(PHP 4 >= 4.0.2, PHP 5)
ldap_compare — Compare value of attribute found in entry specified with DN
   Compare value of attribute
   with value of same attribute in an LDAP directory entry.
  
link_identifierAn LDAP link identifier, returned by ldap_connect().
dnThe distinguished name of an LDAP entity.
attributeThe attribute name.
valueThe compared value.
   Returns TRUE if value matches otherwise returns
   FALSE. Returns -1 on error.
  
The following example demonstrates how to check whether or not given password matches the one defined in DN specified entry.
Example #1 Complete example of password check
<?php
$ds=ldap_connect("localhost");  // assuming the LDAP server is on this host
if ($ds) {
    // bind
    if (ldap_bind($ds)) {
        // prepare data
        $dn = "cn=Matti Meikku, ou=My Unit, o=My Company, c=FI";
        $value = "secretpassword";
        $attr = "password";
        // compare value
        $r=ldap_compare($ds, $dn, $attr, $value);
        if ($r === -1) {
            echo "Error: " . ldap_error($ds);
        } elseif ($r === true) {
            echo "Password correct.";
        } elseif ($r === false) {
            echo "Wrong guess! Password incorrect.";
        }
    } else {
        echo "Unable to bind to LDAP server.";
    }
    ldap_close($ds);
} else {
    echo "Unable to connect to LDAP server.";
}
?>
ldap_compare() can NOT be used to compare BINARY values!