I don't understand this browser detection code.

[silverglade]

Hi, I came across this code that detects a user's browser and I don't understand parts of it. Here is the code below.

 

 $agent = $_SERVER['HTTP_USER_AGENT'];

if ( strpos(strtoupper($agent), 'MSIE')) {
print "Internet Explorer";
}
else if (strpos(strtoupper($agent), 'FIREFOX')) {
print "Firefox";
}
else if (strpos(strtoupper($agent), 'KONQUEROR')) {
print "Konqueror";
}
else if (strpos(strtoupper($agent), "LYNX")) {
print "Lynx";
}
else {
print $agent;
}

 

and here is the part I don't understand.

 

if ( strpos(strtoupper($agent), 'MSIE'))

 

I know that strtoupper makes all letters uppercase,

and that strpos returns the position of the string within

the larger string, but I don't know why they are in an if

statement.  Any help or explanation is greatly appreciated. Thanks. Derek

[schilly]

if strpos finds a match it will return the position of the first character which most of the time is > 0 ie. true

 

if any of the browser agents are at the start of the string the if statement will fail falsely.

 

i beleive in order to do that properly you need to do

 

if ( strpos(strtoupper($agent), 'MSIE') !== 0) {

 

to properly look for boolean false instead of zero/false.

 

Hope this makes sense.

[Alex]

I think you mean:

 

if ( strpos(strtoupper($agent), 'MSIE') !== false) {

[btherl]

The issue with strpos() returning 0 will only affect lynx, as the other browsers start their user agent with Mozilla, and have the real identifying info later.

 

silverglade, in php any number like 1, 2, 3 is considered as "true" for an "if".  So if strpos returns the position of a string, the "if" will succeed.  If strpos doesn't find the string then it returns false, which of course makes the "if" fail.  Is that the bit you were unsure of?

[schilly]

I think you mean:

 

if ( strpos(strtoupper($agent), 'MSIE') !== false) {

bah. thx. =)

[silverglade]

Ok thank you, now I understand why they used strpos. Now I don't understand why they used strtoupper though. lol. any more help greatly appreciated. thanks. sorry.

 

<?php if ( strpos(strtoupper($agent), 'MSIE'))?>

 

I don't know why they had to capitalize the result.

[btherl]

They used strtoupper() so they can match the string in any case.  You can use strtolower() the same way.  Eg

 

strtoupper('Lynx') == 'LYNX';
strtoupper('LyNX') == 'LYNX';
strtoupper('konqueror') == 'KONQUEROR';

 

So regardless of whether the string is upper or lowercase at the start, the strtoupper() makes sure it matches.

[silverglade]

awesome thanks very much for your time. I finally understand it. Thank you and everyone. Derek :D