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Help with PHP Variable Scope

Posted on 2015-02-21
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Last Modified: 2015-02-22
I have a script that calls a function which runs a query and returns a result. The calling script includes an application file at the top via require_once. This application file includes my session, database connection, function, and other often needed scripts using the same method, via require_once.

I call the function from inside the script and get an error because it is not able to find my dbconnection variable (I am using mysqli). The only way I have been able to get the function to work is by including the dbconnection code inside the function.

How can I access that variable and not have to include the code a second time?

//top of calling file
<?php require_once '../includes/application.php'; ?>

//contents of application file
<?php require_once("../includes/sessions.php"); ?>
<?php require_once("../includes/dbconnect.php"); ?>
<?php require_once("../includes/functions.php"); ?>
<?php require_once("../includes/validation_functions.php"); ?>
<?php require_once("../includes/breadcrumb.php"); ?>

//contents of dbconnect file
<?php
  // Create a database connection
  $dbhost = "";
  // $dbuser = "";
  // $dbpass = "";
  $dbuser = "";
  $dbpass = "";
  $dbname = "";
  $db = mysqli_connect($dbhost, $dbuser, $dbpass, $dbname);
  // Test if connection occurred.
  if(mysqli_connect_errno()) {
    die("Database connection failed: " . 
         mysqli_connect_error() . 
         " (" . mysqli_connect_errno() . ")"
    );
  }
?>

//function call from within the calling file
<?php
 $crewresult = getCrewDescription($li["CrewId"]);
 echo "Code: " .  $crewresult['CrewCode'] . "Description: " . $crewresult['CrewDescription']; 
?>

//finally the function itself
<?php
	function getCrewDescription($CrewID) {

		$querystring =  " SELECT yadda";
		$querystring .= " FROM yidda";
		$querystring .= " WHERE yackity = ";
		$querystring .= (int) schmackity;
		
		$result_get_crew = mysqli_query($thisdb, $querystring);

		if(!$result_get_crew) {
			die("Database error in function getCrewDescription.");
		}
		if(mysqli_num_rows($result_get_crew)) {
			while ($record = mysqli_fetch_assoc($result_get_crew)) {
				$aarray_crew = array("CrewCode" => $record['CrewCode'], "CrewDescription" => $record['LongDescription']);
			}
		} else {
				$aarray_crew = array("CrewCode" => 0, "CrewDescription" => "No Crew Found");
		}	
		mysqli_free_result($result_get_crew);
		return $aarray_crew;
	}
?>

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Question by:medievalman
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LVL 82

Accepted Solution

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Dave Baldwin earned 500 total points
Comment Utility
You have to make the connection variable a 'global' in each routine or function that uses it.  Also... everything between the PHP close and open tags will be sent to the browser if this is for a web page including what you think are comments.  '//' only works for comments Inside the PHP tags.

I just edited the top section although I didn't see anything in your code that wouldn't work between a single open and close tag.  If you use anything that requires headers or cookies to be sent, those extra characters will cause it to fail.
<?php //top of calling file
require_once '../includes/application.php';

//contents of application file
require_once("../includes/sessions.php");
require_once("../includes/dbconnect.php");
php require_once("../includes/functions.php");
require_once("../includes/validation_functions.php");
require_once("../includes/breadcrumb.php"); ?>

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Expert Comment

by:Ray Paseur
Comment Utility
Without dragging this into a really long question and answer session, you may not get the best answer and the answer you need for application development.  So rather than trying to answer, I'll just leave this here as encouragement for your future learning.  It's not simple at first, but it transforms your software development process from one that can only survive in isolation to one that can be shared with your colleagues and proved to be testable, dependable and reliably error free.

Learn about Dependency Injection.  Using PHP require_once() gives you dependencies that are impossible to mock or test.  Same thing with the global keyword.  Injecting the dependencies (like the database connection and the function definitions) enables you to mock these dependencies, causing the mock objects to return predictable and testable values.

http://en.wikipedia.org/wiki/Dependency_injection
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Author Comment

by:medievalman
Comment Utility
Thank you, Dave. Declaring global $db in the function did the trick. The comments in the code section of my post were merely for guidance as to what code was where.
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Expert Comment

by:Dave Baldwin
Comment Utility
You're welcome, glad to help.
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