CODEWITHSUNDEEP
cbinaryascii
user1684072
user1684072

Reputation: 169

How can I check if file is text (ASCII) or binary in C

I need to write C code that checks to see if a file is text(ASCII) or Binary

Could someone help? Thanks

Upvotes: 6

Views: 7573

Answers (3)

user3303210
user3303210

Reputation: 137

You can use libmagic. The code below will show you roughly the way the "file" command does it. (The code below is quick and dirty -- it probably needs to be cleaned up.)

#include <string.h>
#include <magic.h>
#include <stdio.h>


//------------------------------------------------------------------------------
struct magic_set * prep_magic(int flags)
{
struct magic_set *magic = magic_open(flags);
const char *errstring;
int action = 0;
const char *magicfile = NULL;

if (magicfile == NULL)
    magicfile = magic_getpath(magicfile, action);

if (magic == NULL)
    {
        printf("Can't create magic");
        return NULL;
    }
if (magic_load(magic, magicfile) == -1)
    {
        printf("%s", magic_error(magic));
        magic_close(magic);
        return NULL;
    }
if ((errstring = magic_error(magic)) != NULL)
        printf("%s\n", errstring);

return magic;
/* END FUNCTION prep_magic */ }
//------------------------------------------------------------------------------
int main(int argc, char **argv)
{
int flags = 0;
struct magic_set *msetptr = NULL;

const char *testfile = (char *)"/etc/motd";


msetptr = prep_magic(flags);
if( msetptr == NULL )
    printf("no mset ptr\n");

const char *typer;
typer = magic_file( msetptr, testfile );
printf("typer = %s\n", typer );

return 0;
/* END PROGRAM */ }

Upvotes: 1

Dietrich Epp
Dietrich Epp

Reputation: 213318

Typical method is to read the first several hundred bytes and look for ASCII NUL.

If the file contains NUL, it is definitely a binary file. Most binary files do contain NUL bytes, but text files should never contain NUL bytes.

#include <string.h>
bool is_binary(const void *data, size_t len)
{
    return memchr(data, '\0', len) != NULL;
}

Be warned that this is a heuristic. In other words, it will be wrong sometimes.

Upvotes: 6

Alexey Frunze
Alexey Frunze

Reputation: 62048

Read all characters and see if all of them are ASCII, that is, with codes from 0 to 127 inclusive.

Some tools determine whether a file is a text file or a binary file by just checking whether or not it has any byte with code 0.

Clearly, if you apply both of these methods, you will get different results for some files, so, you have to define what it is exactly that you're looking for.

Upvotes: 3

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