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# Strings

A string is series of characters. In PHP, a character is the same as a byte, that is, there are exactly 256 different characters possible. This also implies that PHP has no native support of Unicode.

> Note: It is no problem for a string to become very large. There is no practical bound to the size of strings imposed by PHP, so there is no reason at all to worry about long strings.

## Syntax

A string literal can be specified in three different ways.

- single quoted

- double quoted

- heredoc syntax

### Single quoted

The easiest way to specify a simple string is to enclose it in single quotes (the character `'`).

To specify a literal single quote, you will need to escape it with a backslash (`\`), like in many other languages. If a backslash needs to occur before a single quote or at the end of the string, you need to double it. Note that if you try to escape any other character, the backslash too will be printed! So usually there is no need to escape the backslash itself.

> Note: In PHP 3, a warning will be issued at the `E_NOTICE` level when this happens.

> Note: Unlike the two other syntaxes, variables will not be expanded when they occur in single quoted strings.

    echo 'this is a simple string';
    echo 'You can also have embedded newlines in strings,
    like this way.';
    echo 'Arnold once said: "I\'ll be back"';
    // output: ... "I'll be back"
    echo 'Are you sure you want to delete C:\\*.*?';
    // output: ... delete C:\*.*?
    echo 'Are you sure you want to delete C:\*.*?';
    // output: ... delete C:\*.*?
    echo 'I am trying to include at this point: \n a newline';
    // output: ... this point: \n a newline

### Double quoted

If the string is enclosed in double-quotes ("), PHP understands more escape sequences for special characters:

Table 7-1. Escaped characters

sequence | meaning
--- | ---
`\n` | linefeed (LF or 0x0A (10) in ASCII)
`\r` | carriage return (CR or 0x0D (13) in ASCII)
`\t` | horizontal tab (HT or 0x09 (9) in ASCII)
`\\` | backslash
`\$` | dollar sign
`\"` | double-quote
`\[0-7]{1,3}` | the sequence of characters matching the regular expression is a character in octal notation
`\x[0-9A-Fa-f]{1,2}` | the sequence of characters matching the regular expression is a character in hexadecimal notation

Again, if you try to escape any other character, the backslash will be printed too!

But the most important pre of double-quoted strings is the fact that variable names will be expanded. See string parsing for details.

### Heredoc

Another way to delimit strings is by using heredoc syntax ("<<<"). One should provide an identifier after `<<<`, then the string, and then the same identifier to close the quotation.

The closing identifier must begin in the first column of the line. Also, the identifier used must follow the same naming rules as any other label in PHP: it must contain only alphanumeric characters and underscores, and must start with a non-digit character or underscore.

Warning
It is very important to note that the line with the closing identifier contains no other characters, except possibly a semicolon (`;`). That means especially that the identifier may not be indented, and there may not be any spaces or tabs after or before the semicolon.

Heredoc text behaves just like a double-quoted string, without the double-quotes. This means that you do not need to escape quotes in your here docs, but you can still use the escape codes listed above. Variables are expanded, but the same care must be taken when expressing complex variables inside a here doc as with strings.

Example 7-2. Heredoc string quoting example
    <?php
    $str = <<<EOD
    Example of string
    spanning multiple lines
    using heredoc syntax.
    EOD;

    /* More complex example, with variables. */
    class foo
    {
        var $foo;
        var $bar;

        function foo()
        {
            $this->foo = 'Foo';
            $this->bar = array('Bar1', 'Bar2', 'Bar3');
        }
    }

    $foo = new foo();
    $name = 'MyName';

    echo <<<EOT
    My name is "$name". I am printing some $foo->foo.
    Now, I am printing some {$foo->bar[1]}.
    This should print a capital 'A': \x41
    EOT;
    ?>

> Note: Heredoc support was added in PHP 4.

### Variable parsing

When a string is specified in double quotes or with heredoc, variables are parsed within it.

There are two types of syntax, a simple one and a complex one. The simple syntax is the most common and convenient, it provides a way to parse a variable, an array value, or an object property.

The complex syntax was introduced in PHP 4, and can be recognised by the curly braces surrounding the expression.

#### Simple syntax

If a dollar sign (`$`) is encountered, the parser will greedily take as much tokens as possible to form a valid variable name. Enclose the variable name in curly braces if you want to explicitly specify the end of the name.

    $beer = 'Heineken';
    echo "$beer's taste is great"; // works, "'" is an invalid character for varnames
    echo "He drank some $beers"; // won't work, 's' is a valid character for varnames
    echo "He drank some ${beer}s"; // works

Similarly, you can also have an array index or an object property parsed. With array indices, the closing square bracket (`]`) marks the end of the index. For object properties the same rules apply as to simple variables, though with object properties there doesn't exist a trick like the one with variables.

    $fruits = array( 'strawberry' => 'red' , 'banana' => 'yellow' );

    // note that this works differently outside string-quotes.
    echo "A banana is $fruits[banana].";

    echo "This square is $square->width meters broad.";

    // Won't work. For a solution, see the complex syntax.
    echo "This square is $square->width00 centimeters broad.";

For anything more complex, you should use the complex syntax.

#### Complex (curly) syntax

This isn't called complex because the syntax is complex, but because you can include complex expressions this way.

In fact, you can include any value that is in the namespace in strings with this syntax. You simply write the expression the same way as you would outside the string, and then include it in { and }. Since you can't escape '{', this syntax will only be recognised when the $ is immediately following the {. (Use "{\$" or "\{$" to get a literal "{$"). Some examples to make it clear:

    $great = 'fantastic';
    echo "This is { $great}"; // won't work, outputs: This is { fantastic}
    echo "This is {$great}";  // works, outputs: This is fantastic
    echo "This square is {$square->width}00 centimeters broad.";
    echo "This works: {$arr[4][3]}";

    // This is wrong for the same reason
    // as $foo[bar] is wrong outside a string.
    echo "This is wrong: {$arr[foo][3]}";

    echo "You should do it this way: {$arr['foo'][3]}";
    echo "You can even write {$obj->values[3]->name}";
    echo "This is the value of the var named $name: {${$name}}";

### String access by character

Characters within strings may be accessed by specifying the zero-based offset of the desired character after the string in curly braces.

> Note: For backwards compatibility, you can still use the array-braces. However, this syntax is deprecated as of PHP 4.

Example 7-3. Some string examples
    <?php
    /* Assigning a string. */
    $str = "This is a string";

    /* Appending to it. */
    $str = $str . " with some more text";

    /* Another way to append, includes an escaped newline. */
    $str .= " and a newline at the end.\n";

    /* This string will end up being '<p>Number: 9</p>' */
    $num = 9;
    $str = "<p>Number: $num</p>";

    /* This one will be '<p>Number: $num</p>' */
    $num = 9;
    $str = '<p>Number: $num</p>';

    /* Get the first character of a string  */
    $str = 'This is a test.';
    $first = $str{0};

    /* Get the last character of a string. */
    $str = 'This is still a test.';
    $last = $str{strlen($str)-1};
    ?>

## Useful functions

Strings may be concatenated using the '.' (dot) operator. Note that the '+' (addition) operator will not work for this. Please see String operators for more information.

There are a lot of useful functions for string modification.

See the string functions section for general functions, the regular expression functions for advanced find&replacing (in two tastes: Perl and POSIX extended).

There are also functions for URL-strings, and functions to encrypt/decrypt strings (mcrypt and mhash).

Finally, if you still didn't find what you're looking for, see also the character type functions.

## String conversion

When a string is evaluated as a numeric value, the resulting value and type are determined as follows.

The string will evaluate as a float if it contains any of the characters '.', 'e', or 'E'. Otherwise, it will evaluate as an integer.

The value is given by the initial portion of the string. If the string starts with valid numeric data, this will be the value used. Otherwise, the value will be 0 (zero). Valid numeric data is an optional sign, followed by one or more digits (optionally containing a decimal point), followed by an optional exponent. The exponent is an 'e' or 'E' followed by one or more digits.

    $foo = 1 + "10.5";              // $foo is float (11.5)
    $foo = 1 + "-1.3e3";            // $foo is float (-1299)
    $foo = 1 + "bob-1.3e3";         // $foo is integer (1)
    $foo = 1 + "bob3";              // $foo is integer (1)
    $foo = 1 + "10 Small Pigs";     // $foo is integer (11)
    $foo = 4 + "10.2 Little Piggies"; // $foo is float (14.2)
    $foo = "10.0 pigs " + 1;        // $foo is float (11)
    $foo = "10.0 pigs " + 1.0;      // $foo is float (11)

For more information on this conversion, see the Unix manual page for strtod(3).

If you would like to test any of the examples in this section, you can cut and paste the examples and insert the following line to see for yourself what's going on:

    echo "\$foo==$foo; type is " . gettype ($foo) . "<br />\n";

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