Chapter 1. Strings [Accessing Substrings]

Chapter 1. Strings

Contents:

Introduction
Accessing Substrings
Replacing Substrings
Processing a String One Character at a Time
Reversing a String by Word or Character
Expanding and Compressing Tabs
Controlling Case
Interpolating Functions and Expressions Within Strings
Trimming Blanks from a String
Parsing Comma-Separated Data
Parsing Fixed-Width Delimited Data
Taking Strings Apart
Wrapping Text at a Certain Line Length
Storing Binary Data in Strings

1.2. Accessing Substrings

You want to extract part of a string, starting at a particular place in the string. For example, you want the first eight characters of a username entered into a form.

1.2.1. Solution

Use substr( ) to select your substrings:

$substring = substr($string,$start,$length);
$username = substr($_REQUEST['username'],0,8);

1.2.2. Discussion

If $start and $length are positive, substr( ) returns $length characters in the string, starting at $start. The first character in the string is at position 0:

print substr('watch out for that tree',6,5);
out f

If you leave out $length, substr( ) returns the string from $start to the end of the original string:

print substr('watch out for that tree',17);
t tree

If $start plus $length goes past the end of the string, substr( ) returns all of the string from $start forward:

print substr('watch out for that tree',20,5);
ree

If $start is negative, substr( ) counts back from the end of the string to determine where your substring starts:

print substr('watch out for that tree',-6);
print substr('watch out for that tree',-17,5);
t tree
out f

If $length is negative, substr( ) counts back from the end of the string to determine where your substring ends:

print substr('watch out for that tree',15,-2);
print substr('watch out for that tree',-4,-1);
hat tr
tre

1.2.3. See Also

Documentation on substr( ) at http://www.php.net/substr.