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Error::getPrevious — Returns previous Throwable
Returns previous Throwable (the third parameter of Error::__construct()).
This function has no parameters.
   Returns the previous Throwable if available 
   or NULL otherwise.
  
Example #1 Error::getPrevious() example
Looping over, and printing out, error trace.
<?php
class MyCustomError extends Error {}
function doStuff() {
    try {
        throw new InvalidArgumentError("You are doing it wrong!", 112);
    } catch(Error $e) {
        throw new MyCustomError("Something happened", 911, $e);
    }
}
try {
    doStuff();
} catch(Error $e) {
    do {
        printf("%s:%d %s (%d) [%s]\n", $e->getFile(), $e->getLine(), $e->getMessage(), $e->getCode(), get_class($e));
    } while($e = $e->getPrevious());
}
?>
The above example will output something similar to:
/home/bjori/ex.php:8 Something happened (911) [MyCustomError] /home/bjori/ex.php:6 You are doing it wrong! (112) [InvalidArgumentError]