Floating point numbers
In response to sassospicco:
When you set the character to null it also changed the type to null, other users should note that if you want to set characters to null in this fashion that you should use an escape sequence to keep the variable as type string. Here's sassospicco's altered code with the null character (instead of NULL type), all output is as desired.
<?php
$a = 'AB';
echo strlen($a)."\n"; // 2
// Ok so far
$a[1] = "\x00";
echo strlen($a)."\n"; // 2
// The second character still exists...
var_dump($a); // string(2) "A"
echo ord($a[1]); //ASCII value: 0
?>
Strings
A string is series of characters. Before PHP 6, 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
- double quoted
- heredoc syntax
- nowdoc syntax (since PHP 5.3.0)
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 two other syntaxes, variables and escape sequences for special characters will not be expanded when they occur in single quoted strings.
<?php
echo 'this is a simple string';
echo 'You can also have embedded newlines in
strings this way as it is
okay to do';
// Outputs: Arnold once said: "I'll be back"
echo 'Arnold once said: "I\'ll be back"';
// Outputs: You deleted C:\*.*?
echo 'You deleted C:\\*.*?';
// Outputs: You deleted C:\*.*?
echo 'You deleted C:\*.*?';
// Outputs: This will not expand: \n a newline
echo 'This will not expand: \n a newline';
// Outputs: Variables do not $expand $either
echo 'Variables do not $expand $either';
?>
Double quoted
If the string is enclosed in double-quotes ("), PHP will interpret more escape sequences for special 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 strings, escaping any other character will result in the backslash being printed too. Before PHP 5.1.1, the backslash in \{$var} was not been printed.
The most important feature of double-quoted strings is the fact that variable names will be expanded. See string parsing for details.
Heredoc
A third way to delimit strings is the heredoc syntax: <<<. After this operator, an identifier is provided, then a newline. The string itself follows, and then the same identifier again to close the quotation.
The closing identifier 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 members. Use nowdocs instead.
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 strings.
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
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 <<< seqeuence 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 #3 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 members or constants:
Example #4 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
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 appeared 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()}}";
?>
Note: Functions and method calls inside {$} work since PHP 5.
String access and modification by character
Characters within strings may be accessed and modified by specifying the zero-based offset of the desired character after the string using square array brackets, as in $str[42]. Think of a string as an array of characters for this purpose.
Note: Strings may also be accessed using braces, as in $str{42}, for the same purpose. However, this syntax is deprecated as of PHP 6. Use square brackets instead.
Example #5 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
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).
Note: 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 members 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 strings 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 strings 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.
The string will be evaluated as a float if it contains any of the characters '.', 'e', or 'E'. Otherwise, it will be evaluated as an integer.
The value is given by the initial portion of the string. If the string starts with valid numeric data, this will be the value used. Otherwise, the value will be 0 (zero). Valid numeric data is an optional sign, followed by one or more digits (optionally containing a decimal point), followed by an optional exponent. The exponent is an 'e' or 'E' followed by one or more digits.
<?php
$foo = 1 + "10.5"; // $foo is float (11.5)
$foo = 1 + "-1.3e3"; // $foo is float (-1299)
$foo = 1 + "bob-1.3e3"; // $foo is integer (1)
$foo = 1 + "bob3"; // $foo is integer (1)
$foo = 1 + "10 Small Pigs"; // $foo is integer (11)
$foo = 4 + "10.2 Little Piggies"; // $foo is float (14.2)
$foo = "10.0 pigs " + 1; // $foo is float (11)
$foo = "10.0 pigs " + 1.0; // $foo is float (11)
?>
For more information on this conversion, see the Unix manual page for strtod(3).
To test any of the examples in this section, cut and paste the examples and insert the following line to see what's going on:
<?php
echo "\$foo==$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.
add a note
User Contributed NotesStrings
nullhility at gmail dot com
04-Jul-2008 01:51
04-Jul-2008 01:51
sassospicco
04-Jul-2008 12:03
04-Jul-2008 12:03
Note this behavior, accessing a character.
<?php
$a = 'AB';
strlen($a); // 2
// Ok so far
$a[1] = NULL;
strlen($a); // 2
// The second character still exists...
var_dump($a); // string(2) "A"
// ...but it is not displayed.
ord($a[1]); // 0
// ASCII value: 0
?>
nullhility at gmail dot com
06-Jun-2008 04:40
06-Jun-2008 04:40
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 04:46
30-Apr-2008 04:46
<?php
$F = "F";
function F($s) { return $s; }
$filename = '<some code>';
echo "{$F(htmlspecialchars($filename))}";
?>
yuku
31-Mar-2008 11:21
31-Mar-2008 11:21
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 11:58
24-Mar-2008 11:58
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 06:03
28-Feb-2008 06:03
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 03:31
07-Feb-2008 03:31
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 01:25
28-Jan-2008 01:25
@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
22-Jan-2008 11:38
22-Jan-2008 11:38
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 02:54
13-Nov-2007 02:54
<?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
05-Nov-2007 09:48
05-Nov-2007 09:48
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 04:35
26-Sep-2007 04:35
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 04:51
07-Jul-2007 04:51
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 06:32
03-Jul-2007 06:32
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 12:31
01-Jun-2007 12:31
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
25-Apr-2007 09:06
25-Apr-2007 09:06
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 02:14
24-Apr-2007 02:14
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 12:44
01-Apr-2007 12:44
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; $i++ )
test_eot_replace();
?>
I've use xdebug profiler to obtain the followed results:
test_simple_quote_concat : 173ms
test_double_quote_concat : 161ms
test_double_quote_replace : 147ms
test_eot_replace : 130ms
bryant at zionprogramming dot com
27-Feb-2007 05:16
27-Feb-2007 05:16
As of (at least) PHP 5.2, you can no longer convert an object to a string unless it has a __toString method. Converting an object without this method now gives the error:
PHP Catchable fatal error: Object of class <classname> could not be converted to string in <file> on line <line>
Try this code to get the same results as before:
<?php
if (!is_object($value) || method_exists($value, '__toString')) {
$string = (string)$value;
} else {
$string = 'Object';
}
?>
fmouse at fmp dot com
21-Feb-2007 03:20
21-Feb-2007 03:20
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 05:58
28-Mar-2006 05:58
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 01:57
30-Nov-2005 01:57
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 01:05
01-Nov-2005 01:05
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 04:01
27-Oct-2004 04:01
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 04:03
06-Aug-2004 04:03
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 11:49
28-Apr-2004 11:49
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 07:53
11-Apr-2004 07:53
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
$string[7] === NULL; // FALSE
Even though it seems like a not-NULL value of type string, it is still considered unset.
dandrake
19-Jan-2004 08:41
19-Jan-2004 08:41
By the way, the example with the "\n" sequence will insert a new line in the html code, while the output will be decided by the HTML syntax. That's why, if you use
<?
echo "Hello \n World";
?>
the browser will receive the HTML code on 2 lines
but his output on the page will be shown on one line only.
To diplay on 2 lines simply use:
<?
echo "Hello <br>World";
?>
like in HTML.
philip at cornado dot com
11-Apr-2003 09:37
11-Apr-2003 09:37
Note that in PHP versions 4.3.0 and 4.3.1, the following provides a bogus E_NOTICE (this is a known bug):
echo "$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 03:04
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
03-Nov-2002 10:41
03-Nov-2002 10:41
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 03:26
23-Jul-2002 03:26
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!