CODEWITHSUNDEEP
cbinarybyte
adelbertc
adelbertc

Reputation: 7320

Reading "pure" bytes in C

I was wondering.. how do you read bytes one at a time from a binary file? As an example, I'd like to read bytes one at a time from some binary file and then write those exact bytes to some output file (basically a very basic implementation of the cp command). My current C code looks like this:

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

int main(int argc, char**argv)
{
    if (argc != 2) {
        fprintf(stderr, "Usage: %s <output file>\n", argv[0]);
        return 1;
    }

    FILE *outfile;
    outfile = fopen(argv[1], "w");

    unsigned char c;
    char temp;
    int tracker = 0;
    // Use temp because unsigned char will never be EOF
    while ((temp = getchar()) != EOF) {
        c = (unsigned char) temp;
        fprintf(outfile, "%c", c);
    }
fclose(outfile);
return 0;
}

I run the program like this: ./main output.au < sample.au (.au is an audio file)

However, all I get in the output.au file is a bunch of "^@" repeated over and over. I can play the sample.au audio file fine, but not the output.au. I've also (somewhat pointlessly) done a diff on the two files, and as expected they come out differently.

Help? Thanks! -kstruct

UPDATE Thanks for the reply everyone.. my code now looks like:

outfile = fopen(argv[1], "wb");

int c;
while ((c = getchar()) != EOF) {
    fprintf(outfile, "%c", c);
}

Upvotes: 2

Views: 3093

Answers (3)

fdk1342
fdk1342

Reputation: 3564

There are several things that need to get fixed: 1) Reopen STDIN as binary. freopen(NULL, "rb", stdin); 2) Open the outfile as: fopen(argv[1], "wb"); 3) temp needs to be of type int.

Upvotes: 2

pmg
pmg

Reputation: 108938

getchar() returns an int. You assign that int to a variable of type char thereby losing information. Don't do that.

Declare temp as int, and go get rid of the cast.

Upvotes: 7

Joshua
Joshua

Reputation: 43280

make the following corrections:

- outfile = fopen(argv[1], "w");
+ outfile = fopen(argv[1], "wb");


- c = (unsigned char) temp;
+ c = (unsigned char) (char) temp;

Upvotes: 0

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