PHP: variable interpolation issue - php

Question

I am having a real issue with variable interpolation - maybe what I'm trying to do shouldn't be done? Sample code (IRL, the array is 70+ elements):
<form submit>
$_POST['A']; //returns 12
$_POST['B']; //returns 8
<query to get orig field values>
$OrigA = $row->appA; //returns 12
$OrigB = $row->appB; //return 14
<array of names>
$fields = array ("A", "B");
$querystr = "INSERT INTO tblEditHist VALUES ";
foreach ($fields as $field) {
$orig = "Orig" . $field;
$new = "\$_POST['app" . $field . "']";
$fieldname = "app" . $field;
if (${$orig} != ${$new}) { $querystr .= "('default', $applID, '$fieldname', '${$orig}', '${$new}', '$DateTimeReq', '$hvid'), "; };
}
print "querystr: " . $querystr . "\n";
The part if (${$orig} != ${$new}) is what's not working as I would expect. When I print it out to screen with print "DEBUG: if (${$orig} != ${$new}) { $querystr .= \"('default', $applID, '$fieldname', '{$orig}', '{$new}', '$DateTimeReq', '$hvid')\"; };<br />\n";, I see my variables aren't interpolating properly, my debug print says: DEBUG: if ( != ) { .... It should interpolate to (for B): DEBUG: if (8 != 14) { ...
I have tried various combinations of dollar signs and braces, but I don't seem to be making headway. Am I barking up the wrong tree here?
Thanks as always!!

Answer 1

Like this : No interpolation POST variable
<?php
$A = $_POST['A'] = 12; //returns 12
$B = $_POST['B'] = 8; //returns 8
$OrigA = 12; //returns 12
$OrigB = 14; //return 14
$fields = array ("A", "B");
$querystr = "INSERT INTO tblEditHist VALUES ";
foreach ($fields as $field) {
$orig = "Orig" . $field;
$fieldname = "app" . $field;
if (${$orig} != ${$field}) { $querystr .= "('default', $applID, '$fieldname', '${$orig}', '${$new}', '$DateTimeReq', '$hvid'), "; };
}
print "querystr: " . $querystr . "\n";
?>
See http://codepad.org/Ecro0PyG

Answer 2

I don't get all your questions but maybe this code could help you a little (you can use your $_POST var instead of mine $post, that is just to show result and debug):
$post = array();
$post['A'] = 12;
$post['B'] = 8;
$OrigA = 12;
$OrigB = 14;
$fields = array ("A", "B");
$querystr = "INSERT INTO tblEditHist VALUES ";
foreach ($fields as $field) {
$origVarName = 'Orig'.$field;
echo '$$origVarName = '.$$origVarName.'<br/>';
echo '$post[$field] = '.$post[$field].'<br/>';
$fieldname = "app" . $field;
if ($$origVarName != $post[$field]) {
echo $field.' NOT EQUAL!';
} else {
echo $field.' EQUAL!';
}
}