libmagic.h example

libmagic_example.c

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

int main(void)
{
    char *actual_file = "/file/you/want.yay";
    const char *magic_full;
    magic_t magic_cookie;
	
    /* MAGIC_MIME tells magic to return a mime of the file, 
       but you can specify different things	*/
    magic_cookie = magic_open(MAGIC_MIME);
	
    if (magic_cookie == NULL) {
        printf("unable to initialize magic library\n");
        return 1;
    }
	
    printf("Loading default magic database\n");
    
    if (magic_load(magic_cookie, NULL) != 0) {
        printf("cannot load magic database - %s\n", magic_error(magic_cookie));
        magic_close(magic_cookie);
        return 1;
    }
	
    magic_full = magic_file(magic_cookie, actual_file);
    printf("%s\n", magic_full);
    magic_close(magic_cookie);
    return 0;
}

Warning: magic_load(magic_cookie, NULL) wont pass memory debugger like electricfence.

You have to provide a filename or libmagic tries a malloc(0) which may provide unpredictable result later. magic_load(session->magic,"/usr/share/misc/magic.mgc") pass.

Warning: magic_load(magic_cookie, NULL) wont pass memory debugger like electricfence.

You have to provide a filename or libmagic tries a malloc(0) which may provide unpredictable result later. magic_load(session->magic,"/usr/share/misc/magic.mgc") pass.

malloc(0) is perfectly fine and allowed. Passing NULL to magic_load() is the recommended way of doing this. Do not pass a filename if you want your code to use the default file and be portable.

Hello, thanks for this example, when I run it it gives this output:
collect2: error: ld returned 1 exit status

Hello, thanks for this example, when I run it it gives this output:
collect2: error: ld returned 1 exit status

Fixed with gcc -g test.c -lmagic

Hello. It's a very clear and useful example. Thanks.
Isn't it necessary to free the memory allocated by magic_file function (memory pointed by magic_full in this example)? Would magic_close take care of that (and all the subsequent calls of magic_file)?

---

apparently, it is not necessary. I got this runtime error:
free(): double free detected in tcache 2

Hello. It's a very clear and useful example. Thanks. Isn't it necessary to free the memory allocated by magic_file function (memory pointed by magic_full in this example)?

No, libmagic is managing its own storage and magic_file returns a pointer into that storage. magic_close() probably frees the heap.
The manpage gives the declaration const char *magic_file(magic_t cookie, const char *filename);, the const qualifier seems to mean that they retains «ownership» over the data and so the storage.