Strings

A string is a series of characters, where a character is the same as a byte. This means that PHP only supports a 256-character set, and hence does not offer native Unicode support. See details of the string type.

Note: On 32-bit builds, a string can be as large as up to 2GB (2147483647 bytes maximum)

Syntax

A string literal can be specified in four different ways:

Single quoted

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

To specify a literal single quote, escape it with a backslash (\). To specify a literal backslash, double it (\\). All other instances of backslash will be treated as a literal backslash: this means that the other escape sequences you might be used to, such as \r or \n, will be output literally as specified rather than having any special meaning.

Note: Unlike the double-quoted and heredoc 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';
?>

Double quoted

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

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)
\v vertical tab (VT or 0x0B (11) in ASCII)
\e escape (ESC or 0x1B (27) in ASCII)
\f form feed (FF or 0x0C (12) 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, which silently overflows to fit in a byte (e.g. "\400" === "\000")
\x[0-9A-Fa-f]{1,2} the sequence of characters matching the regular expression is a character in hexadecimal notation
\u{[0-9A-Fa-f]+} the sequence of characters matching the regular expression is a Unicode codepoint, which will be output to the string as that codepoint's UTF-8 representation

As in single quoted strings, escaping any other character will result in the backslash being printed too.

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

Heredoc

A third way to delimit strings is the heredoc syntax: <<<. After this operator, an identifier is provided, then a newline. The string itself follows, and then the same identifier again to close the quotation.

The closing identifier may be indented by space or tab, in which case the indentation will be stripped from all lines in the doc string. Prior to PHP 7.3.0, the closing identifier must begin in the first column of the line.

Also, the closing identifier 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.

Example #1 Basic Heredoc example as of PHP 7.3.0

<?php
// no indentation
echo <<<END
a
b
c
\n
END;

// 4 spaces of indentation
echo <<<END
a
b
c
END;

Output of the above example in PHP 7.3:

      a
     b
    c

  a
 b
c

If the closing identifier is indented further than any lines of the body, then a ParseError will be thrown:

Example #2 Closing identifier must not be indented further than any lines of the body

<?php
echo <<<END
a
b
c
END;

Output of the above example in PHP 7.3:

PHP Parse error:  Invalid body indentation level (expecting an indentation level of at least 3) in example.php on line 4

If the closing identifier is indented, tabs can be used as well, however, tabs and spaces must not be intermixed regarding the indentation of the closing identifier and the indentation of the body (up to the closing identifier). In any of these cases, a ParseError will be thrown. These whitespace constraints have been included because mixing tabs and spaces for indentation is harmful to legibility.

Example #3 Different indentation for body (spaces) closing identifier

<?php
// All the following code do not work.

// different indentation for body (spaces) ending marker (tabs)
{
echo <<<END
a
END;
}

// mixing spaces and tabs in body
{
echo <<<END
a
END;
}

// mixing spaces and tabs in ending marker
{
echo <<<END
a
END;
}

Output of the above example in PHP 7.3:

PHP Parse error:  Invalid indentation - tabs and spaces cannot be mixed in example.php line 8

The closing identifier for the body string is not required to be followed by a semicolon or newline. For example, the following code is allowed as of PHP 7.3.0:

Example #4 Continuing an expression after a closing identifier

<?php
$values
= [<<<END
a
b
c
END, 'd e f'];
var_dump($values);

Output of the above example in PHP 7.3:

array(2) {
  [0] =>
  string(11) "a
  b
    c"
  [1] =>
  string(5) "d e f"
}
Warning

If the closing identifier was found at the start of a line, then regardless of whether it was a part of another word, it may be considered as the closing identifier and causes a ParseError.

Example #5 Closing identifier in body of the string tends to cause ParseError

<?php
$values
= [<<<END
a
b
END ING
END
, 'd e f'];

Output of the above example in PHP 7.3:

PHP Parse error:  syntax error, unexpected identifier "ING", expecting "]" in example.php on line 6

To avoid this problem, it is safe to follow the simple rule: do not choose as a closing identifier if it appears in the body of the text.

Warning

Prior to PHP 7.3.0, it is very important to note that the line with the closing identifier must contain no other characters, except a semicolon (;). That means especially that the identifier may not be indented, and there may not be any spaces or tabs before or after the semicolon. It's also important to realize that the first character before the closing identifier must be a newline as defined by the local operating system. This is \n on UNIX systems, including macOS. The closing delimiter must also be followed by a newline.

If this rule is broken and the closing identifier is not "clean", it will not be considered a closing identifier, and PHP will continue looking for one. If a proper closing identifier is not found before the end of the current file, a parse error will result at the last line.

Example #6 Invalid example, prior to PHP 7.3.0

<?php
class foo {
public
$bar = <<<EOT
bar
EOT;
}
// Identifier must not be indented
?>

Example #7 Valid example, even if prior to PHP 7.3.0

<?php
class foo {
public
$bar = <<<EOT
bar
EOT;
}
?>

Heredocs containing variables can not be used for initializing class properties.

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

Example #8 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
__construct()
{
$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;
?>

The above example will output:

My name is "MyName". I am printing some Foo.
Now, I am printing some Bar2.
This should print a capital 'A': A

It is also possible to use the Heredoc syntax to pass data to function arguments:

Example #9 Heredoc in arguments example

<?php
var_dump
(array(<<<EOD
foobar!
EOD
));
?>

It's possible to initialize static variables and class properties/constants using the Heredoc syntax:

Example #10 Using Heredoc to initialize static values

<?php
// Static variables
function foo()
{
static
$bar = <<<LABEL
Nothing in here...
LABEL;
}

// Class properties/constants
class foo
{
const
BAR = <<<FOOBAR
Constant example
FOOBAR;

public
$baz = <<<FOOBAR
Property example
FOOBAR;
}
?>

The opening Heredoc identifier may optionally be enclosed in double quotes:

Example #11 Using double quotes in Heredoc

<?php
echo <<<"FOOBAR"
Hello World!
FOOBAR;
?>

Nowdoc

Nowdocs are to single-quoted strings what heredocs are to double-quoted strings. A nowdoc is specified similarly to a heredoc, but no parsing is done inside a nowdoc. The construct is ideal for embedding PHP code or other large blocks of text without the need for escaping. It shares some features in common with the SGML <![CDATA[ ]]> construct, in that it declares a block of text which is not for parsing.

A nowdoc is identified with the same <<< sequence used for heredocs, but the identifier which follows is enclosed in single quotes, e.g. <<<'EOT'. All the rules for heredoc identifiers also apply to nowdoc identifiers, especially those regarding the appearance of the closing identifier.

Example #12 Nowdoc string quoting example

<?php
echo <<<'EOD'
Example of string spanning multiple lines
using nowdoc syntax. Backslashes are always treated literally,
e.g. \\ and \'.
EOD;

The above example will output:

Example of string spanning multiple lines
using nowdoc syntax. Backslashes are always treated literally,
e.g. \\ and \'.

Example #13 Nowdoc string quoting example with variables

<?php
class foo
{
public
$foo;
public
$bar;

function
__construct()
{
$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 not print a capital 'A': \x41
EOT;
?>

The above example will output:

My name is "$name". I am printing some $foo->foo.
Now, I am printing some {$foo->bar[1]}.
This should not print a capital 'A': \x41

Example #14 Static data example

<?php
class foo {
public
$bar = <<<'EOT'
bar
EOT;
}
?>

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 embed a variable, an array value, or an object property in a string with a minimum of effort.

The complex syntax can be recognised by the curly braces surrounding the expression.

Simple syntax

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 to explicitly specify the end of the name.

<?php
$juice
= "apple";

echo
"He drank some $juice juice.".PHP_EOL;
// Unintended. "s" is a valid character for a variable name, so this refers to $juices, not $juice.
echo "He drank some juice made of $juices.";
// Explicitly specify the end of the variable name by enclosing the reference in braces.
echo "He drank some juice made of {$juice}s.";
?>

The above example will output:

He drank some apple juice.
He drank some juice made of .
He drank some juice made of apples.

Similarly, an array index or an object property can be parsed. With array indices, the closing square bracket (]) marks the end of the index. The same rules apply to object properties as to simple variables.

Example #15 Simple syntax example

<?php
$juices
= array("apple", "orange", "koolaid1" => "purple");

echo
"He drank some $juices[0] juice.".PHP_EOL;
echo
"He drank some $juices[1] juice.".PHP_EOL;
echo
"He drank some $juices[koolaid1] juice.".PHP_EOL;

class
people {
public
$john = "John Smith";
public
$jane = "Jane Smith";
public
$robert = "Robert Paulsen";

public
$smith = "Smith";
}

$people = new people();

echo
"$people->john drank some $juices[0] juice.".PHP_EOL;
echo
"$people->john then said hello to $people->jane.".PHP_EOL;
echo
"$people->john's wife greeted $people->robert.".PHP_EOL;
echo
"$people->robert greeted the two $people->smiths."; // Won't work
?>

The above example will output:

He drank some apple juice.
He drank some orange juice.
He drank some purple juice.
John Smith drank some apple juice.
John Smith then said hello to Jane Smith.
John Smith's wife greeted Robert Paulsen.
Robert Paulsen greeted the two .

As of PHP 7.1.0 also negative numeric indices are supported.

Example #16 Negative numeric indices

<?php
$string
= 'string';
echo
"The character at index -2 is $string[-2].", PHP_EOL;
$string[-3] = 'o';
echo
"Changing the character at index -3 to o gives $string.", PHP_EOL;
?>

The above example will output:

The character at index -2 is n.
Changing the character at index -3 to o gives strong.

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 it allows for the use of complex expressions.

Any scalar variable, array element or object property with a string representation can be included via this syntax. The expression is written the same way as it would appear outside the string, and then wrapped in { and }. Since { can not be escaped, this syntax will only be recognised when the $ immediately follows the {. Use {\$ to get a literal {$. Some examples to make it clear:

<?php
// 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}";

// Works
echo "This square is {$square->width}00 centimeters broad.";


// Works, quoted keys only work using the curly brace syntax
echo "This works: {$arr['key']}";


// Works
echo "This works: {$arr[4][3]}";

// This is wrong for the same reason as $foo[bar] is wrong outside a string.
// In other words, it will still work, but only because PHP first looks for a
// constant named foo; an error of level E_NOTICE (undefined constant) will be
// thrown.
echo "This is wrong: {$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
"This works too: {$obj->values[3]->name}";

echo
"This is the value of the var named $name: {${$name}}";

echo
"This is the value of the var named by the return value of getName(): {${getName()}}";

echo
"This is the value of the var named by the return value of \$object->getName(): {${$object->getName()}}";

// Won't work, outputs: This is the return value of getName(): {getName()}
echo "This is the return value of getName(): {getName()}";

// Won't work, outputs: C:\folder\{fantastic}.txt
echo "C:\folder\{$great}.txt"
// Works, outputs: C:\folder\fantastic.txt
echo "C:\\folder\\{$great}.txt"
?>

It is also possible to access class properties using variables within strings using this syntax.

<?php
class foo {
var
$bar = 'I am bar.';
}

$foo = new foo();
$bar = 'bar';
$baz = array('foo', 'bar', 'baz', 'quux');
echo
"{$foo->$bar}\n";
echo
"{$foo->{$baz[1]}}\n";
?>

The above example will output:

I am bar.
I am bar.

Note:

The value accessed from functions, method calls, static class variables, and class constants inside {$} will be interpreted as the name of a variable in the scope in which the string is defined. Using single curly braces ({}) will not work for accessing the return values of functions or methods or the values of class constants or static class variables.

<?php
// Show all errors.
error_reporting(E_ALL);

class
beers {
const
softdrink = 'rootbeer';
public static
$ale = 'ipa';
}

$rootbeer = 'A & W';
$ipa = 'Alexander Keith\'s';

// This works; outputs: I'd like an A & W
echo "I'd like an {${beers::softdrink}}\n";

// This works too; outputs: I'd like an Alexander Keith's
echo "I'd like an {${beers::$ale}}\n";
?>

String access and modification by character

Characters within strings may be accessed and modified by specifying the zero-based offset of the desired character after the string using square array brackets, as in $str[42]. Think of a string as an array of characters for this purpose. The functions substr() and substr_replace() can be used when you want to extract or replace more than 1 character.

Note: As of PHP 7.1.0, negative string offsets are also supported. These specify the offset from the end of the string. Formerly, negative offsets emitted E_NOTICE for reading (yielding an empty string) and E_WARNING for writing (leaving the string untouched).

Note: Prior to PHP 8.0.0, strings could also be accessed using braces, as in $str{42}, for the same purpose. This curly brace syntax was deprecated as of PHP 7.4.0 and no longer supported as of PHP 8.0.0.

Warning

Writing to an out of range offset pads the string with spaces. Non-integer types are converted to integer. Illegal offset type emits E_WARNING. Only the first character of an assigned string is used. As of PHP 7.1.0, assigning an empty string throws a fatal error. Formerly, it assigned a NULL byte.

Warning

Internally, PHP strings are byte arrays. As a result, accessing or modifying a string using array brackets is not multi-byte safe, and should only be done with strings that are in a single-byte encoding such as ISO-8859-1.

Note: As of PHP 7.1.0, applying the empty index operator on an empty string throws a fatal error. Formerly, the empty string was silently converted to an array.

Example #17 Some string examples

<?php
// Get the first character of a string
$str = 'This is a test.';
$first = $str[0];

// Get the third character of a string
$third = $str[2];

// Get the last character of a string.
$str = 'This is still a test.';
$last = $str[strlen($str)-1];

// Modify the last character of a string
$str = 'Look at the sea';
$str[strlen($str)-1] = 'e';

?>

String offsets have to either be integers or integer-like strings, otherwise a warning will be thrown.

Example #18 Example of Illegal String Offsets

<?php
$str
= 'abc';

var_dump($str['1']);
var_dump(isset($str['1']));

var_dump($str['1.0']);
var_dump(isset($str['1.0']));

var_dump($str['x']);
var_dump(isset($str['x']));

var_dump($str['1x']);
var_dump(isset($str['1x']));
?>

The above example will output:

string(1) "b"
bool(true)

Warning: Illegal string offset '1.0' in /tmp/t.php on line 7
string(1) "b"
bool(false)

Warning: Illegal string offset 'x' in /tmp/t.php on line 9
string(1) "a"
bool(false)
string(1) "b"
bool(false)

Note:

Accessing variables of other types (not including arrays or objects implementing the appropriate interfaces) using [] or {} silently returns null.

Note:

Characters within string literals can be accessed using [] or {}.

Note:

Accessing characters within string literals using the {} syntax has been deprecated in PHP 7.4. This has been removed in PHP 8.0.

Useful functions and operators

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

There are a number of useful functions for string manipulation.

See the string functions section for general functions, and the Perl-compatible regular expression functions for advanced find & replace functionality.

There are also functions for URL strings, and functions to encrypt/decrypt strings (Sodium and Hash).

Finally, see also the character type functions.

Converting to string

A value can be converted to a string using the (string) cast or the strval() function. String conversion is automatically done in the scope of an expression where a string is needed. This happens when using the echo or print functions, or when a variable is compared to a string. The sections on Types and Type Juggling will make the following clearer. See also the settype() function.

A bool true value is converted to the string "1". bool false is converted to "" (the empty string). This allows conversion back and forth between bool and string values.

An int or float is converted to a string representing the number textually (including the exponent part for floats). Floating point numbers can be converted using exponential notation (4.1E+6).

Note:

As of PHP 8.0.0, the decimal point character is always a period ("."). Prior to PHP 8.0.0, the decimal point character is defined in the script's locale (category LC_NUMERIC). See the setlocale() function.

Arrays are always converted to the string "Array"; because of this, echo and print can not by themselves show the contents of an array. To view a single element, use a construction such as echo $arr['foo']. See below for tips on viewing the entire contents.

In order to convert objects to string, the magic method __toString must be used.

Resources are always converted to strings with the structure "Resource id #1", where 1 is the resource number assigned to the resource by PHP at runtime. While the exact structure of this string should not be relied on and is subject to change, it will always be unique for a given resource within the lifetime of a script being executed (ie a Web request or CLI process) and won't be reused. To get a resource's type, use the get_resource_type() function.

null is always converted to an empty string.

As stated above, directly converting an array, object, or resource to a string does not provide any useful information about the value beyond its type. See the functions print_r() and var_dump() for more effective means of inspecting the contents of these types.

Most PHP values can also be converted to strings for permanent storage. This method is called serialization, and is performed by the serialize() function.

Details of the String Type

The string in PHP is implemented as an array of bytes and an integer indicating the length of the buffer. It has no information about how those bytes translate to characters, leaving that task to the programmer. There are no limitations on the values the string can be composed of; in particular, bytes with value 0 (“NUL bytes”) are allowed anywhere in the string (however, a few functions, said in this manual not to be “binary safe”, may hand off the strings to libraries that ignore data after a NUL byte.)

This nature of the string type explains why there is no separate “byte” type in PHP – strings take this role. Functions that return no textual data – for instance, arbitrary data read from a network socket – will still return strings.

Given that PHP does not dictate a specific encoding for strings, one might wonder how string literals are encoded. For instance, is the string "á" equivalent to "\xE1" (ISO-8859-1), "\xC3\xA1" (UTF-8, C form), "\x61\xCC\x81" (UTF-8, D form) or any other possible representation? The answer is that string will be encoded in whatever fashion it is encoded in the script file. Thus, if the script is written in ISO-8859-1, the string will be encoded in ISO-8859-1 and so on. However, this does not apply if Zend Multibyte is enabled; in that case, the script may be written in an arbitrary encoding (which is explicitly declared or is detected) and then converted to a certain internal encoding, which is then the encoding that will be used for the string literals. Note that there are some constraints on the encoding of the script (or on the internal encoding, should Zend Multibyte be enabled) – this almost always means that this encoding should be a compatible superset of ASCII, such as UTF-8 or ISO-8859-1. Note, however, that state-dependent encodings where the same byte values can be used in initial and non-initial shift states may be problematic.

Of course, in order to be useful, functions that operate on text may have to make some assumptions about how the string is encoded. Unfortunately, there is much variation on this matter throughout PHP’s functions:

  • Some functions assume that the string is encoded in some (any) single-byte encoding, but they do not need to interpret those bytes as specific characters. This is case of, for instance, substr(), strpos(), strlen() or strcmp(). Another way to think of these functions is that operate on memory buffers, i.e., they work with bytes and byte offsets.
  • Other functions are passed the encoding of the string, possibly they also assume a default if no such information is given. This is the case of htmlentities() and the majority of the functions in the mbstring extension.
  • Others use the current locale (see setlocale()), but operate byte-by-byte.
  • Finally, they may just assume the string is using a specific encoding, usually UTF-8. This is the case of most functions in the intl extension and in the PCRE extension (in the last case, only when the u modifier is used).

Ultimately, this means writing correct programs using Unicode depends on carefully avoiding functions that will not work and that most likely will corrupt the data and using instead the functions that do behave correctly, generally from the intl and mbstring extensions. However, using functions that can handle Unicode encodings is just the beginning. No matter the functions the language provides, it is essential to know the Unicode specification. For instance, a program that assumes there is only uppercase and lowercase is making a wrong assumption.

add a note

User Contributed Notes 23 notes

up
438
John
7 years ago
I've been a PHP programmer for a decade, and I've always been using the "single-quoted literal" and "period-concatenation" method of string creation. But I wanted to answer the performance question once and for all, using sufficient numbers of iterations and a modern PHP version. For my test, I used:

php -v
PHP 7.0.12 (cli) (built: Oct 14 2016 09:56:59) ( NTS )
Copyright (c) 1997-2016 The PHP Group
Zend Engine v3.0.0, Copyright (c) 1998-2016 Zend Technologies

------ Results: -------

* 100 million iterations:

$outstr = 'literal' . $n . $data . $int . $data . $float . $n;
63608ms (34.7% slower)

$outstr = "literal$n$data$int$data$float$n";
47218ms (fastest)

$outstr =<<<EOS
literal$n$data$int$data$float$n
EOS;
47992ms (1.64% slower)

$outstr = sprintf('literal%s%s%d%s%f%s', $n, $data, $int, $data, $float, $n);
76629ms (62.3% slower)

$outstr = sprintf('literal%s%5$s%2$d%3$s%4$f%s', $n, $int, $data, $float, $data, $n);
96260ms (103.9% slower)

* 10 million iterations (test adapted to see which of the two fastest methods were faster at adding a newline; either the PHP_EOL literal, or the \n string expansion):

$outstr = 'literal' . $n . $data . $int . $data . $float . $n;
6228ms (reference for single-quoted without newline)

$outstr = "literal$n$data$int$data$float$n";
4653ms (reference for double-quoted without newline)

$outstr = 'literal' . $n . $data . $int . $data . $float . $n . PHP_EOL;
6630ms (35.3% slower than double-quoted with \n newline)

$outstr = "literal$n$data$int$data$float$n\n";
4899ms (fastest at newlines)

* 100 million iterations (a test intended to see which one of the two ${var} and {$var} double-quote styles is faster):

$outstr = 'literal' . $n . $data . $int . $data . $float . $n;
67048ms (38.2% slower)

$outstr = "literal$n$data$int$data$float$n";
49058ms (1.15% slower)

$outstr = "literal{$n}{$data}{$int}{$data}{$float}{$n}"
49221ms (1.49% slower)

$outstr = "literal${n}${data}${int}${data}${float}${n}"
48500ms (fastest; the differences are small but this held true across multiple runs of the test, and this was always the fastest variable encapsulation style)

* 1 BILLION iterations (testing a completely literal string with nothing to parse in it):

$outstr = 'literal string testing';
23852ms (fastest)

$outstr = "literal string testing";
24222ms (1.55% slower)

It blows my mind. The double-quoted strings "which look so $slow since they have to parse everything for \n backslashes and $dollar signs to do variable expansion", turned out to be the FASTEST string concatenation method in PHP - PERIOD!

Single-quotes are only faster if your string is completely literal (with nothing to parse in it and nothing to concatenate), but the margin is very tiny and doesn't matter.

So the "highest code performance" style rules are:

1. Always use double-quoted strings for concatenation.

2. Put your variables in "This is a {$variable} notation", because it's the fastest method which still allows complex expansions like "This {$var['foo']} is {$obj->awesome()}!". You cannot do that with the "${var}" style.

3. Feel free to use single-quoted strings for TOTALLY literal strings such as array keys/values, variable values, etc, since they are a TINY bit faster when you want literal non-parsed strings. But I had to do 1 billion iterations to find a 1.55% measurable difference. So the only real reason I'd consider using single-quoted strings for my literals is for code cleanliness, to make it super clear that the string is literal.

4. If you think another method such as sprintf() or 'this'.$var.'style' is more readable, and you don't care about maximizing performance, then feel free to use whatever concatenation method you prefer!
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12
BahmanMD
1 year ago
In PHP 8.2 using ${var} in strings is deprecated, use {$var} instead:

<?php
$juice
= "apple";

// Valid. Explicitly specify the end of the variable name by enclosing it in braces:
echo "He drank some juice made of {$juice}s.";
?>
up
106
gtisza at gmail dot com
12 years ago
The documentation does not mention, but a closing semicolon at the end of the heredoc is actually interpreted as a real semicolon, and as such, sometimes leads to syntax errors.

This works:

<?php
$foo
= <<<END
abcd
END;
?>

This does not:

<?php
foo
(<<<END
abcd
END;
);
// syntax error, unexpected ';'
?>

Without semicolon, it works fine:

<?php
foo
(<<<END
abcd
END
);
?>
up
25
garbage at iglou dot eu
7 years ago
You can use string like array of char (like C)

$a = "String array test";

var_dump($a);
// Return string(17) "String array test"

var_dump($a[0]);
// Return string(1) "S"

// -- With array cast --
var_dump((array) $a);
// Return array(1) { [0]=> string(17) "String array test"}

var_dump((array) $a[0]);
// Return string(17) "S"

- Norihiori
up
9
vseokdog at gmail dot com
4 years ago
Don't forget about new E_WARNING and E_NOTICE errors from PHP 7.1.x: they have been introduced when invalid strings are coerced using operators expecting numbers (+ - * / ** % << >> | & ^) or their assignment equivalents. An E_NOTICE is emitted when the string begins with a numeric value but contains trailing non-numeric characters, and an E_WARNING is emitted when the string does not contain a numeric value.

Example:
$foo = 1 + "bob-1.3e3";
$foo = "10.2 pigs " + 1.0;
Will produce: Warning: A non-numeric value encountered

Read more: https://www.php.net/manual/en/migration71.other-changes.php
up
14
sideshowAnthony at googlemail dot com
8 years ago
Something I experienced which no doubt will help someone . . .
In my editor, this will syntax highlight HTML and the $comment:

$html = <<<"EOD"
<b>$comment</b>
EOD;

Using this shows all the same colour:

$html = <<<EOD
<b>$comment</b>
EOD;

making it a lot easier to work with
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22
lelon at lelon dot net
19 years ago
You can use the complex syntax to put the value of both object properties AND object methods inside a string. For example...
<?php
class Test {
public
$one = 1;
public function
two() {
return
2;
}
}
$test = new Test();
echo
"foo {$test->one} bar {$test->two()}";
?>
Will output "foo 1 bar 2".

However, you cannot do this for all values in your namespace. Class constants and static properties/methods will not work because the complex syntax looks for the '$'.
<?php
class Test {
const
ONE = 1;
}
echo
"foo {Test::ONE} bar";
?>
This will output "foo {Test::one} bar". Constants and static properties require you to break up the string.
up
19
og at gams dot at
16 years ago
easy transparent solution for using constants in the heredoc format:
DEFINE('TEST','TEST STRING');

$const = get_defined_constants();

echo <<<END
{$const['TEST']}
END;

Result:
TEST STRING
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8
Ray.Paseur sometimes uses Gmail
5 years ago
md5('240610708') == md5('QNKCDZO')

This comparison is true because both md5() hashes start '0e' so PHP type juggling understands these strings to be scientific notation. By definition, zero raised to any power is zero.
up
13
steve at mrclay dot org
15 years ago
Simple function to create human-readably escaped double-quoted strings for use in source code or when debugging strings with newlines/tabs/etc.

<?php
function doubleQuote($str) {
$ret = '"';
for (
$i = 0, $l = strlen($str); $i < $l; ++$i) {
$o = ord($str[$i]);
if (
$o < 31 || $o > 126) {
switch (
$o) {
case
9: $ret .= '\t'; break;
case
10: $ret .= '\n'; break;
case
11: $ret .= '\v'; break;
case
12: $ret .= '\f'; break;
case
13: $ret .= '\r'; break;
default:
$ret .= '\x' . str_pad(dechex($o), 2, '0', STR_PAD_LEFT);
}
} else {
switch (
$o) {
case
36: $ret .= '\$'; break;
case
34: $ret .= '\"'; break;
case
92: $ret .= '\\\\'; break;
default:
$ret .= $str[$i];
}
}
}
return
$ret . '"';
}
?>
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4
php at richardneill dot org
11 years ago
Leading zeroes in strings are (least-surprise) not treated as octal.
Consider:
$x = "0123" + 0;
$y = 0123 + 0;
echo "x is $x, y is $y"; //prints "x is 123, y is 83"
in other words:
* leading zeros in numeric literals in the source-code are interpreted as "octal", c.f. strtol().
* leading zeros in strings (eg user-submitted data), when cast (implicitly or explicitly) to integer are ignored, and considered as decimal, c.f. strtod().
up
0
greenbluemoonlight at gmail dot com
3 years ago
<?php
\\Example # 10 Simple Syntax - Solution for the last "echo" line.

class people {
public
$john = "John Smith";
public
$jane = "Jane Smith";
public
$robert = "Robert Paulsen";

public
$smith = "Smith";
}

$people = new people();

echo
"$people->john then said hello to $people->jane.".PHP_EOL;
echo
"$people->john's wife greeted $people->robert.".PHP_EOL;
echo
"$people->robert greeted the two $people->smiths";
\\
Won't work
\\Outputs: Robert Paulsen greeted the two

/**Solution:**\

echo "$people->robert greeted the two $people->smith\x08s";

\\Will work
\\Outputs: Robert Paulsen greeted the two Smiths

?>
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2
necrodust44 at gmail dot com
10 years ago
String conversion to numbers.

Unfortunately, the documentation is not correct.

«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).»

It is not said and is not shown in examples throughout the documentation that, while converting strings to numbers, leading space characters are ignored, like with the strtod function.

<?php
echo " \v\f \r 1234" + 1; // 1235
var_export ("\v\f \r 1234" == "1234"); // true
?>

However, PHP's behaviour differs even from the strtod's. The documentation says that if the string contains a "e" or "E" character, it will be parsed as a float, and suggests to see the manual for strtod for more information. The manual says

«A hexadecimal number consists of a "0x" or "0X" followed by a nonempty sequence of hexadecimal digits possibly containing a radix character, optionally followed by a binary exponent. A binary exponent consists of a 'P' or 'p', followed by an optional plus or minus sign, followed by a nonempty sequence of decimal digits, and indicates multiplication by a power of 2.»

But it seems that PHP does not recognise the exponent or the radix character.

<?php
echo "0xEp4" + 1; // 15
?>

strtod also uses the current locale to choose the radix character, but PHP ignores the locale, and the radix character is always 2E. However, PHP uses the locale while converting numbers to strings.

With strtod, the current locale is also used to choose the space characters, I don't know about PHP.
up
5
atnak at chejz dot com
19 years ago
Here is a possible gotcha related to oddness involved with accessing strings by character past the end of the string:

$string = 'a';

var_dump($string[2]); // string(0) ""
var_dump($string[7]); // string(0) ""
$string[7] === ''; // TRUE

It appears that anything past the end of the string gives an empty string.. However, when E_NOTICE is on, the above examples will throw the message:

Notice: Uninitialized string offset: N in FILE on line LINE

This message cannot be specifically masked with @$string[7], as is possible when $string itself is unset.

isset($string[7]); // FALSE
$string[7] === NULL; // FALSE

Even though it seems like a not-NULL value of type string, it is still considered unset.
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3
chAlx at findme dot if dot u dot need
15 years ago
To save Your mind don't read previous comments about dates ;)

When both strings can be converted to the numerics (in ("$a" > "$b") test) then resulted numerics are used, else FULL strings are compared char-by-char:

<?php
var_dump
('1.22' > '01.23'); // bool(false)
var_dump('1.22.00' > '01.23.00'); // bool(true)
var_dump('1-22-00' > '01-23-00'); // bool(true)
var_dump((float)'1.22.00' > (float)'01.23.00'); // bool(false)
?>
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1
Richard Neill
16 years ago
Unlike bash, we can't do
echo "\a" #beep!

Of course, that would be rather meaningless for PHP/web, but it's useful for PHP-CLI. The solution is simple: echo "\x07"
up
0
headden at karelia dot ru
14 years ago
Here is an easy hack to allow double-quoted strings and heredocs to contain arbitrary expressions in curly braces syntax, including constants and other function calls:

<?php

// Hack declaration
function _expr($v) { return $v; }
$_expr = '_expr';

// Our playground
define('qwe', 'asd');
define('zxc', 5);

$a=3;
$b=4;

function
c($a, $b) { return $a+$b; }

// Usage
echo "pre {$_expr(1+2)} post\n"; // outputs 'pre 3 post'
echo "pre {$_expr(qwe)} post\n"; // outputs 'pre asd post'
echo "pre {$_expr(c($a, $b)+zxc*2)} post\n"; // outputs 'pre 17 post'

// General syntax is {$_expr(...)}
?>
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-4
jonijnm at example dot com
6 years ago
Both should work :(

<?php

class Testing {
public static
$VAR = 'static';
public const VAR =
'const';

public function
sayHelloStatic() {
echo
"hello: {$this::$VAR}";
}

public function
sayHelloConst() {
echo
"hello: {$this::VAR}"; //Parse error: syntax error, unexpected '}', expecting '['
}
}

$obj = new Testing();
$obj->sayHelloStatic();
$obj->sayHelloConst();
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-4
nospam at nospam dot com
7 years ago
Beware that consistent with "String conversion to numbers":

<?php

if ('123abc' == 123) echo '(intstr == int) incorrectly tests as true.';

// Because one side is a number, the string is incorrectly converted from intstr to int, which then matches the test number.

// True for all conditionals such as if and switch statements (probably also while loops)!

// This could be a huge security risk when testing/using/saving user input, while expecting and testing for only an integer.

// It seems the only fix is for 123 to be a string as '123' so no conversion happens.

?>
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-6
shd at earthling dot net
14 years ago
If you want a parsed variable surrounded by curly braces, just double the curly braces:

<?php
$foo
= "bar";
echo
"{{$foo}}";
?>

will just show {bar}. The { is special only if followed by the $ sign and matches one }. In this case, that applies only to the inner braces. The outer ones are not escaped and pass through directly.
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-7
bishop
17 years ago
You may use heredoc syntax to comment out large blocks of code, as follows:
<?php
<<<_EOC
// end-of-line comment will be masked... so will regular PHP:
echo (
$test == 'foo' ? 'bar' : 'baz');
/* c-style comment will be masked, as will other heredocs (not using the same marker) */
echo <<<EOHTML
This is text you'll never see!
EOHTML;
function defintion(
$params) {
echo 'foo';
}
class definition extends nothing {
function definition(
$param) {
echo 'do nothing';
}
}

how about syntax errors?; = gone, I bet.
_EOC;
?>

Useful for debugging when C-style just won't do. Also useful if you wish to embed Perl-like Plain Old Documentation; extraction between POD markers is left as an exercise for the reader.

Note there is a performance penalty for this method, as PHP must still parse and variable substitute the string.
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-5
Hayley Watson
6 years ago
Any single expression, however complex, that starts with $ (i.e., a variable) can be {}-embedded in a double-quoted string:

<?php

echo "The expression {$h->q()["x}"]->p(9 == 0 ? 17 : 42)} gets parsed just as well as " . $h->q()["x}"]->p(9 == 0 ? 17 : 42) . " does.";

?>
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-8
mark at manngo dot net
7 years ago
I though that it would be helpful to add this comment so that the information at least appears on the right page on the PHP site.

Note that if you intend to use a double-quoted string with an associative key, you may run into the T_ENCAPSED_AND_WHITESPACE error. Some regard this as one of the less obvious error messages.

An expression such as:

<?php
$fruit
=array(
'a'=>'apple',
'b'=>'banana',
// etc
);

print
"This is a $fruit['a']"; // T_ENCAPSED_AND_WHITESPACE
?>

will definitely fall to pieces.

You can resolve it as follows:

<?php
print "This is a $fruit[a]"; // unquote the key
print "This is a ${fruit['a']}"; // Complex Syntax
print "This is a {$fruit['a']}"; // Complex Syntax variation
?>

I have a personal preference for the last variation as it is more natural and closer to what the expression would be like outside the string.

It’s not clear (to me, at least) why PHP misinterprets the single quote inside the expression but I imagine that it has something to do with the fact quotes are not part of the value string — once the string is already being parsed the quotes just get in the way … ?
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