PHP - array_push() expects parameter 1 to be array, null given in - php

Question

I'm currently experiencing issues where array_push() is not working. I have ensured the arrays are directly accessible and declared correctly. Yet I'm still receiving these warnings and the values are not being pushed onto the array.
Here is my code:
include('../connstr.inc');
$email=$_REQUEST["email"];
$datafile=$_REQUEST["datafile"];
$email_safe=preg_replace("/[^a-zA-Z]/","_",$email);
$path="../uploaded_data";
$xml = simplexml_load_file("{$path}/{$email_safe}/{$datafile}.xml");
// Retreive data details for specified activity
$lapCount = $xml->Activities->Activity->Lap->count();
// Lap Variables
$totalTime = array(); $distance = array(); $maxSpeed = array();
$calories = array(); $intensity = array(); $trigMethod = array();
$avgSpeed = array();
// Convert filename to DateTime format
$datafile = convertID($datafile);
$datafile = date('Y-m-d H:i:s', strtotime($datafile));
// Variables for accurate distance calculations
$polarDistance = true;
$lapID;
$totalLapDistance;
$firstPoint = array();
$secondPoint = array();
// Collect details for each lap
for($x = 0; $x < $lapCount; $x++) {
$totalLapDistance = 0;
$lapNumber = $x+1;
$totalTime[$x] = $xml->Activities->Activity->Lap[$x]->TotalTimeSeconds;
$distance[$x] = $xml->Activities->Activity->Lap[$x]->DistanceMeters;
$maxSpeed[$x] = $xml->Activities->Activity->Lap[$x]->MaximumSpeed;
$calories[$x] = $xml->Activities->Activity->Lap[$x]->Calories;
$intensity[$x] = $xml->Activities->Activity->Lap[$x]->Intensity;
$trigMethod[$x] = $xml->Activities->Activity->Lap[$x]->TriggerMethod;
$avgSpeed[$x] = $xml->Activities->Activity->Lap[$x]->Extensions->LX->AvgSpeed;
// Store activity details into the 'detail' table
$sqlLap = "INSERT INTO lap (lapDate,lapNumber,TotalTime,distance,maxSpeed,avgSpeed,calories,intensity,trigMethod) VALUES (\"$datafile\",\"$lapNumber\",\"$totalTime[$x]\",\"$distance[$x]\",\"$maxSpeed[$x]\",\"$avgSpeed[$x]\",\"$calories[$x]\",\"$intensity[$x]\",\"$trigMethod[$x]\")";
$runLap = mysql_query($sqlLap) or die("unable to complete INSERT action:$sql:".mysql_error());
// Trackpoint variables
$altitude = array(); $tDistance = array(); $latitude = array();
$longitude = array(); $speed = array(); $pointTime = array();
// Retreive lapID
$lapID = getLapID();
// Find how many tracks exist for specified lap
$trackCount = $xml->Activities->Activity->Lap[$x]->Track->count();
$trackpointTotalCount = 1;
for($t = 0; $t < $trackCount; $t++) {
// Find out how many trackpoints exist for each track
$trackpointCount = $xml->Activities->Activity->Lap[$x]->Track[$t]->Trackpoint->count();
// Collect details for each specificied track point
for($tp = 0; $tp < $trackpointCount; $tp++) {
$altitude[$tp] = $xml->Activities->Activity->Lap[$x]->Track[$t]->Trackpoint[$tp]->AltitudeMeters;
$tDistance[$tp] = $xml->Activities->Activity->Lap[$x]->Track[$t]->Trackpoint[$tp]->DistanceMeters;
$pointTime[$tp] = $xml->Activities->Activity->Lap[$x]->Track[$t]->Trackpoint[$tp]->Time;
$latitude[$tp] = $xml->Activities->Activity->Lap[$x]->Track[$t]->Trackpoint[$tp]->Position->LatitudeDegrees;
$longitude[$tp] = $xml->Activities->Activity->Lap[$x]->Track[$t]->Trackpoint[$tp]->Position->LongitudeDegrees;
$speed[$tp] = $xml->Activities->Activity->Lap[$x]->Track[$t]->Trackpoint[$tp]->Extensions->TPX->Speed;
// Check Track point
if(checkTP($altitude[$tp], $tDistance[$tp], $latitude[$tp], $longitude[$tp], $speed[$tp])) {
// Check if accurate distance should be calculated
if($polarDistance) {
$aa = $latitude[$tp];
$bb = $longitude[$tp];
$cc = $altitude[$tp];
if($tp == 0) {
array_push($firstPoint, $aa, $bb, $cc);
} else if($tp != 0) {
array_push($secondPoint, $aa, $bb, $cc);
}
printArray($firstPoint);
printArray($secondPoint);
// Add distance between trackpoints to total lap distance
$totalLapDistance += calcDistance($firstPoint, $secondPoint);
}
// Insert current trackpoint data into 'trackpoint' table
$sqlTC = "INSERT INTO trackpoint (tpDate,tpNumber,altitude,distance,latitude,longitude,speed,pointTime) VALUES (\"$datafile\",\"$trackpointTotalCount\",\"$altitude[$tp]\",\"$tDistance[$tp]\",\"$latitude[$tp]\",\"$longitude[$tp]\",\"$speed[$tp]\",\"$pointTime[$tp]\")";
$runTC = mysql_query($sqlTC) or die("unable to complete INSERT action:$sql:".mysql_error());
}
$trackpointTotalCount++;
if($polarDistance) {
if($tp != 0) {
unset($firstPoint);
$firstPoint = &$secondPoint;
unset($secondPoint);
}
}
}
}
if($polarDistance) {
if($tp != 0) {
// Update lap with more accurate distance
echo $totalLapDistance . '<br />';
$sqlUlap = "UPDATE lap SET accDistance='$totalLapDistance' WHERE lapID = '$lapID' ";
$runUlap = mysql_query($sqlUlap) or die("unable to complete UPDATE action:$sql:".mysql_error());
}
}
}
I didn't include all of the code below as there is quite a lot and I very much doubt it's relevant.
The warnings themselves only appear when trying to push a variable onto $secondPoint:
array_push($secondPoint, $aa, $bb, $cc);
However values are not being pushed onto either of the variables ($firstPoint, $secondPoint)
As a test I did echo $aa,bb and $cc and they did contain correct values.
Anybody have an idea of what I'm doing wrong?
EDIT: I have showed more of the code as I do use these arrays later, however this should not affect how the values are initially pushed? Below is some code which may affect it, namely the assign by reference?
if($polarDistance) {
if($tp != 0) {
unset($firstPoint);
$firstPoint = &$secondPoint;
unset($secondPoint);
}
}

Answer 1

That unset($secondPoint) will probably do it.
Try this instead:
if($polarDistance) {
if($tp != 0) {
$firstPoint = $secondPoint;
$secondPoint = array();
}
}