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. See utf8_encode()
and utf8_decode() for some Unicode support.
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.
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 will also 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 and escape sequences
for special characters will not be expanded
when they occur in single quoted strings.
<?php echo 'this is a simple string';
echo 'You can also have embedded newlines in strings this way as it is okay to do';
// Outputs: Arnold once said: "I'll be back" echo 'Arnold once said: "I\'ll be back"';
// Outputs: You deleted C:\*.*? echo 'You deleted C:\\*.*?';
// Outputs: You deleted C:\*.*? echo 'You deleted C:\*.*?';
// Outputs: This will not expand: \n a newline echo 'This will not expand: \n a newline';
// Outputs: Variables do not $expand $either echo 'Variables do not $expand $either'; ?>
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.
It's also important to realize that the first character before
the closing identifier must be a newline as defined by your
operating system. This is \r on Macintosh
for example. Closing delimiter (possibly followed by a semicolon) must
be followed by a newline too.
If this rule is broken and the closing identifier is not "clean"
then it's not considered to be a closing identifier and PHP
will continue looking for one. If in this case a proper closing
identifier is not found then a parse error will result with the
line number being at the end of the script.
It is not allowed to use heredoc syntax in initializing class members.
Use other string syntaxes instead.
Example 11-3. Invalid example
<?php class foo { public $bar = <<<EOT bar EOT; } ?>
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 heredoc as with
strings.
Example 11-4. 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 $bar;
When a string is specified in double quotes or with
heredoc, variables are
parsed within it.
There are two types of syntax: a
simple
one and a
complex
one.
The simple syntax is the most common and convenient. It provides a way
to parse a variable, an array value, or an
object property.
The complex syntax was introduced in PHP 4, and can be recognised
by the curly braces surrounding the expression.
If a dollar sign ($) is encountered, the
parser will greedily take as many 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.
<?php $beer = 'Heineken'; echo "$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 ${beer}s"; // works echo "He drank some {$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.
<?php // These examples are specific to using arrays inside of strings. // When outside of a string, always quote your array string keys // and do not use {braces} when outside of strings either.
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 "{\$" to get a literal "{$").
Some examples to make it clear:
<?php // Let's show all errors error_reporting(E_ALL);
$great = 'fantastic';
// Won't work, outputs: This is { fantastic} echo "This is { $great}";
// Works, outputs: This is fantastic echo "This is {$great}"; echo "This is ${great}";
// Works echo "This square is {$square->width}00 centimeters broad.";
// Works echo "This works: {$arr[4][3]}";
// This is wrong for the same reason as $foo[bar] is wrong // outside a string. In other words, it will still work but // because PHP first looks for a constant named foo, it will // throw an error of level E_NOTICE (undefined constant). echo "This is wrong: {$arr[foo][3]}";
// Works. When using multi-dimensional arrays, always use // braces around arrays when inside of strings echo "This works: {$arr['foo'][3]}";
// Works. echo "This works: " . $arr['foo'][3];
echo "You can even write {$obj->values[3]->name}";
echo "This is the value of the var named $name: {${$name}}"; ?>
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.
You can convert a value to a string using the (string)
cast, or the strval() function. String conversion
is automatically done in the scope of an expression for you where a
string is needed. This happens when you use the echo()
or print() functions, or when you compare a variable
value to a string. Reading the manual sections on Types and Type Juggling will make
the following clearer. See also settype().
A booleanTRUE value is converted to the string "1",
the FALSE value is represented as "" (empty string).
This way you can convert back and forth between boolean and string values.
An integer or a floating point number (float)
is converted to a string representing the number with its digits
(including the exponent part for floating point numbers).
Arrays are always converted to the string "Array",
so you cannot dump out the contents of an array with
echo() or print() to see what is inside
them. To view one element, you'd do something like
echo $arr['foo']. See below for tips on dumping/viewing the
entire contents.
Objects are always converted to the string "Object".
If you would like to print out the member variable values of an
object for debugging reasons, read the paragraphs
below. If you would like to find out the class name of which an object
is an instance of, use get_class().
As of PHP 5, __toString() method is used if applicable.
Resources are always converted to strings with the structure
"Resource id #1" where 1 is
the unique number of the resource assigned by PHP during runtime.
If you would like to get the type of the resource, use
get_resource_type().
NULL is always converted to an empty string.
As you can see above, printing out the arrays, objects or resources does not
provide you any useful information about the values themselves. Look at the
functions print_r() and var_dump()
for better ways to print out values for debugging.
You can also convert PHP values to strings to store them permanently. This
method is called serialization, and can be done with the function
serialize(). You can also serialize PHP values to
XML structures, if you have WDDX support
in your PHP setup.
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.
<?php $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; // $foo is float (11) ?>
For more information on this conversion, see the Unix manual page
for strtod(3).
If you would like to test any of the examples in this section,
you can cut and paste the examples and insert the following line
to see for yourself what's going on:
<?php echo "\$foo==$foo; type is " . gettype ($foo) . "<br />\n"; ?>
Do not expect to get the code of one character by converting it
to integer (as you would do in C for example). Use the functions
ord() and chr() to convert
between charcodes and characters.
