These functions are used to sort lists of entries and values retrieved from an LDAP server. ldap_sort_entries() is used to sort a chain of entries retrieved from an LDAP search call either by DN or by some arbitrary attribute in the entries. It takes ld, the LDAP structure, which is only used for error reporting, chain, the list of entries as returned by ldap_search_s(3LDAP) or ldap_result(3LDAP). attr is the attribute to use as a key in the sort or NULL to sort by DN, and cmp is the comparison function to use when comparing values (or individual DN components if sorting by DN). In this case, cmp should be a function taking two single values of the attr to sort by, and returning a value less than zero, equal to zero, or greater than zero, depending on whether the first argument is less than, equal to, or greater than the second argument. The convention is the same as used by qsort(3C), which is called to do the actual sorting.

ldap_sort_values() is used to sort an array of values from an entry, as returned by ldap_get_values(3LDAP). It takes the LDAP connection structure ld, the array of values to sort vals, and cmp, the comparison function to use during the sort. Note that cmp will be passed a pointer to each element in the vals array, so if you pass the normal char ** for this parameter, cmp should take two char **'s as arguments (that is, you cannot pass strcasecmp or its friends for cmp). You can, however, pass the function ldap_sort_strcasecmp() for this purpose.

For example:

	LDAP *ld;
	LDAPMessage *res;
	/* ... call to ldap_search_s(), fill in res, retrieve sn attr ... */

	/* now sort the entries on surname attribute */
	if ( ldap_sort_entries( ld, &res, "sn", ldap_sort_strcasecmp ) != 0 )
		ldap_perror( ld, "ldap_sort_entries" );

See attributes(5) for a description of the following attributes:

ldap(3LDAP), ldap_search(3LDAP), ldap_result(3LDAP), qsort(3C), attributes(5)

The ldap_sort_entries() function applies the comparison function to each value of the attribute in the array as returned by a call to ldap_get_values(3LDAP), until a mismatch is found. This works fine for single-valued attributes, but may produce unexpected results for multi-valued attributes. When sorting by DN, the comparison function is applied to an exploded version of the DN, without types. The return values for all of these functions are declared in the <ldap.h> header file. Some functions may allocate memory which must be freed by the calling application.