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

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 '&lt;'
• '>' (greater than) becomes '&gt;'

Example #1 htmlspecialchars() example

 <?php
$new = htmlspecialchars("<a href='test'>Test</a>", ENT_QUOTES);
echo $new; // &lt;a href=&#039;test&#039;&gt;Test&lt;/a&gt;
?>

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 -&gt; &quot;</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 -> &quot;</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 &lt;b&gt;bold&lt;/b&gt;
echo htmlentities($str);

// Outputs: A &#039;quote&#039; is &lt;b&gt;bold&lt;/b&gt;
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 &quot;walk&quot; the &lt;b&gt;dog&lt;/b&gt; 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

addcslashes()
stripcslashes()
get_magic_quotes_gpc()

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 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.

1.  <?php
3. if (isset($_POST['product_name']) && isset($_POST['product_description']) && isset($_POST['user_id'])) {
4.    // Connect
6.    $link = mysql_connect('mysql_host', 'mysql_user', 'mysql_password');
8.    if(!is_resource($link)) {
10.        echo "Failed to connect to the server/n";
11.        // ... log the error properly
13.    } else {
14.        
15.        // Reverse magic_quotes_gpc/magic_quotes_sybase effects on those vars if ON.
17.        if(get_magic_quotes_gpc()) {
18.            $product_name        = stripslashes($_POST['product_name']);
19.            $product_description = stripslashes($_POST['product_description']);
20.        } else {
21.            $product_name        = $_POST['product_name'];
22.            $product_description = $_POST['product_description'];
23.        }
25.        // Make a safe query
26.        $query = sprintf("INSERT INTO products (`name`, `description`, `user_id`) VALUES ('%s', '%s', %d)",
27.                    mysql_real_escape_string($product_name, $link),
28.                    mysql_real_escape_string($product_description, $link),
29.                    $_POST['user_id']);
31.        mysql_query($query, $link);
33.        if (mysql_affected_rows($link) > 0) {
34.            echo "Product inserted/n";
35.        }
36.    }
37. } else {
38.    echo "Fill the form properly/n";
39. }
40. ?>

 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

basename()
dirname()
pathinfo()