PHP

There is little syntactical difference between MySQL 4 and MySQL 5, but sometimes finding that difference can pinpoint a bug. The mysql_get_server_info() function will tell you what version of MySQL you are using. You can call it with no parameters, in which case it picks the most recently created MySQL resource, or with the resource handle created with mysql_connect().

Here is an example of how to use it.

$link = mysql_connect('localhost', 'mysql_user', 'mysql_password');
echo mysql_get_server_info();

You can achieve the same effect with a simple MySQL query.

$link = mysql_connect('localhost', 'mysql_user', 'mysql_password');
$query = mysql_query('SELECT VERSION() as mysql_version');

Sending multiple arguments to a function can be done using a parameter string. This is just like a URL that has data encoded into it. For example, if you wanted to send two parameters (called parameter1 and parameter2) to a function then you would use the following string.

parameter1=value1&parameter2=value2

To use this in the function you create the function as normal with a single parameter. This single parameter is the string that will contain all of your arguments.

function test($arguments)
{
}

You must run the parse_str() function on the arguments parameter to extract the data you need. You can then call the parameters by their names as variables.

If you want to know the length of a string in PHP you would normally turn to the strlen() function which simply tells you the length of the string.

$string = 'this is a string';
$strLength = strlen($string);

To use this to check the length of the string use the following example.

$string = 'this is a string';
if (strlen($string) < 20) {
 // code here
}

A quicker way of looking at the length of a string would be to use the isset() function in conjunction with the curly braces {} used for locating character from a string.

$string = 'this is a string';
if (!isset($string{20})) {
 // string too short
}

Because isset() is a language construct it works quicker than strlen() so this comparison has almost no overhead at all.

I have previously talked about the filter functions available in PHP5, but failed to spot this limitation when I was doing the research for those articles. It appears that the filter to validate URL string, namely FILTER_VALIDATE_URL, is not really adequate to the task.

Take the following examples of the filter in an if statement.

if ( filter_var($url,FILTER_VALIDATE_URL) ) {
 return true;
}else{
 return false;
};

This will return true if the URL is valid and false if the URL is invalid. To test this I plugged the following URL strings into the function and recorded each of the outcomes.

One thing that comes in useful when linking to other websites is to use a little thumbnail of the site as part of the link. Although it is possible to do this it usually involves having command line access to the server so that you can install various different programs and extensions.

The simplest mechanism accomplish this is to use third party sites to create the thumbnail for you. Here are a few examples of free thumbnail services.

www.thumbshots.org

Thumbshots provides access to small images (thumbnail size) of many different websites. However, they are very small, with no way to change this, and can often be weeks out of date if the site has had a redesign. You can access Thumbshots from any webpage by using an image with a source that reads from the Thumbshots website.

Many situations arise where you need to either insert or update some data in a table but which you will not be certain as to which function to perform. A common solution is to do a query on the table first to see if the data exists and then insert if it doesn't and update if it does. However, this creates an unnecessary overhead in that every time the code is run at least 2 queries are run.

A better way is to try to update the table and then use the mysql_info() function to detect how many rows where updated in the query and how many rows matched the parameters in the update query.

Take the following query.

UPDATE table SET value = "value" WHERE valueId = 2;

When run on a table the mysql_info() function returns the following result.

Pinpointing where an error in a program is occurring is not always easy. This can be even more of a problem when you write an SQL query that produces an error. Take the following select statement, which is clearly wrong.

ELECT * FROM table;

I tend to do this at least every now and then, and don't usually spot it until it's too late. So when I then run mysql_query() on this statement nothing happens. As far as I can tell form the code the table contains no data.

To get the error message that is produced from the SQL you can use the mysql_error() function to return the error message. The single optional parameter is the resource identifier for the MySQL connection, but if you leave this out then PHP will use the latest resource created.

echo mysql_error();

This will print the following line in your PHP output.

To create a simple HTML check box use the following bit of code.

<input type="checkbox" name="option2" value="Milk" />

To set the checkbox as filled in include a checked attribute. To make the control XHTML compliant you will need to do the following.

<input type="checkbox" name="option2" value="Milk" checked="checked" />

When the form is posted this value is sent to PHP with the $_POST superglobal array.

To link several checkboxes together to make them into an array in the PHP $_POST array you need to make all of the checkboxes have the same name, and each name must end in "[]".

Setting up a 404 page on your site will help users when they navigate to a page that doesn't exist. Rather than dropping them into a scary server message you can give them a nice friendly error page. The first step is to make sure that if the user generates a 404 error they are given a nice page. Add this line to your .htaccess file.

ErrorDocument 404 404.html

Now when a user hits a non existent page they will see you nice error page. However, you sometimes will want to produce a 404 page when the server doesn't give out a 404 error, for example, if you have the following URL.

There are many ways to sort an array in PHP, the easiest being to use the sort() function built into PHP. This sort function is quick but has it's limitations, especially when sorting things like dates as PHP usually guesses which value is higher than the other and can produce odd results. However, there are plenty of sorting algorithms available than can allow you to sort an array in any way you want.

The simplest of these is called the bubble sort. Here is a function that will sort an array of values using the bubble sort algorithm.