php-calling-class-test.php

/***********************************************************
******* SIMPLE TEST **/

class A {
     function t() {
         echo get_calling_class();
     }
}

class B {
     function x() {
         $a = new A;
         $a->t();
     }
}

$b = new B;
$b->x(); // prints B

php-calling-class.php

<?php

function get_calling_class() {
    
    //get the trace
    $trace = debug_backtrace();
    
    // Get the class that is asking for who awoke it
    $class = ( isset( $trace[1]['class'] ) ? $trace[1]['class'] : NULL );

    // +1 to i cos we have to account for calling this function
    for ( $i=1; $i<count( $trace ); $i++ ) {
        if ( isset( $trace[$i] ) && isset( $trace[$i]['class'] ) ) // is it set?
             if ( $class != $trace[$i]['class'] ) // is it a different class
                 return $trace[$i]['class'];
    }
}

Should be checking that the 'class' index exists, as well, before using it.