PHP 4 offers an output-buffering subsystem that enables you
access to the output of the script, manipulate it, and then do whatever you
desire with the resulting data. One possible use of this feature is to create a
page-caching system.
New Extensions
PHP comes with many new extensions that weren't available
with PHP 3. These extensions include, but are not limited to, the swf, curl,
exif, cybercash, sockets, and ingres_ii extensions.
PEAR
PEAR stands for PHP Extension and Application Repository. The
concept of PEAR is akin to that of Perl's CPAN—it is a repository of PHP classes
and supporting extensions to help you program. For example, the
File_Find class is distributed through PEAR. This class enables you to
map and search different directory trees. More information about PEAR is
available at http://pear.php.net/.
PHP's built-in substr() and substr_replace() functions, which
enable you to read and write parts of the string: <?php
$sub_str = substr ($str, $initial_pos);
$sub_str = substr ($str, $initial_pos, $str_len);
$new_str = substr_replace ($str, $replacement, $initial_pos);
$new_str = substr_replace ($str, $replacement, $initial_pos, $str_len);
?>
PHP treats strings as a basic data
type instead of an array of bytes. Therefore, it is possible for you to use a
function such as substr() or substr_replace() to access and
modify individual characters or portions of strings.
The first argument to substr() is the string on which
you want to operate. The second argument to substr() specifies the
beginning index of the substring you want to access. If the second argument is
positive, the substring will start at that character counting from the beginning
of the string. If the second argument is negative, the substring will start at
that character counting from the end of the string.
Ternary Operator
the ?: conditional to test the value of the user input:
<?php
// If the user has provided a first argument to the program use
// that, otherwise STDIN (php://stdin)
$filename = isset ($argv[1]) ? $argv[1] : "php://stdin";
$fp = @fopen ($filename, 'r')
or die ("Cannot Open $filename for reading");
while (!@feof ($fp)) {
$line = @fgets ($fp, 1024);
print $line;
}
@fclose ($fp);
?>
The preceding code implementing the ternary operator is the
equivalent of the following:
<?php
if (isset ($argv[1])) {
$filename = $argv[1];
} else {
$filename = "php://stdin";
}
?>
However, PHP's ternary operator ( ?:)
greatly reduces the time it takes for programmers to write these statements. Its
syntax is as follows: condition ? do_if_true : do_if_false;
The use of the ternary operator is what is
known as "syntactical sugar"; that is, it is a construct that is not needed, but
is a nice way of beautifying code. None the less, it can be used to replace ugly
if .. else code blocks and improve the readability of your code.
The list() and array() constructs to switch the variables
the list() and array() constructs to switch the variables:
<?php
list ($var1, $var2) = array ($var2, $var1);
?>
In many other languages, you must use a temporary variable,
like so:
<?php
$temp = $var1;
$var1 = $var2;
$var2 = $temp;
?>
However, in PHP, the list() construct does this for
you. The list() construct is used to assign a list of variables
chr() and ord() or sprintf() to convert back and
forth:
<?php
$letter = chr (67); // Upper case C
$ascii_code = ord ($letter); // 67
$letter = sprintf ("%c", $ascii_code); // Upper case C
?>
On the surface, converting ASCII values seems to be a pretty
useless task. When I was a beginning programmer (Perl at the time), I thought
that it was pointless for people even to write these functions and explanations.
However, there are many cases in which you do need to convert back and forth.
To reverse all the words in a string, use a combination of the
preg_split() function and the array_reverse() function:
<?php
function word_reverse ($str) {
return implode ("", array_reverse (preg_split ("/\ s+/", $str)));
}
$str = "A rose by any other name";
$str_reversed = word_reverse ($str);
print $str_reversed;
// Outputs: name other any by rose A
?>
To reverse all the characters in a string, you can use PHP's strrev()
function: <?php
$str = "A rose by any other name";
$chars_reversed = strrev ($str);
print $chars_reversed;
// Outputs: eman rehto yna yb esor A
?>
The word_reverse() function uses the array_reverse() function, which is available
only with PHP.
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