How to get extended attributes of a file(UNIX/C)?

Question

When I type ls -l in the command line, sometimes an @ or + symbol comes up alongside the file permissions(btw, I am on OS X), as shown below:

-rw-r-----@  1 john  staff      6731 Sep 28 01:10 mutations.txt
drwxr-xr-x+ 71 john  staff      2414 Mar 25 18:16 ..

I know how to get the permission bits using the stat structure, but I don't think these extended permission values are there. Can someone point me in the right direction as to how to obtain these values via a C or POSIX API?

EDIT:

I attempted the following:

#include <sys/types.h>
#include <sys/xattr.h>
#include <sys/types.h>

int main () {
    char  l[1024];
    listxattr("/Users/john/desktop/mutations.txt", l, 1024,  XATTR_SHOWCOMPRESSION);

    printf("%s\n", l);
}

and got as output:

com.apple.metadata:kMDItemWhereFroms

Still trying to understand how to convert this to an @ or +?

Answer 1

Following is some code I scraped off of the official implementation of ls given by Apple you will find here. The code is long so do CMD + F and search for "printlong".

#include <sys/types.h>
#include <sys/xattr.h>
#include <sys/types.h>
#include <sys/acl.h>
#include <stdio.h>

int main () {
    acl_t acl = NULL;
    acl_entry_t dummy;
    ssize_t xattr = 0;
    char chr;
    char * filename = "/Users/john/desktop/mutations.txt";

    acl = acl_get_link_np(filename, ACL_TYPE_EXTENDED);
    if (acl && acl_get_entry(acl, ACL_FIRST_ENTRY, &dummy) == -1) {
        acl_free(acl);
        acl = NULL;
    }
    xattr = listxattr(filename, NULL, 0, XATTR_NOFOLLOW);
    if (xattr < 0)
        xattr = 0;

    if (xattr > 0)
        chr = '@';
    else if (acl != NULL)
        chr = '+';
    else
        chr = ' ';

    printf("%c\n", chr);
 }

Depending on the file used, the output will be a blank, @, or + in exactly the same manner ls -l displays it. Hope this helps !