Could someone break this down

Egri

I'm reading the programing manual on www.php.net and I ran into something that I don't really understand.

The code is this

<?php
$mystring = 'abc';
$findme  = 'a';
$pos = strpos($mystring, $findme);

// Note our use of ===.  Simply == would not work as expected
// because the position of 'a' was the 0th (first) character.
if ($pos === false) {
   echo "The string '$findme' was not found in the string '$mystring'";
} else {
   echo "The string '$findme' was found in the string '$mystring'";
   echo " and exists at position $pos";
}

// We can search for the character, ignoring anything before the offset
$newstring = 'abcdef abcdef';
$pos = strpos($newstring, 'a', 1); // $pos = 7, not 0
?>

What I can't figure out is why do you have to use "===". I'm actually having a hard time understanding why you would have to use "==" if it did work.

Another example is

<?php
if (strpos($_SERVER['HTTP_USER_AGENT'], 'MSIE') !== FALSE) {
   echo 'You are using Internet Explorer.<br />';
}
?>

Now I understand what its doing here. Basically strpos() is looking inside of "$_SERVER['HTTP_USER_AGENT']" for 'MSIE'.

I understand that part what I don't understand is why the !== FALSE is there. I know that != means Does not Equal, but why the second =?

Can anyone help me out?

laserlight

strpos() returns a value in the range [0,n-1], where n is the string length.
However, if the substring is not found, strpos() returns false.

Now, if == was used, then 0 being a false value, would make it appear that the substring was not found even if the substring was at the start of the string.
Using === means that type checking is performed, and since 0 is an integer, it is not equalent to a literal false.

Egri

Originally posted by laserlight
strpos() returns a value in the range [0,n-1], where n is the string length.
However, if the substring is not found, strpos() returns false.

Now, if == was used, then 0 being a false value, would make it appear that the substring was not found even if the substring was at the start of the string.
Using === means that type checking is performed, and since 0 is an integer, it is not equalent to a literal false.

So if I had something like

$_test = 'abc def ghi'

strpos($_test, 'g')

basically strpos() takes out all the spaces, so 'g' would be #7 vice #9

So == "skips" the first part? and === reads the whole line?

$pos = strpos(abc, a);
if ($pos == false)

then the 'a' does not exist? but if I used

$pos = strpos(abc, a);
if ($pos === false)

then the 'a' would exist?

laserlight

No, the first character of a string is at position 0.

($a == $b) tests if $a is equal to $b
($a === $b) tests if $a is equal to $b and of the same type

Egri

Originally posted by laserlight
No, the first character of a string is at position 0.

($a == $b) tests if $a is equal to $b
($a === $b) tests if $a is equal to $b and of the same type

ok that makes sense, but how do you know when to use one from the other?

Egri

Originally posted by Egri
ok that makes sense, but how do you know when to use one from the other?

Ahhhhhh, the light bulb just clicked on.

if I had

<?php 
$mystring = 'abc'; 
$findme  = 'a'; 
$pos = strpos($mystring, $findme);

if I used:

if ($pos == false)
then it would be false because 'a' doesn't eqaul 'abc'.
Basically for the '==' to work $mystring would have be 'a'

but because I'm looking for the letter 'a' inside of 'abc' I would have to use 'if ($pos === false)' because like you said. '===' "tests if $a is equals to $b and of the same type"

which basically breaks down like a "search engine" you insert what your looking for and it finds the words or letters even if it has nothing to do with what your really looking for.

Fantastic, thanks so very much for your help Laserlight!