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Strings

A string is series of characters, therefore, 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 basic Unicode functionality.

Note: It is no problem for a string to become very large. PHP imposes no boundary on the size of a string ; the only limit is the available memory of the computer on which PHP is running.

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 before a single quote, or at the end of the string , double it (\\). Note that attempting to escape any other character will print the backslash too.

Note: Unlike the three other syntaxes, variables and escape sequences for special characters will not be expanded when they occur in single quoted string s.

<?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)
\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.

Warning

It is very important to note that the line with the closing identifier must contain 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 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 (possibly followed by a semicolon) 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.

Example #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.

Example #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;
?>

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 #3 Heredoc in arguments example

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

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

Example #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;
}
?>

PHP 5.3.0 also introduces the possibility for Heredoc's to use double quotes in declarings:

Example #5 Using double quotes in Heredoc

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

Note: Heredoc support was added in PHP 4.

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 #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;
?>

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

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

Example #7 Static data example

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

Note: 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 was introduced in PHP 4, and can be recognised by the curly braces surrounding the expression.

Simple syntax

If a dollar sign ($) is encountered, the parser will greedily take as 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
$beer 
'Heineken';
echo 
"$beer's taste is great"// works; "'" is an invalid character for variable names
echo "He drank some $beers";   // won't work; 's' is a valid character for variable names but the variable is "$beer"
echo "He drank some ${beer}s"// works
echo "He drank some {$beer}s"// works
?>

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.

<?php
// These examples are specific to using arrays inside of strings.
// When outside of a string, always quote array string keys and do not use
// {braces}.

// Show all errors
error_reporting(E_ALL);

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

// Works, but note that this works differently outside a string
echo "A banana is $fruits[banana].";

// Works
echo "A banana is {$fruits['banana']}.";

// Works, but PHP looks for a constant named banana first, as described below.
echo "A banana is {$fruits[banana]}.";

// Won't work, use braces.  This results in a parse error.
echo "A banana is $fruits['banana'].";

// Works
echo "A banana is " $fruits['banana'] . ".";

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

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

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

Complex (curly) syntax

This isn't called complex because the syntax is complex, but because it allows for the use of complex expressions.

In fact, any value in the namespace can be included in a string with 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
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()}}";
?>

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: 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.

Note: String s may also be accessed using braces, as in $str{42}, for the same purpose. However, this syntax is deprecated as of PHP 5.3.0. Use square brackets instead, such as $str[42].

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_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 NUL byte.

Example #8 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';

?>

Note: Accessing variables of other types using [] or {} silently returns NULL.

Useful functions and operators

String s 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 float s). Floating point numbers can be converted using exponential notation (4.1E+6).

Note: The decimal point character is defined in the script's locale (category LC_NUMERIC). See the setlocale() function.

Array s 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.

Object s 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.

Resource s are always converted to string s with the structure "Resource id #1", where 1 is the unique number assigned to the resource by PHP at runtime. Do not rely upon this structure; it is subject to change. 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.


User Contributed Notes
Strings
saamde at gmail dot com
27-May-2010 10:40
Watch out for the "unexpected T_SL" error.  This appears to occur when there is white space just after "<<<EOT" and since it's white space it's real hard to spot the error in your code.
gt3
21-Mar-2010 09:06
If you try to embed backticks (AKA backquotes) inside of a heredoc, it won't treat the backticks as a shell command execution operator:

    echo <<<_HTML_
        <pre>`ls -l`</pre>
    _HTML_;

the above example will simply output the literal string 'ls -l' rather than running the command and outputting the results.

To interpolate shell command data you first have to store the returned backtick'd info in variables, then place the variables inside the heredoc:

    $cmd1 = `ls -l`;
    $cmd2 = shell_exec("netstat"); // same thing as backticks
    echo <<<_HTML_
        <pre>$cmd1 <hr> $cmd2</pre>
     _HTML_;
&#34;Sascha Ziemann&#34;
17-Dec-2009 09:58
Empty strings seem to be no real strings, because they behave different to strings containing data. Here is an example.

It is possible to change a character at a specific position using the square bracket notation:
<?php
$str
= '0';
$str[0] = 'a';
echo
$str."\n"; // => 'a'
?>

It is also possible to change a character with does not exist, if the index is "behind" the end of the string:
<?php
$str
= '0';
$str[1] = 'a';
echo
$str."\n"; // => 0a
?>

But if you do that on an empty string, the string gets silently converted into an array:
<?php
$str
= '';
$str[0] = 'a';
echo
$str."\n"; // => Array
?>
shd at earthling dot net
20-Oct-2009 09:54
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.
deminy at deminy dot net
17-Sep-2009 04:08
Although current documentation says 'A string literal can be specified in four different ways: ...', actually there is a fifth way to specify a (binary) string:

<?php $binary = b'This is a binary string'; ?>

The above statement declares a binary string using the 'b' prefix, which is available since PHP 5.2.1. However, it will only have effect as of PHP 6.0.0, as noted on https://doc0.ru/phpe/function.is-binary.php .
Liesbeth
03-Sep-2009 08:54
If you need to emulate a nowdoc in PHP < 5.3, try using HTML mode and output capturing. This way '$' or '\n' in your string won't be a problem anymore (but unfortunately, '<?' will be).

<?php

// Start of script

ob_start(); ?>
  A text with '
quotes'
    and $$$dollars$$$.
<?php $input = ob_get_contents(); ob_end_clean();

// Do what you want with $input
echo "<pre>" . $input . "</pre>";

?>
headden at karelia dot ru
20-Jun-2009 07:43
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(...)}
?>
Jarobman
21-Mar-2009 09:20
One thing I have noticed (using PHP 5.2.4) is that alphanumeric text starting with letters or underscore without spaces and operators in PHP code without single or double quotes is interpreted as a string.  I noticed this when trying to access a member variable from an object and getting an integer returned on what I thought should have been a syntax error.  The text cannot correspond to most PHP keywords since that would generate a fatal error.

<?php
class MyObject
{
    private
$__internal_array = array();
   
//insert code for overloading __get(), __set(), etc. to
    //access items from $__internal_array
}

$object = new MyObject();

//thought this would give a syntax error, put param returned an int somehow
some_function($object-membervar);

//correct
echo hiImAString;

//correct
echo hello.world._6789;

//correct
thisisastandalonestring;

//correct, outputs 0
echo string+anotherstring-yetanotherstring;

//correct, outputs 1concatenated
echo true.false.concatenated;

//incorrect, syntax error
echo cantdothis.1234567890;

//incorrect, syntax error, use of PHP keywords
echo try.and.do.this.if.you.can.else.break;
?>

Any other combination of the above with operators and other special characters will generate fatal errors.  I think it would be the opinion of many people that this form of a string is not at all practical and should never be used at all.  Personally, I think this looks like a bug, but I could be wrong.  However, this is something else one could watch out for when debugging since this is hard to pick up in code especially when expecting integer or boolean values.

Cheers,
Jarobman
cvolny at gmail dot com
03-Dec-2008 07:43
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.
Obeliks
16-Nov-2008 04:21
Expectedly <?php $string[$x] ?> and <?php substr($string, $x, 1) ?> will yield the same result... normally!

However, when you turn on the  Function Overloading Feature (http://de.php.net/manual/en/mbstring.overload.php), this might not be true!

If you use this Overloading Feature with 3rd party software, you should check for usage of the String access operator, otherwise you might be in for some nasty surprises.
Salil Kothadia
15-Oct-2008 08:33
An interesting finding about Heredoc "syntax error, unexpected $end".
I got this error because I did not use the php close tag "?>" and I had no code after the heredoc code.

foo1.php code gives "syntax error, unexpected $end".
But in foo2.php and foo3.php, when you add a php close tag or when you have some more code after heredoc it works fine.

Example Code:
foo1.php
1. <?php
2. $str
= <<<EOD
3. Example of string
4. spanning multiple lines
5. using heredoc syntax.
6. EOD;
7.

foo2.php
1. <?php
2.
$str = <<<EOD
3. Example of string
4. spanning multiple lines
5. using heredoc syntax.
6. EOD;
7.
8. echo
$str;
9.

foo3.php
1. <?php
2.
$str = <<<EOD
3. Example of string
4. spanning multiple lines
5. using heredoc syntax.
6. EOD;
7. ?>
steve at mrclay dot org
30-Sep-2008 08:33
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 . '"';
}
?>
chAlx at findme dot if dot u dot need
11-Sep-2008 03:42
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)
?>
harmor
01-Sep-2008 10:05
So you want to get the last character of a string using "String access and modification by character"?  Well negative indexes are not allowed so $str[-1] will return an empty string.

<?php
//Tested using: PHP 5.2.5

$str = 'This is a test.';

$last = $str[-1];                  //string(0) ""
$realLast = $str[strlen($str)-1];  //string(1) "."
$substr = substr($str,-1);         //string(1) "."

echo '<pre>';
var_dump($last);
var_dump($realLast);
var_dump($substr);
nullhility at gmail dot com
06-Jun-2008 07:40
It's also valuable to note the following:

<?php
${date("M")} = "Worked";
echo ${
date("M")};
?>

This is perfectly legal, anything inside the braces is executed first, the return value then becomes the variable name. Echoing the same variable variable using the function that created it results in the same return and therefore the same variable name is used in the echo statement. Have fun ;).
sk89q
30-Apr-2008 07:46
<?php
$F
= "F";
function
F($s) { return $s; }
$filename = '<some code>';
echo
"{$F(htmlspecialchars($filename))}";
?>
yuku
01-Apr-2008 02:21
This example of the heredoc has wrong output:
Code: This should print a capital 'A': \x41
Output should be: This should print a capital 'A': A

The example of the nowdoc has wrong code:
Code: This should not print a capital 'A': x41
That should be: This should not print a capital 'A': \x41
chris at chrisstockton dot org
24-Mar-2008 02:58
For anyone who reads Evan K, please note that:
// a string to test, and show the before and after
$before = 'Quantity:\t500\nPrice:\t$5.25 each';
$after = expand_escape($before);
var_dump($before, $after);

Is identical to (note all I added was a backslash before $):
$before = "Quantity:\t500\nPrice:\t\$5.25 each";
var_dump($before);

So its definitely better to escape a dollar instead of all the overhead of his regex and evals and such, although clever completely unnecessary.

-Chris
Evan K
28-Feb-2008 09:03
I encountered the odd situation of having a string containing unexpanded escape sequences that I wanted to expand, but also contained dollar signs that would be interpolated as variables.  "$5.25\n", for example, where I want to convert \n to a newline, but don't want attempted interpolation of $5.

Some muddling through docs and many obscenties later, I produced the following, which expands escape sequences in an existing string with NO interpolation.

<?php

// where we do all our magic
function expand_escape($string) {
    return
preg_replace_callback(
       
'/\\\([nrtvf]|[0-7]{1,3}|[0-9A-Fa-f]{1,2})?/',
       
create_function(
           
'$matches',
           
'return ($matches[0] == "\\\\") ? "" : eval( sprintf(\'return "%s";\', $matches[0]) );'
       
),
       
$string
   
);
}

// a string to test, and show the before and after
$before = 'Quantity:\t500\nPrice:\t$5.25 each';
$after = expand_escape($before);
var_dump($before, $after);

/* Outputs:
string(34) "Quantity:\t500\nPrice:\t$5.25 each"
string(31) "Quantity:    500
Price:    $5.25 each"
*/

?>
dot dot dot dot dot alexander at gmail dot com
07-Feb-2008 06:31
I think there's not that much to string comparison as claiming date recognition:

It's simply comparing ordinal values of the characters from the {0} to the {strlen-1} one.
In this case
<?php
$a
= '2007-11-06 15:17:48';
$b = '2007-11-05 15:17:48';

var_dump($a > $b);
?>
mArIo@luigi ~ $: php test.php
bool(true)
here all characters match till it reaches position 9 (the "day")
there, 6 has a bigger ord()inal value than 5

<?php
$a
= 'January 25th, 2008 00:23:38';
$b = 'Janury 24th, 2008 00:23:37'; // ($a > $b) === false
?>
Here when we reach 'r' in "Janury" we see that "a" is "less" than "r" so the example would evaluate as ($a < $b) === true

Here:
<?php
$a
= 'February 1st, 2008 00:23:38';
$b = 'January 25th, 2008 00:23:38';
?>
as expected the letter "F" comes before "J" as an ordinal character, so $a is less than $b
 Even here:
<?php
var_dump
('Z' > 'M'); //bool(true)
?>
it gets confirmed that the string comparison operators >, <, =>, =<, == just do a ordinal character comparison starting from position {0} to the first difference or the end of the string.
topnotcher at mail dot uri dot edu
28-Jan-2008 04:25
@qriz at example dot com

Numerical comparisons, such as <, > are simply _NOT_ valid on strings.  Thus, before a comparison can be made by a numerical comparison operator, the operands must be _casted_ to a numerical type (either float or int).  What I was attempting to say in my previous post is that >, < are date-aware; the tests I included were examples, and not intended to represent the full scope of my comparison.

"Works correctly since there is a comparing between strings. The comparisson is done on the last number/letter (since thats the only thing that is difference in the string) and that is in this case: the 9 and 8."

What you say here is mere assumption; a few quick tests show that this is indeed not the case.  If PHP indeed compares only the last character in the string, then the following assertion should be false:

test.php:
<?php
$a
= '2007-11-06 15:17:48';
$b = '2007-11-05 15:17:48';

var_dump($a > $b);
?>
mArIo@luigi ~ $: php test.php
bool(true)

Further, consider the following choices for $a and $b, which, as expected, demonstrate that the <, > operators can indeed understand date formats:

<?php
$a
= 'January 25th, 2008 00:23:37';
$b = 'January 24th, 2008 00:23:38'; // ($a > $b) === true, but 8
?>

If you remain unconvinced, consider what happens if I spell January incorrectly:

<?php
$a
= 'January 25th, 2008 00:23:38';
$b = 'Janury 24th, 2008 00:23:37'; // ($a > $b) === false
?>

Looks like it can understand ISO 8601 date formats? (for more information, see http://en.wikipedia.org/wiki/ISO_8601)

Further investigation yields that this doesn't even work as it should:
<?php
$a
= 'February 1st, 2008 00:23:38';
$b = 'January 25th, 2008 00:23:38';

var_dump($a > $b); //bool(false)

var_dump(strtotime($a)); //int(1201843418)
var_dump(strtotime($b)); //int(1201238618)
var_dump(strtotime($a) - strtotime($b)); //int(604800)
?>
Keeping $b constant and varying the month in $a shows that this comparison correctly interprets the date with the following months: January,March,May,June,July,September,October,November.  Interestingly enough, these are all the months having the property that ord($a[0]) >= ord($b[0]).

<?php
var_dump
('Z' > 'M'); //bool(true)
?>

Conclusion:
The <,> comparison operators definitely have functionality that is undocumented, including date awareness; however, this functionality may not always work as expected and should not be trusted for portability.
yuchunjiang at gmail dot com
23-Jan-2008 02:38
this is the sql string that use the variable and and \' and function.It generate the correct result.
 
$sql1=<<<EOT
INSERT INTO hp_visitHistory ( col1,col2,col3)
VALUES ( NOW(), '{$col2}', '{$_SERVER['REQUEST_URI']}')
EOT;
echo $sql1;
qriz at example dot com
13-Nov-2007 05:54
<?php
$a
= '2007-11-05 15:17:49';
$b = '2007-11-05 15:17:48';

$bool = $a > $b;

var_dump($bool); //bool(true)
?>

works correctly since there is a comparing between strings. The comparisson is done on the last number/letter (since thats the only thing that is difference in the string) and that is in this case: the 9 and 8.

8 > 9 = true

if you want to compare the string as pure numbers then you must type cast it to numbers or type juggle it:

<?php
$a
= '2007-11-05 15:17:49';
$b = '2007-11-05 15:17:48';

$bool1 = ($a + 0) > ($b + 0);      // 2007 > 2007
$bool2 = (int) $a > (int) $b;        // 2007 > 2007
$bool3 = intval($a) > intval($b);  // 2007 > 2007

var_dump($bool1,$bool2,$bool3); //bool(false)
?>
topnotcher at mail dot uri dot edu
06-Nov-2007 12:48
I have come across this several times, and as far as I can tell, the < and > operators have undocumented functionality when it comes to comparing strings.  Consider the following script:

<?php
$a
= '2007-11-05 15:17:49';
$b = '2007-11-05 15:17:48';

$bool = $a > $b;

var_dump($bool); //bool(true)

/**
 * The manual tells us that $a and $b should be
 * truncated at -, thus giving a floating-point value of 2007.
 * But (2007 > 2007) === false...
 */
$a = (float)$a;
$b = (float)$b;

var_dump($a); //float(2007);
var_dump($b); //float(2007);

/**
 * And the manual is right. So why does it correctly
 * compare the dates (which should be treated
 * as normal strings? Clearly some hidden functionality...
 */
rkfranklin+php at gmail dot com
26-Sep-2007 07:35
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>";
?>
michael at mahemoff dot com
07-Jul-2007 07:51
Heredocs can be used for more than just echoing or setting variables - use them whenever you want to include a string.

function header() {
  return <<<EOT
    <html>
      <head>
        <title>This is my heredoc</title>
      </head>
      <body>
EOT;

Also, note the strict syntax:
- No semicolon after initial EOT (think of the heredoc as a literal string arg - you wouldn't want a semicolon in front of it, would you?)
- BUT need semicolon after final EOT (the command is finished here)
- Final EOT is on the left margin - don't indent it!
php at craigbuchek dot com
03-Jul-2007 09:32
Function calls within double-quote variable interpolation work in PHP 5, but not quite as you'd expect. Basically the function has to be a variable function. I.e. a variable that holds the name of a function. So if you've got a function named 'x' that you want to call, you'll have to assign the function name to a variable. It's easiest to just assign it to a variable with the same name:

function x () { return 4; }
$x = 'x';
echo "x = {$x()}";

I'm not sure what the point of that is though, since it would be easier to do it this way:

function x () { return 4; }
$x = x();
echo "x = $x";
Richard Neill
01-Jun-2007 03:31
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"
og at gams dot at
26-Apr-2007 12:06
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
penda ekoka
24-Apr-2007 05:14
error control operator (@) with heredoc syntax:

the error control operator is pretty handy for supressing minimal errors or omissions. For example an email form that request some basic non mandatory information to your users. Some may complete the form, other may not. Lets say you don't want to tweak PHP for error levels and you just wish to create some basic template that will be emailed to the admin with the user information submitted. You manage to collect the user input in an array called $form:

<?php
// creating your mailer
$mailer = new SomeMailerLib();
$mailer->from = ' System <mail@yourwebsite.com>';
$mailer->to = 'admin@yourwebsite.com';
$mailer->subject = 'New user request';
// you put the error control operator before the heredoc operator to suppress notices and warnings about unset indices like this
$mailer->body = @<<<FORM
Firstname = {$form['firstname']}
Lastname =
{$form['lastname']}
Email =
{$form['email']}
Telephone =
{$form['telephone']}
Address =
{$form['address']}
FORM;

?>
php at moechofe dot com
01-Apr-2007 03:44
A simple benchmark to check differents about :
- simple and double quote concatenation and
- double quote and heredoc replacement

<?php

function test_simple_quote_concat()
{
 
$b = 'string';
 
$a  = ' string'.$b.' string'.$b.' srting'.$b;
 
$a .= ' string'.$b.' string'.$b.' string'.$b;
 
$a .= ' string'.$b.' string'.$b.' string'.$b;
 
$a .= ' string'.$b.' string'.$b.' string'.$b;
 
$a .= ' string'.$b.' string'.$b.' string'.$b;
 
$a .= ' string'.$b.' string'.$b.' string'.$b;
 
$a .= ' string'.$b.' string'.$b.' string'.$b;
 
$a .= ' string'.$b.' string'.$b.' string'.$b;
}

function
test_double_quote_concat()
{
 
$b = "string";
 
$a  = " string".$b." string".$b." string".$b;
 
$a .= " string".$b." string".$b." string".$b;
 
$a .= " string".$b." string".$b." string".$b;
 
$a .= " string".$b." string".$b." string".$b;
 
$a .= " string".$b." string".$b." string".$b;
 
$a .= " string".$b." string".$b." string".$b;
 
$a .= " string".$b." string".$b." string".$b;
 
$a .= " string".$b." string".$b." string".$b;
}

function
test_double_quote_replace()
{
 
$b = "string";
 
$a = " string$b string$b string$b
string
$b string$b string$b
string
$b string$b string$b
string
$b string$b string$b
string
$b string$b string$b
string
$b string$b string$b
string
$b string$b string$b
string
$b string$b string$b";
}

function
test_eot_replace()
{
 
$b = <<<EOT
string
EOT;
 
$a = <<<EOT
string{$b} string{$b} string{$b}
string
{$b} string{$b} string{$b}
string
{$b} string{$b} string{$b}
string
{$b} string{$b} string{$b}
string
{$b} string{$b} string{$b}
string
{$b} string{$b} string{$b}
string
{$b} string{$b} string{$b}
string
{$b} string{$b} string{$b}
EOT;
}

$iter = 2000;

for(
$i=0; $i<$iter; $i++ )
 
test_simple_quote_concat();

for(
$i=0; $i<$iter; $i++ )
 
test_double_quote_concat();

for(
$i=0; $i<$iter; $i++ )
 
test_double_quote_replace();

for(
$i=0; $i<$iter; $i++ )
 
test_eot_replace();

?>

I've use xdebug profiler to obtain the followed results:

test_simple_quote_concat : 173ms
test_double_quote_concat : 161ms
test_double_quote_replace : 147ms
test_eot_replace : 130ms
bryant at zionprogramming dot com
27-Feb-2007 08:16
As of (at least) PHP 5.2, you can no longer convert an object to a string unless it has a __toString method. Converting an object without this method now gives the error:

PHP Catchable fatal error:  Object of class <classname> could not be converted to string in <file> on line <line>

Try this code to get the same results as before:

<?php

if (!is_object($value) || method_exists($value, '__toString')) {
   
$string = (string)$value;
} else {
   
$string = 'Object';
}

?>
fmouse at fmp dot com
21-Feb-2007 06:20
It may be obvious to some, but it's convenient to note that variables _will_ be expanded inside of single quotes if these occur inside of a double-quoted string.  This can be handy in constructing exec calls with complex data to be passed to other programs.  e.g.:

$foo = "green";
echo "the grass is $foo";
the grass is green

echo 'the grass is $foo';
the grass is $foo

echo "the grass is '$foo'";
the grass is 'green'
bishop
28-Mar-2006 08:58
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.
webmaster at rephunter dot net
30-Nov-2005 04:57
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;
DELETETHIS dot php at dfackrell dot mailshell dot com
01-Nov-2005 04:05
Just some quick observations on variable interpolation:

Because PHP looks for {? to start a complex variable expression in a double-quoted string, you can call object methods, but not class methods or unbound functions.

This works:

<?php
class a {
    function
b() {
        return
"World";
    }
}
$c = new a;
echo
"Hello {$c->b()}.\n"
?>

While this does not:

<?php
function b() {
    return
"World";
}
echo
"Hello {b()}\n";
?>

Also, it appears that you can almost without limitation perform other processing within the argument list, but not outside it.  For example:

<?
$true
= true;
define("HW", "Hello World");
echo
"{$true && HW}";
?>

gives: Parse error: parse error, unexpected T_BOOLEAN_AND, expecting '}' in - on line 3

There may still be some way to kludge the syntax to allow constants and unbound function calls inside a double-quoted string, but it isn't readily apparent to me at the moment, and I'm not sure I'd prefer the workaround over breaking out of the string at this point.
lelon at lelon dot net
27-Oct-2004 07:01
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.
Jonathan Lozinski
06-Aug-2004 07:03
A note on the heredoc stuff.

If you're editing with VI/VIM and possible other syntax highlighting editors, then using certain words is the way forward.  if you use <<<HTML for example, then the text will be hightlighted for HTML!!

I just found this out and used sed to alter all EOF to HTML.

JAVASCRIPT also works, and possibly others.  The only thing about <<<JAVASCRIPT is that you can't add the <script> tags..,  so use HTML instead, which will correctly highlight all JavaScript too..

You can also use EOHTML, EOSQL, and EOJAVASCRIPT.
www.feisar.de
28-Apr-2004 02:49
watch out when comparing strings that are numbers. this example:

<?php

$x1
= '111111111111111111';
$x2 = '111111111111111112';

echo (
$x1 == $x2) ? "true\n" : "false\n";

?>

will output "true", although the strings are different. With large integer-strings, it seems that PHP compares only the integer values, not the strings. Even strval() will not work here.

To be on the safe side, use:

$x1 === $x2
atnak at chejz dot com
11-Apr-2004 10:53
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.
dandrake
19-Jan-2004 11:41
By the way, the example with the "\n" sequence will insert a new line in the html code, while the output will be decided by the HTML syntax. That's why, if you use

<?
 
echo "Hello \n World";
?>

the browser will receive the HTML code on 2 lines
but his output on the page will be shown on one line only.
To diplay on 2 lines simply use:

<?
 
echo "Hello <br>World";
?>

like in HTML.
philip at cornado dot com
12-Apr-2003 12:37
Note that in PHP versions 4.3.0 and 4.3.1, the following provides a bogus E_NOTICE (this is a known bug):

echo "$somearray['bar']";

This is accessing an array inside a string using a quoted key and no {braces}.  Reading the documention shows all the correct ways to do this but the above will output nothing on most systems (most have E_NOTICE off) so users may be confused.  In PHP 4.3.2, the above will again yield a parse error.
03-Mar-2003 06:04
Regarding "String access by character":

Apparently if you edit a specific character in a string, causing the string to be non-continuous, blank spaces will be added in the empty spots.

echo '<pre>';
$str = '0123';
echo "$str\n";
$str[4] = '4';
echo "$str\n";
$str[6] = '6';
echo "$str\n";

This will output:
0123
01234
01234 6
Notice the blank space where 5 should be.
vallo at cs dot helsinki dot fi
04-Nov-2002 01:41
Even if the correct way to handle variables is determined from the context, some things just doesn't work without doing some preparation.

I spent several hours figuring out why I couldn't index a character out of a string after doing some math with it just before. The reason was that PHP thought the string was an integer!

$reference = $base + $userid;
.. looping commands ..
$chartohandle = $reference{$last_char - $i};

Above doesn't work. Reason: last operation with $reference is to store a product of an addition -> integer variable. $reference .=""; (string catenation) had to be added before I got it to work:

$reference = $base + $userid;
$reference .= "";
.. looping commands ..
$chartohandle = $reference{$last_char - $i};

Et voilá! Nice stream of single characters.
guidod at gmx dot de
23-Jul-2002 06:26
PHP's double-quoted strings are inherently ill-featured - they will be a problem especially with computed code like in /e-evals with preg_replace.

bash and perl follow the widely accepted rule that all backslashes will escape the nextfollowing char, and nonalpha-chars will always get printed there as themselves whereas (the unescaped chars might have special meaning in regex). Anyway, it is a great way to just escape all nonalpha chars that you uncertain about whether they have special meaning in some places, and ye'll be sure they will get printed literal.

Furthermore, note that \{ sequence is not mentioned in the  escape-char table! You'll get to know about it only "complex (curly) syntax". This can even more be a problem with evals, as they behave rather flaky like it _cannot_ be accomodated for computed code. Try all variants of `echo "hello \{\$world}"` removing one or more of the chars in the \{\$ part - have fun!
 

 
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