Passing variable between functions - php - php

Question

Below is an edited version of my actual code:
<?php
include ('login_info.php');
class modernCMS {
var $host;
var $username;
var $password;
var $db;
var $url;
function connect(){
$con = mysql_connect($this->host, $this->username, $this->password);
mysql_select_db($this->db, $con) or die(mysql_error());
mysql_set_charset('utf8');
}
function get_coordinates(){
$sql ="select lat, lng from postcodes LIMIT 1;";
$res = mysql_query($sql) or die(mysql_error());
while($row = mysql_fetch_assoc($res)){
$lat = $row['lat'];
$lng = $row['lng'];
}
}
function get_name(){
$sql ="select name from places WHERE lat=$lat AND lng=$lng LIMIT 1;";
$res = mysql_query($sql) or die(mysql_error());
while($row = mysql_fetch_assoc($res)){
$name = $row['name'];
echo $name;
}
}
?>
Then within a separate document i have an include for the file above. I call the function get name using the following:
<?=$obj->get_name()?>
get_name actually contains a calculation for calculating the distance between two points however because its a lengthy calculation i have left it out of the example above.
Its important that i can just use $obj->get_name() to get the output for $lat and $lng

Answer 1

Functions operate within function scope, so the variables that you've set in get_coordinates() are local variables. To create global variables, you can use the global keyword:
<?php
function get_coordinates()
{
global $lat, $lng;
$lat = 25;
$lng = 5;
}
function display_coordinates()
{
global $lat, $lng;
echo $lat;
echo $lng;
}
get_coordinates();
display_coordinates();
Or $GLOBALS array:
<?php
function get_coordinates()
{
$GLOBALS['lat'] = 25;
$GLOBALS['lng'] = 5;
}
function display_coordinates()
{
echo $GLOBALS['lat'];
echo $GLOBALS['lng'];
}
get_coordinates();
display_coordinates();
However, this may not be the best way to set/access these variables because any function can change their state at any time, and you must call one function to set them before calling the other to display them. If you can describe your specific goal, you might be able to get better advice.
One better way to accomplish this is to use a class, and pass the object where you need it (this simple example does not demonstrate proper encapsulation, but is a good starting point):
<?php
class Coordinates {
public $lat;
public $lng;
public function __construct($lat, $lng) {
$this->lat = $lat;
$this->lng = $lng;
}
public function display_coordinates() {
echo $this->lat . "\n";
echo $this->lng . "\n";
}
}
function get_coordinates() {
return new Coordinates(25, 5);
}
$coords = get_coordinates();
$coords->display_coordinates();
function output_coordinates($coordinates) {
$coordinates->display_coordinates();
}
output_coordinates($coords);
Another way that is commonly used in PHP is to pass things in associative arrays (arrays with strings for indexes). I don't prefer this usually, because the array does not declare what it intends to hold, but it is an option:
<?php
function get_coordinates() {
return array('lat' => 25, 'lng' => 5);
}
function output_coordinates($coordinates) {
echo $coordinates['lat'] . '\n';
echo $coordinates['lng'] . '\n';
}
$coords = get_coordinates();
output_coordinates($coords);

Answer 2

You're running into a scoping issue. The variables are only available to the function that declared them. To make them available, you can either pass the variables to the function explicitly (you need to make sure you always call get_coordinates() before display_coordinates() though, otherwise you'll have undefined values), or using global variables (bad idea).
The best method is probably to make a class for it (although it depends on how you intend to use it). Your variables will always be in scope, and you won't run the risk of trying to run the display_coordinates() function before you've initialized the variables.
class Coordinate
{
// These are the variables where the coords will be stored.
// They are available to everything within the {}'s after
// "class Coordinate" and can be accessed with
// $this->_<varname>.
protected $_lat;
protected $_long;
// This is a special function automatically called when
// you call "new Coordinate"
public function __construct($lat, $long)
{
// Here, whatever was passed into "new Coordinate" is
// now stored in our variables above.
$this->_lat = $lat;
$this->_long = $long;
}
// This takes the values are stored in our variables,
// and simply displays them.
public function display()
{
echo $this->_lat;
echo $this->_long;
}
}
// This creates a new Coordinate "object". 25 and 5 have been stored inside.
$coordinate = new Coordinate(25, 5); // 25 and 5 are now stored in $coordinate.
$coordinate->display(); // Since $coordinate already "knows" about 25 and 5
// it can display them.
// It's important to note, that each time you run "new Coordinate",
// you're creating an new "object" that isn't linked to the other objects.
$coord2 = new Coordinate(99, 1);
$coord2->display(); // This will print 99 and 1, not 25 and 5.
// $coordinate is still around though, and still knows about 25 and 5.
$coordinate->display(); // Will still print 25 and 5.
You should read up on Variable Scope and Classes and Objects to understand more about this.
To put this together with your original code, you would do something like this,
function get_coordinates()
{
return new Coordinate(25, 5);
}
function display_coordinates($coord)
{
$coord->display();
}
$c = get_coordinates();
display_coordinates($c);
// or just "display_coordinates(get_coordinates());"
Edit after question updated
There are a few bad practices in your code, but here's some quick steps to get what you want.
// Copy the Coordinate class from my answer above, but add two new
// lines before the final "}"
public function getLatitude() { return $this->_lat; }
public function getLongitude() { return $this->_long; }
// Put the Coordinate class definition before this line
class modernCMS {
/////
// In your code, after this line near the top
var $url;
// Add this
var $coord;
/////
// In your get_coordinates(), change this...
$lat = $row['lat'];
$lng = $row['lng'];
// To this...
$this->coord = new Coordinate($lat, $lng);
/////
// In your get_name(), add two lines to the start of your function.
function get_name(){
$lat = $this->coord->getLatitude();
$lng = $this->coord->getLongitude();
Unrelated to your question, but you should also read about "SQL Injection" as query in get_name() is vulnerable. Not a big deal here, since the data comes from your other query anyway, but still good practice not to use parameters directly in a query string.

Answer 3

What about Session?
https://www.php.net/manual/en/reserved.variables.session.php
Creating New Session
session_start();
/*session is started if you don't write this line can't use $_Session global variable*/
$_SESSION["newsession"]=$value;
Getting Session
session_start();
/*session is started if you don't write this line can't use $_Session global variable*/
$_SESSION["newsession"]=$value;
/*session created*/
echo $_SESSION["newsession"];
/*session was getting*/
Updating Session
session_start();
/*session is started if you don't write this line can't use $_Session global variable*/
$_SESSION["newsession"]=$value;
/*it is my new session*/
$_SESSION["newsession"]=$updatedvalue;
/*session updated*/
Deleting Session
session_start();
/*session is started if you don't write this line can't use $_Session global variable*/
$_SESSION["newsession"]=$value;
unset($_SESSION["newsession"]);
/*session deleted. if you try using this you've got an error*/

Answer 4

One way of doing it:
function get_coordinates(&$lat, &$lng)
{
$lat = 25;
$lng = 5;
}
function display_coordinates($lat, $lng)
{
echo $lat;
echo $lng;
}
$lat = 0;
$lng = 0;
// assign values to variables
get_coordinates( $lat, $lng );
// use function to display them...
display_coordinates ($lat, $lng);

Answer 5

Create a Coordinate.class.php file:
<?php
class Coordinate {
var $latitude;
var $longitude;
public function getLatitude() {
return $this->latitude;
}
protected function setLatitude($latitude) {
$this->latitude = floatval($latitude);
}
public function getLongitude() {
return $this->longitude;
}
protected function setLongitude($longitude) {
$this->longitude = floatval($longitude);
}
public function __construct() {
// Overload
if (func_num_args() == 2) {
$this->setLatitude(func_get_arg(0));
$this->setLongitude(func_get_arg(1));
}
// Default
else {
$this->setLatitude(0);
$this->setLongitude(0);
}
}
public function displayCoordinate() {
printf("Latitude: %.2f, Longitude: %.2f\n",
$this->getLatitude(),
$this->getLongitude());
}
}
function main() {
$c = new Coordinate (25, 5);
$c->displayCoordinate();
}
main();
?>

Answer 6

Change of another post.. I think the better way:
function get_coordinates()
{
return array(
"lat" => 25,
"lng" => 5
);
}
function display_coordinates($latLongArray)
{
echo $latLongArray['lat'];
echo $latLongArray['lng'];
}
// assign values to variables
$latLongArray = get_coordinates();
// use function to display them...
display_coordinates ($latLongArray);