Tag Archives: Tutorial

PHP: isset () vs strlen ()

How to test the length of a string in PHP ?  Well, PHP has a function called strlen () for this purpose.
So obviously, a simple if (strlen ($str) > 10) { ... } should do the trick, isn’t it?

Actually, there’s another way to do that: considering that a string is an array of characters, it’s possible to test if a character is set at the length we want to check with isset (). So the line of code above should be replace by if (isset ($str [10]) { ... }.

Why should we use isset () instead of strlen ()?

Well, it’s way faster: running the test above 100 000 times for each function gives me:
strlen () : 0.034812927246094 seconds
isset () : 0.0079290866851807 seconds

Getting current datetime in ISO format in MySQL

Here is the MySQL function to use to get the current datetime as ISO 8601 format as asked in DarwinCore:

DATE_FORMAT(NOW(),'%Y-%m-%dT%TZ')

DATE_FORMAT() is obviously a function for formatting date and time, and we are using here %Y for four-digit year, %m for two-digits month, %d for two-digits day and %T for 24-hour time (hh:mm:ss). NOW() gives the current datetime.

And then you get a nice figure like this one:

2009-06-10T07:43:12Z

Note that the same result can be achieved with:
CONCAT(CURDATE(),'T',CURTIME(),'Z')

Where CONCAT() is used for concatenating strings, and CURDATE() and CURTIME() give respectively the current date and the current time.

UPDATE: There is now a page for getting the current datetime in different formats. Check the page here: Get the current date in different formats in MySQL.

PHP: isset()

isset() is a function testing if a variable $var is set or not.

boolean isset (mixed $var[, mixed $var[,...]])

It returns TRUE is the variable is set, and FALSE if it isn’t.

Using isset() for testing a variable saves some times compared to try to use an nonexistent one. It also helps to avoid error messages from PHP:

/* The line below generates the warning message:
* Notice: Undefined variable: var in /path/to/script.php on line 1
*/
$toto = $var;

/* Of course it's possible to silence with @ the warnings from PHP but it's costly */
$toto = @$var;

/* Do this instead: */
if (isset ($var)) {
$toto = $var;
}

As seen in the function definition above, isset can take multiple arguments. But it is faster to have an if statement with one isset() call per variable rather than one isset() call with several variables:

if (isset($a) && isset($b)) { } /* Fast */

if (isset($a, $b)) { } /* Slow */