Useful functions in PHP

从手册上整理了一些有用且比较常用的php函数, 便于以后查阅.

1. htmlspecialchars

Convert special characters to HTML entities (PHP 4, PHP 5)

http://www.php.net/htmlspecialchars[/b]

string htmlspecialchars ( string $string [, int $quote_style [, string $charset [, bool $double_encode ]]] )

quote_style constants
ENT_COMPAT
Will convert double-quotes and leave single-quotes alone (default) 只处理双引号
ENT_QUOTES
Will convert both double and single quotes 处理双引号和单引号
ENT_NOQUOTES
Will leave both double and single quotes unconverted 不处理双引号和单引号
The translations performed are:

'&' (ampersand) becomes '&'

'"' (double quote) becomes '"' when ENT_NOQUOTES is not set.

''' (single quote) becomes ''' only when ENT_QUOTES is set.

'<' (less than) becomes '<'

'>' (greater than) becomes '>'

Example #1 htmlspecialchars() example

<?php
$new = htmlspecialchars("<a href='test'>Test</a>", ENT_QUOTES);
echo $new; // <a href='test'>Test</a>
?>
2. htmlspecialchars_decode

(PHP 5 >= 5.1.0)

htmlspecialchars_decode — Convert special HTML entities back to characters

Example #1 A htmlspecialchars_decode() example

<?php
$str = '<p>this -> "</p>';

echo htmlspecialchars_decode($str);

// note that here the quotes aren't converted
echo htmlspecialchars_decode($str, ENT_NOQUOTES);
?>
The above example will output:

<p>this -> "</p>
<p>this -> "</p>
3. htmlentities

(PHP 4, PHP 5)

htmlentities — Convert all applicable characters to HTML entities

Example #1 A htmlentities() example

<?php
$str = "A 'quote' is <b>bold</b>";

// Outputs: A 'quote' is <b>bold</b>
echo htmlentities($str);

// Outputs: A 'quote' is <b>bold</b>
echo htmlentities($str, ENT_QUOTES);
?>
4. html_entity_decode

(PHP 4 >= 4.3.0, PHP 5)

html_entity_decode — Convert all HTML entities to their applicable characters

Example #1 Decoding HTML entities

<?php
$orig = "I'll /"walk/" the <b>dog</b> now";

$a = htmlentities($orig);

$b = html_entity_decode($a);

echo $a; // I'll "walk" the <b>dog</b> now

echo $b; // I'll "walk" the <b>dog</b> now

// For users prior to PHP 4.3.0 you may do this:
function unhtmlentities($string)
{
// replace numeric entities
$string = preg_replace('~&#x([0-9a-f]+);~ei', 'chr(hexdec("//1"))', $string);
$string = preg_replace('~&#([0-9]+);~e', 'chr("//1")', $string);
// replace literal entities
$trans_tbl = get_html_translation_table(HTML_ENTITIES);
$trans_tbl = array_flip($trans_tbl);
return strtr($string, $trans_tbl);
}

$c = unhtmlentities($a);

echo $c; // I'll "walk" the <b>dog</b> now

?>
5. strip_tags

(PHP 4, PHP 5)

strip_tags — Strip HTML and PHP tags from a string

Description

string strip_tags ( string $str [, string $allowable_tags ] )
Example #1 strip_tags() example

<?php
$text = '<p>Test paragraph.</p><!-- Comment --> <a href="#fragment">Other text</a>';
echo strip_tags($text);
echo "/n";

// Allow <p> and <a>
echo strip_tags($text, '<p><a>');
?>
The above example will output:

Test paragraph. Other text
<p>Test paragraph.</p> <a href="#fragment">Other text</a>
6. nl2br

(PHP 4, PHP 5)

nl2br — Inserts HTML line breaks before all newlines in a string

Description

string nl2br ( string $string [, bool $is_xhtml ] )
Returns string with '<br />' or '<br>' inserted before all newlines.

Example #1 using nl2br()

<?php
echo nl2br("foo isn't/n bar");
?>
The above example will output:

foo isn't<br />
bar
Example #2 Generating valid HTML markup using the is_xhtml parameter

<?php
echo nl2br("Welcome/r/nThis is my HTML document", false);
?>
The above example will output:

Welcome<br>
This is my HTML document
7. urlencode

(PHP 4, PHP 5)

urlencode — URL-encodes string

Description

string urlencode ( string $str )
This function is convenient when encoding a string to be used in a query part of a URL, as a convenient way to pass variables to the next page.

Example #1 urlencode() example

<?php
$url = "www.google.com/?q=alka rani&start=100";
echo urlencode($url);
echo "<br/>";
echo rawurlencode($url);
echo "<br/>";
echo urldecode(urlencode($url));
echo "<br/>";
echo rawurldecode(rawurlencode($url));
echo "<br/>";
echo rawurldecode(urlencode($url));
echo "<br/>";
echo urldecode(rawurlencode($url));
?>

result:
www.google.com%2F%3Fq%3Dalka+rani%26start%3D100
www.google.com%2F%3Fq%3Dalka%20rani%26start%3D100
www.google.com/?q=alka rani&start=100
www.google.com/?q=alka rani&start=100
www.google.com/?q=alka+rani&start=100
www.google.com/?q=alka rani&start=100

8. urldecode
(PHP 4, PHP 5)

urldecode — Decodes URL-encoded string

Description

string urldecode ( string $str )
Decodes any %## encoding in the given string.

See also:
rawurlencode()
rawurldecode()

9.

addslashes

(PHP 4, PHP 5)

addslashes — Quote string with slashes

Description

string addslashes ( string $str )
Returns a string with backslashes before characters that need to be quoted in database queries etc. These characters are single quote ('), double quote ("), backslash (/) and NUL (the NULL byte).

The PHP directive magic_quotes_gpc is on by default, and it essentially runs addslashes() on all GET, POST, and COOKIE data. Do not use addslashes() on strings that have already been escaped with magic_quotes_gpc as you'll then do double escaping. The function get_magic_quotes_gpc() may come in handy for checking this.

Example #1 An addslashes() example

<?php
$str = "Is your name O'reilly?";

// Outputs: Is your name O/'reilly?
echo addslashes($str);
?>

10.

stripslashes

(PHP 4, PHP 5)

stripslashes — Un-quotes a quoted string

Description

string stripslashes ( string $str )
Un-quotes a quoted string.

Example #1 A stripslashes() example

<?php
$str = "Is your name O/'reilly?";

// Outputs: Is your name O'reilly?
echo stripslashes($str);
?>

See Also[/b]

[/b]addcslashes()
stripcslashes()
get_magic_quotes_gpc()

[/b]11. mysql_real_escape_string

(PHP 4 >= 4.3.0, PHP 5, PECL mysql:1.0)

mysql_real_escape_string — Escapes special characters in a string for use in a SQL statement

Description

string [b]mysql_real_escape_string ( string $unescaped_string [, resource $link_identifier ] )
Escapes special characters in the unescaped_string , taking into account the current character set of the connection so that it is safe to place it in a mysql_query(). If binary data is to be inserted, this function must be used.

mysql_real_escape_string() calls MySQL's library function mysql_real_escape_string, which prepends backslashes to the following characters: /x00, /n, /r, /, ', " and /x1a.

This function must always (with few exceptions) be used to make data safe before sending a query to MySQL.

Example #1 An example SQL Injection Attack

<?php
// Query database to check if there are any matching users
$query = "SELECT * FROM users WHERE user='{$_POST['username']}' AND password='{$_POST['password']}'";
mysql_query($query);

// We didn't check $_POST['password'], it could be anything the user wanted! For example:
$_POST['username'] = 'aidan';
$_POST['password'] = "' OR ''='";

// This means the query sent to MySQL would be:
echo $query;
?>
The query sent to MySQL:

SELECT * FROM users WHERE user='aidan' AND password='' OR ''=''

This would allow anyone to log in without a valid password.

Example #2 A "Best Practice" query

Using mysql_real_escape_string() around each variable prevents SQL Injection. This example demonstrates the "best practice" method for querying a database, independent of the Magic Quotes setting.

<?php

if (isset($_POST['product_name']) && isset($_POST['product_description']) && isset($_POST['user_id'])) {

// Connect

$link = mysql_connect('mysql_host', 'mysql_user', 'mysql_password');

if(!is_resource($link)) {

echo "Failed to connect to the server/n";

// ... log the error properly

} else {

// Reverse magic_quotes_gpc/magic_quotes_sybase effects on those vars if ON.

if(get_magic_quotes_gpc()) {

$product_name = stripslashes($_POST['product_name']);

$product_description = stripslashes($_POST['product_description']);

} else {

$product_name = $_POST['product_name'];

$product_description = $_POST['product_description'];

}

// Make a safe query

$query = sprintf("INSERT INTO products (`name`, `description`, `user_id`) VALUES ('%s', '%s', %d)",

mysql_real_escape_string($product_name, $link),

mysql_real_escape_string($product_description, $link),

$_POST['user_id']);

mysql_query($query, $link);

if (mysql_affected_rows($link) > 0) {

echo "Product inserted/n";

}

}

} else {

echo "Fill the form properly/n";

}

?>

The query will now execute correctly, and SQL Injection attacks will not work.

9. strtr
(PHP 4, PHP 5)

strtr — Translate certain characters

Description

string strtr ( string $str , string $from , string $to )
string strtr ( string $str , array $replace_pairs )
This function returns a copy of str , translating all occurrences of each character in from to the corresponding character in to .

If from and to are different lengths, the extra characters in the longer of the two are ignored.

Example strtr() example with two arguments

<?php
$trans = array("hello" => "hi", "hi" => "hello");
echo strtr("hi all, I said hello", $trans);
?>
The above example will output:

hello all, I said hi

See also:

str_replace()
str_ireplace()
ereg()
eregi()
ereg_replace()
eregi_replace()
preg_replace()

10. realpath
(PHP 4, PHP 5)

realpath — Returns canonicalized absolute pathname

Description

string realpath ( string $path )
realpath() expands all symbolic links and resolves references to '/./', '/../' and extra '/' characters in the input path . and return the canonicalized absolute pathname.

Example #1 realpath() example

<?php
chdir('/var/www/');
echo realpath('./../../etc/passwd');
?>
The above example will output:

/etc/passwd

Example #2 realpath() on Windows

On windows realpath() will change unix style paths to windows style.

<?php
echo realpath('/windows/system32');
?>
The above example will output:

C:/WINDOWS/System32

See Also[/b]

[/b]basename()
dirname()
pathinfo()