Strings in PHP

By: Andi, Stig and Derick in PHP Tutorials on 2008-11-21

Strings in PHP are a sequence of characters that are always internally nullterminated. However, unlike some other languages, such as C, PHP does not rely on the terminating null to calculate a string's length, but remembers its length internally. This allows for easy handling of binary data in PHP - for example, creating an image on-the-fly and outputting it to the browser. The maximum length of strings varies according to the platform and C compiler, but you can expect it to support at least 2GB. Don't write programs that test this limit because you're likely to first reach your memory limit.

When writing string values in your source code, you can use double quotes ("), single quotes (') or here-docs to delimit them. Each method is explained in this tutorial..

Double Quotes: Examples for double quotes:

"PHP: Hypertext Pre-processor"

"GET / HTTP/1.0\n"

"1234567890"

Strings can contain pretty much all characters. Some characters can't be written as is, however, and require special notation: An additional feature of double-quoted strings is that certain notations of variables and expressions can be embedded directly within them. Without going into specifics, here are some examples of legal strings that embed variables. The references to variables are automatically replaced with the variables" values, and if the values aren't strings, they are converted to their corresponding string representations (for example, the integer 123 would be first converted to the string "123").

"The result is $result\n"

"The array offset $i contains $arr[$i]"

In cases, where you"d like to concatenate strings with values (such as variables and expressions) and this syntax isn't sufficient, you can use the . (dot) operator to concatenate two or more strings. This operator is covered in a later section.

Single Quotes: In addition to double quotes, single quotes may also delimit strings. However, in contrast to double quotes, single quotes do not support all the double quotes" escaping and variable substitution.

The following table includes the only two escapings supported by single quotes:

\n	Newline.
\t	Tab.
\"	Double quote.
\\	Backslash.
\0	ASCII 0 (null).
\r	Line feed.
\$	Escape $ sign so that it is not treated as a variable but as the character $.
\{Octal #}	The character represented by the specified octal #-for example,\70 represents the letter 8.
\x{Hexadecimal #}	The character represented by the specified hexadecimal #-for example, \0x32 represents the letter 2.
\'	Single quote.
\\	Backslash, used when wanting to represent a backslash followed by a single quote