned char mask = 0x80;
    for ( ; mask; mask >>= 1)
        putchar(byte & mask ? '1' : '0');
}

int main( void )
{
    FILE *fp;
    int c;
 
    if ( (fp = fopen("TEXT.TXT", "rb")) == NULL)
    {
        fprintf(stderr, "Error opening file.");
        exit(1);
    }

    while ((c = fgetc(fp)) != EOF)
    {
        binary(c);
        putchar(' ');
    }

    putchar('\n');
    fclose(fp);
    return 0;
}

Originally Posted by algorism

Opening a file in "binary mode" doesn't make things "binary", it just ensures that the raw bytes are read as-is, whereas "text mode" will do implementation-defined conversions, e.g., translating 0xd 0xa combinations into a single 0xa on windows. On *nix OSes, there's no difference between text and binary modes.

You're seeing characters because you're printing with the %c format. If you used the %d format you'd see the decimal value. With %x you would see hex. There is no standard format for binary. If you really want to see the bits, you can write your own function to print them.

Code:

#include <stdio.h>
#include <stdlib.h>
 
void binary(char byte) {
    unsigned char mask = 0x80;
    for ( ; mask; mask >>= 1)
        putchar(byte & mask ? '1' : '0');
}

int main( void )
{
    FILE *fp;
    int c;
 
    if ( (fp = fopen("TEXT.TXT", "rb")) == NULL)
    {
        fprintf(stderr, "Error opening file.");
        exit(1);
    }

    while ((c = fgetc(fp)) != EOF)
    {
        binary(c);
        putchar(' ');
    }

    putchar('\n');
    fclose(fp);
    return 0;
}

I've read the book teach yourself c in 21 days from sams publishing and it didn't cover what you just did in the binary function. can someone explain to me what he did? also i need a book recommendation for more advanced c coding so i can understand these source codes better obviously the book i read doesn't just cut it