Рядковий (Strings)

Рядковий тип (string) представляє собою набір символів, причому кожен символ представлений відповідним байтом. Це означає, що PHP має підтримку всього 256 різних символів, а отже не має вбудованої підтримки Unicode. Див. деталі про рядковий тип.

Зауваження: Значення рядкового типу (string) може бути розміром до 2ГБ (максимум 2147483647 байт)

Синтаксис

Якщо записувати значення рядкового типу (string) літерами, то це можна зробити в чотири різні способи:

Одинарні лапки

Найпростіший спосіб визначити рядкове значення (string) - взяти його в одинарні лапки (наприклад 'це рядкове значення').

Щоб всередині рядкового значення впасати одинарні лапки, екрануйте їх через зворотній слеш (\). Щоб всередині рядкового значення вписати зворотній слеш, продублюйте його (\\). Всі наступні символи зворотнього слеша будуть сприйматись буквально як зворотні слеші: це означає, що всі інші екрановані послідовності можна використовувати також, такі як \r або \n, будуть виводитись буквально як вони записані, а не як такі, які мають спеціальне значення.

Зауваження: Unlike the double-quoted and heredoc syntaxes, variables and escape sequences for special characters will not be expanded when they occur in single quoted (string).

<?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 more 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) (since PHP 5.2.5)
\e escape (ESC or 0x1B (27) in ASCII) (since PHP 5.4.4)
\f form feed (FF or 0x0C (12) in ASCII) (since PHP 5.2.5)
\\ 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

As in single quoted (string)s, escaping any other character will result in the backslash being printed too. Before PHP 5.1.1, the backslash in \{$var} had not been printed.

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

Heredoc

A third way to delimit (string)s 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 must begin in the first column of the line. Also, the 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.

Увага

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 Mac OS X. 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.

Heredocs can not be used for initializing class properties. Since PHP 5.3, this limitation is valid only for heredocs containing variables.

Приклад #1 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 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 (string)s.

Приклад #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;
?>

Наведений вище приклад виведе:

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:

Приклад #3 Heredoc in arguments example

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

As of PHP 5.3.0, it's possible to initialize static variables and class properties/constants using the Heredoc syntax:

Приклад #4 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;
}
?>

Starting with PHP 5.3.0, the opening Heredoc identifier may optionally be enclosed in double quotes:

Приклад #5 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.

Приклад #6 Nowdoc string quoting example

<?php
$str 
= <<<'EOD'
Example of string
spanning multiple lines
using nowdoc syntax.
EOD;

/* More complex example, with variables. */
class foo
{
    public 
$foo;
    public 
$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 not print a capital 'A': \x41
EOT;
?>

Наведений вище приклад виведе:

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

Зауваження:

Unlike heredocs, nowdocs can be used in any static data context. The typical example is initializing class properties or constants:

Приклад #7 Static data example

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

Зауваження:

Nowdoc support was added in PHP 5.3.0.

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;
// Invalid. "s" is a valid character for a variable name, but the variable is $juice.
echo "He drank some juice made of $juices.";
?>

Наведений вище приклад виведе:

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

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.

Приклад #8 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
?>

Наведений вище приклад виведе:

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 .

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. Simply write the expression the same way as it would appear outside the (string), and then wrap it 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}";
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()}";
?>

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";
?>

Наведений вище приклад виведе:

I am bar.
I am bar.

Зауваження:

Functions, method calls, static class variables, and class constants inside {$} work since PHP 5. However, the value accessed 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 (string)s 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.

Зауваження: Strings may also be accessed using braces, as in $str{42}, for the same purpose.

Увага

Writing to an out of range offset pads the string with spaces. Non-integer types are converted to integer. Illegal offset type emits E_NOTICE. Negative offset emits E_NOTICE in write but reads empty string. Only the first character of an assigned string is used. Assigning empty string assigns NULL byte.

Увага

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.

Приклад #9 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';

?>

As of PHP 5.4 string offsets have to either be integers or integer-like strings, otherwise a warning will be thrown. Previously an offset like "foo" was silently cast to 0.

Приклад #10 Differences between PHP 5.3 and PHP 5.4

<?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']));
?>

Наведений вище приклад в PHP 5.3 виведе:

string(1) "b"
bool(true)
string(1) "b"
bool(true)
string(1) "a"
bool(true)
string(1) "b"
bool(true)

Наведений вище приклад в PHP 5.4 виведе:

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)

Зауваження:

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

Зауваження:

PHP 5.5 added support for accessing characters within string literals using [] or {}.

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 regular expression functions or the Perl-compatible regular expression functions for advanced find & replace functionality.

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

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 boolean TRUE value is converted to the (string) "1". Boolean FALSE is converted to "" (the empty string). This allows conversion back and forth between boolean and (string) values.

An integer 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).

Зауваження:

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.

Objects in PHP 4 are always converted to the (string) "Object". To print the values of object properties for debugging reasons, read the paragraphs below. To get an object's class name, use the get_class() function. As of PHP 5, the __toString method is used when applicable.

Resources are always converted to (string)s 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 (string)s for permanent storage. This method is called serialization, and is performed by the serialize() function. If the PHP engine was built with WDDX support, PHP values can also be serialized as well-formed XML text.

String conversion to numbers

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

If the (string) does not contain any of the characters '.', 'e', or 'E' and the numeric value fits into integer type limits (as defined by PHP_INT_MAX), the (string) will be evaluated as an integer. In all other cases it will be evaluated as a float.

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 
"10.5";                // $foo is float (11.5)
$foo "-1.3e3";              // $foo is float (-1299)
$foo "bob-1.3e3";           // $foo is integer (1)
$foo "bob3";                // $foo is integer (1)
$foo "10 Small Pigs";       // $foo is integer (11)
$foo "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).

To test any of the examples in this section, cut and paste the examples and insert the following line to see 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 is done in C. Use the ord() and chr() functions to convert between ASCII codes and characters.

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 explicity 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. This is the case of strcasecmp(), strtoupper() and ucfirst(). This means they can be used only with single-byte encodings, as long as the encoding is matched by the locale. For instance strtoupper("á") may return "Á" if the locale is correctly set and á is encoded with a single byte. If it is encoded in UTF-8, the correct result will not be returned and the resulting string may or may not be returned corrupted, depending on the current locale.
  • 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). Although this is due to their special purpose, the function utf8_decode() assumes a UTF-8 encoding and the function utf8_encode() assumes an ISO-8859-1 encoding.

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 add a note

User Contributed Notes 26 notes

up
370
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!
up
96
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
22
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
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
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
up
3
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
17
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
4
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
up
10
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)
?>
up
8
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(...)}
?>
up
6
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 . '"';
}
?>
up
1
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.

?>
up
1
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 … ?
up
3
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
4
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
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
3
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.
up
-3
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();
up
-3
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.
up
-3
rkfranklin+php at gmail dot com
16 years ago
If you want to use a variable in an array index within a double quoted string you have to realize that when you put the curly braces around the array, everything inside the curly braces gets evaluated as if it were outside a string.  Here are some examples:

<?php
$i
= 0;
$myArray[Person0] = Bob;
$myArray[Person1] = George;

// prints Bob (the ++ is used to emphasize that the expression inside the {} is really being evaluated.)
echo "{$myArray['Person'.$i++]}<br>";

// these print George
echo "{$myArray['Person'.$i]}<br>";
echo
"{$myArray["Person{$i}"]}<br>";

// These don't work
echo "{$myArray['Person$i']}<br>";
echo
"{$myArray['Person'$i]}<br>";

// These both throw fatal errors
// echo "$myArray[Person$i]<br>";
//echo "$myArray[Person{$i}]<br>";
?>
up
-2
webmaster at rephunter dot net
18 years ago
Use caution when you need white space at the end of a heredoc. Not only is the mandatory final newline before the terminating symbol stripped, but an immediately preceding newline or space character is also stripped.

For example, in the following, the final space character (indicated by \s -- that is, the "\s" is not literally in the text, but is only used to indicate the space character) is stripped:

$string = <<<EOT
this is a string with a terminating space\s
EOT;

In the following, there will only be a single newline at the end of the string, even though two are shown in the text:

$string = <<<EOT
this is a string that must be
followed by a single newline

EOT;
up
-4
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.
up
-5
cvolny at gmail dot com
15 years ago
I commented on a php bug feature request for a string expansion function and figured I should post somewhere it might be useful:

using regex, pretty straightforward:
<?php
function stringExpand($subject, array $vars) {
   
// loop over $vars map
   
foreach ($vars as $name => $value) {
       
// use preg_replace to match ${`$name`} or $`$name`
       
$subject = preg_replace(sprintf('/\$\{?%s\}?/', $name), $value,
$subject);
    }
   
// return variable expanded string
   
return $subject;
}
?>

using eval() and not limiting access to only certain variables (entire current symbol table including [super]globals):

<?php
function stringExpandDangerous($subject, array $vars = array(), $random = true) {
   
       
// extract $vars into current symbol table
       
extract($vars);
       
       
$delim;
       
// if requested to be random (default), generate delim, otherwise use predefined (trivially faster)
       
if ($random)
           
$delim = '___' . chr(mt_rand(65,90)) . chr(mt_rand(65,90)) . chr(mt_rand(65,90)) . chr(mt_rand(65,90)) . chr(mt_rand(65,90)) . '___';
        else
           
$delim = '__ASDFZXCV1324ZXCV__'// button mashing...
       
        // built the eval code
       
$statement = "return <<<$delim\n\n" . $subject . "\n$delim;\n";
       
       
// execute statement, saving output to $result variable
       
$result = eval($statement);
       
       
// if eval() returned FALSE, throw a custom exception
       
if ($result === false)
            throw new
EvalException($statement);
       
       
// return variable expanded string
       
return $result;
    }
?>

I hope that helps someone, but I do caution against using the eval() route even if it is tempting.  I don't know if there's ever a truely safe way to use eval() on the web, I'd rather not use it.
up
-7
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.";

?>
up
-20
M. H. S.
4 years ago
<?php

// Its A Example for "Heredoc":

$n = 10;

$var_heredoc = <<<HEREDOC

Its A String For "
$var_heredoc" variable.

heredoc can expanding variables.
(example:
$n)

if you want not expanding, you need print " \ " befor variable.
(example: /
$n)

heredoc can use " /n, /t, /r, ... ".

heredoc = the string of double-qoutation;

        HEREDOC; -> its bad closing of heredoc!

HEREDOC;
// its a good closing of heredoc!

?>
up
-3
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

?>
To Top