PHP Strings Taking Strings Apart

PHP Strings

Taking Strings Apart

Problem

You need to break a string into pieces. For example, you want to access each line that a user enters in a <textarea> form field.

Solution

Use explode() if what separates the pieces is a constant string:

             $words = explode(' ','My sentence is not very complicated');

Use preg_split() if you need a Perl-compatible regular expression to describe the separator:

             $words = preg_split('/\d\. /','my day: 1. get up 2. get dressed 3. eat toast');
             $lines = preg_split('/[\n\r]+/',$_POST['textarea']);

Use the /i flag to preg_split() for case-insensitive separator matching:

             $words = preg_split('/ x /i','31 inches x 22 inches X 9 inches');

Discussion

The simplest solution of the bunch is explode(). Pass it your separator string, the string to be separated, and an optional limit on how many elements should be returned:

              $dwarves = 'dopey,sleepy,happy,grumpy,sneezy,bashful,doc';
              $dwarf_array = explode(',',$dwarves);

This makes $dwarf_array a seven-element array, so print_r($dwarf_array) prints:

              Array
              (
                      [0] => dopey
                      [1] => sleepy
                      [2] => happy
                      [3] => grumpy
                      [4] => sneezy
                      [5] => bashful
                      [6] => doc
              )

If the specified limit is less than the number of possible chunks, the last chunk contains the remainder:

              $dwarf_array = explode(',',$dwarves,5);
print_r($dwarf_array);

This prints:

               Array
               (
                      [0] => dopey
                      [1] => sleepy
                      [2] => happy
                      [3] => grumpy
                      [4] => sneezy,bashful,doc
                )

The separator is treated literally by explode(). If you specify a comma and a space as a separator, it breaks the string only on a comma followed by a space, not on a comma or a space.

With preg_split(), you have more flexibility. Instead of a string literal as a separator, it uses a Perl-compatible regular expression engine. 

With preg_split(), you can take advantage of various Perl-ish regular expression extensions, as well as tricks such as including the separator text in the returned array of strings:

                $math = "3 + 2 / 7 - 9";
                $stack = preg_split('/ *([+\-\/*]) */',$math,-1,PREG_SPLIT_DELIM_CAPTURE);
                print_r($stack);

This prints:

                Array
                (
                       [0] => 3
                       [1] => +
                       [2] => 2
                       [3] => /
                       [4] => 7
                       [5] => -
                       [6] => 9
                )

The separator regular expression looks for the four mathematical operators (+, -, /, *), surrounded by optional leading or trailing spaces.

The PREG_SPLIT_DELIM_CAPTURE flag tells preg_split() to include the matches as part of the separator regular expression in parentheses in the returned array of strings.

Only the mathematical operator characterclass is in parentheses, so the returned array doesn’t have any spaces in it.