Month: January 2011

Categories
MySQL PHP

PHP isset() function returns FALSE even though the variable is defined

Let’s say we have a table item in a MySQL database, with the primary key iditem and a field code that can be NULL:

CREATE TABLE `item` (
`iditem` int(10) unsigned NOT NULL,
`code` VARCHAR(10) DEFAULT NULL,
PRIMARY KEY (`iditem`),
);

--
-- Dumping data for table `item`
--

INSERT INTO `item` (`iditem`, `code`) VALUES
(1, 'as1435v'),
(2, NULL),
(3, 1, 'YHryt4t90');

In PHP we define a variable $item_code that we initialize with 0 and then we run a query for setting the value of $item_code to the code of the item which has the id 2 in our database:

$item_code = 0;
$query = "SELECT code FROM item WHERE iditem = 2";
$result = mysql_query($conn); //$conn is our database connection
if($result) {
	if($row = mysql_fetch_row($result)) {
		$item_code = $row[0];
	}
}

if(isset($item_code)) {
	echo "item code: ".$item_code;
} else {
	echo "item code is not set";
}

The output will be:
item code is not set

That is because the code is NULL in the database and it is transferred into PHP not as the empty string, but as NULL.
And the name of the isset() function is misleading as it returns FALSE not only when a variable is not defined, but also when a variable has been set to NULL.

Categories
HTML PHP

Strange empty text line appearing inside my page

Usually you see an empty text line and you look at the source and you see nothing there just a space…

That happens often when the files that are outputted are using the encoding UTF8 with signature, instead of using the correct encoding UTF8 without signature.

Categories
JavaScript

Delayed javascript function/handler gets the right variable/parameter values

So we have a function that adds a handler function that is called after an ajax load or at a later time and we need to execute the handler function code for each item inside an array allowing the function to access the array values. Usually with the simplest try you would get some code that get’s executed with invalid variable values. Examples are below.

The wrong code:

//the function that will do the stuff for each array
var dostuff = function (arr) {
var n = arr.length,
    i;
    for(i = 0; i < n; i++) {
        var o = arr[i];
        //event bind or delayed function call
        setTimeout(function () {
                //we want to access here the correct arr[i]
                //when the code gets here the value of o is arr[arr.length-1]
                console.log(o);
        }, 1000);
    }
}
dostuff([1,2,3,4]);

You can load the code into your javascript console to see it in action.
The output appears after 1 second and it is like this:

4
4
4
4

I don't need that. I need something that works so we need to wrap the handler call into a function call that will pass the current values as parameters.

var dostuff = function (arr) {
var n = arr.length,
    i;
    for(i = 0; i < n; i++) {
        var o = arr[i];
        (function (y) {
            setTimeout(function () {
                console.log(y);
            }, 1000);
        }) (o);
    }
}
dostuff([1,2,3,4]);

The output appears after 1 second and it is like this:

1
2
3
4

The final best solution would be to have the function inside for already defined so you don't define it on every loop:

var dostuff_item = function (y) {
            setTimeout(function () {
                console.log(y);
         }, 1000);
 }
var dostuff = function (arr) {
var n = arr.length,
    i;
    for(i = 0; i < n; i++) {
        var o = arr[i];
        dostuff_item (o);
    }
}
dostuff([1,2,3,4]);

Tada!