9 Useful PHP Functions and Features You Need to Know

转载自：http://net.tutsplus.com/tutorials/php/9-useful-php-functions-and-features-you-need-to-know/

1.

Functions with Arbitrary Number of Arguments

You may already know that PHP allows you to define functions with
optional arguments. But there is also a method for allowing completely
arbitrary number of function arguments.

First, here is an example with just optional arguments:

// function with 2 optional arguments
function foo($arg1 = '', $arg2 = '') {

echo "arg1: $arg1/n";
echo "arg2: $arg2/n";

}

foo('hello','world');
/* prints:
arg1: hello
arg2: world
*/

foo();
/* prints:
arg1:
arg2:
*/

Now, let’s see how we can build a function that accepts any number of arguments. This time we are going to utilize func_get_args()

:

// yes, the argument list can be empty
function foo() {

// returns an array of all passed arguments
$args = func_get_args();

foreach ($args as $k => $v) {
echo "arg".($k+1).": $v/n";
}

}

foo();
/* prints nothing */

foo('hello');
/* prints
arg1: hello
*/

foo('hello', 'world', 'again');
/* prints
arg1: hello
arg2: world
arg3: again
*/

2.

Using Glob() to Find Files

Many PHP functions have long and descriptive names. However it may be hard to tell what a function named glob()

does unless you are already familiar with that term from elsewhere.

Think of it like a more capable version of the scandir()

function. It can let you search for files by using patterns.

// get all php files
$files = glob('*.php');

print_r($files);
/* output looks like:
Array
(
[0] => phptest.php
[1] => pi.php
[2] => post_output.php
[3] => test.php
)
*/

You can fetch multiple file types like this:

// get all php files AND txt files
$files = glob('*.{php,txt}', GLOB_BRACE);

print_r($files);
/* output looks like:
Array
(
[0] => phptest.php
[1] => pi.php
[2] => post_output.php
[3] => test.php
[4] => log.txt
[5] => test.txt
)
*/

Note that the files can actually be returned with a path, depending on your query:

$files = glob('../images/a*.jpg');

print_r($files);
/* output looks like:
Array
(
[0] => ../images/apple.jpg
[1] => ../images/art.jpg
)
*/

If you want to get the full path to each file, you can just call the realpath()

function on the returned values:

$files = glob('../images/a*.jpg');

// applies the function to each array element
$files = array_map('realpath',$files);

print_r($files);
/* output looks like:
Array
(
[0] => C:/wamp/www/images/apple.jpg
[1] => C:/wamp/www/images/art.jpg
)
*/

3.

Memory Usage Information

By observing the memory usage of your scripts, you may be able optimize your code better.

PHP has a garbage collector and a pretty complex memory manager. The
amount of memory being used by your script. can go up and down during
the execution of a script. To get the current memory usage, we can use
the memory_get_usage()

function, and to get the highest amount of memory used at any point, we can use the memory_get_peak_usage()

function.

echo "Initial: ".memory_get_usage()." bytes /n";
/* prints
Initial: 361400 bytes
*/

// let's use up some memory
for ($i = 0; $i < 100000; $i++) {
$array []= md5($i);
}

// let's remove half of the array
for ($i = 0; $i < 100000; $i++) {
unset($array[$i]);
}

echo "Final: ".memory_get_usage()." bytes /n";
/* prints
Final: 885912 bytes
*/

echo "Peak: ".memory_get_peak_usage()." bytes /n";
/* prints
Peak: 13687072 bytes
*/

4.

CPU Usage Information

For this, we are going to utilize the getrusage()

function. Keep in mind that this is not available on Windows platforms.

print_r(getrusage());
/* prints
Array
(
[ru_oublock] => 0
[ru_inblock] => 0
[ru_msgsnd] => 2
[ru_msgrcv] => 3
[ru_maxrss] => 12692
[ru_ixrss] => 764
[ru_idrss] => 3864
[ru_minflt] => 94
[ru_majflt] => 0
[ru_nsignals] => 1
[ru_nvcsw] => 67
[ru_nivcsw] => 4
[ru_nswap] => 0
[ru_utime.tv_usec] => 0
[ru_utime.tv_sec] => 0
[ru_stime.tv_usec] => 6269
[ru_stime.tv_sec] => 0
)

*/

That may look a bit cryptic unless you already have a system
administration background. Here is the explanation of each value (you
don't need to memorize these):

ru_oublock:

block output operations

ru_inblock:

block input operations

ru_msgsnd:

messages sent

ru_msgrcv:

messages received

ru_maxrss:

maximum resident set size

ru_ixrss:

integral shared memory size

ru_idrss:

integral unshared data size

ru_minflt:

page reclaims

ru_majflt:

page faults

ru_nsignals:

signals received

ru_nvcsw:

voluntary context switches

ru_nivcsw:

involuntary context switches

ru_nswap:

swaps

ru_utime.tv_usec:

user time used (microseconds)

ru_utime.tv_sec:

user time used (seconds)

ru_stime.tv_usec:

system time used (microseconds)

ru_stime.tv_sec:

system time used (seconds)

To see how much CPU power the script has consumed, we need to look at
the 'user time' and 'system time' values. The seconds and microseconds
portions are provided separately by default. You can divide the
microseconds value by 1 million, and add it to the seconds value, to get
the total seconds as a decimal number.

Let's see an example:

// sleep for 3 seconds (non-busy)
sleep(3);

$data = getrusage();
echo "User time: ".
($data['ru_utime.tv_sec'] +
$data['ru_utime.tv_usec'] / 1000000);
echo "System time: ".
($data['ru_stime.tv_sec'] +
$data['ru_stime.tv_usec'] / 1000000);

/* prints
User time: 0.011552
System time: 0
*/

Even though the script took about 3 seconds to run, the CPU usage was
very very low. Because during the sleep operation, the script actually
does not consume CPU resources. There are many other tasks that may take
real time, but may not use CPU time, like waiting for disk operations.
So as you see, the CPU usage and the actual length of the runtime are
not always the same.

Here is another example:

// loop 10 million times (busy)
for($i=0;$i<10000000;$i++) {

}

$data = getrusage();
echo "User time: ".
($data['ru_utime.tv_sec'] +
$data['ru_utime.tv_usec'] / 1000000);
echo "System time: ".
($data['ru_stime.tv_sec'] +
$data['ru_stime.tv_usec'] / 1000000);

/* prints
User time: 1.424592
System time: 0.004204
*/

That took about 1.4 seconds of CPU time, almost all of which was user time, since there were no system calls.

System Time is the amount of time the CPU spends performing system
calls for the kernel on the program's behalf. Here is an example of
that:

$start = microtime(true);
// keep calling microtime for about 3 seconds
while(microtime(true) - $start < 3) {

}

$data = getrusage();
echo "User time: ".
($data['ru_utime.tv_sec'] +
$data['ru_utime.tv_usec'] / 1000000);
echo "System time: ".
($data['ru_stime.tv_sec'] +
$data['ru_stime.tv_usec'] / 1000000);

/* prints
User time: 1.088171
System time: 1.675315
*/

Now we have quite a bit of system time usage. This is because the script
calls the microtime() function many times, which performs a request
through the operating system to fetch the time.

Also you may notice the numbers do not quite add up to 3 seconds. This
is because there were probably other processes on the server as well,
and the script was not using 100% CPU for the whole duration of the 3
seconds.

5.

Magic Constants

PHP provides useful magic constants

for fetching the current line number (

__LINE__

), file path (

__FILE__

), directory path (

__DIR__

), function name (

__FUNCTION__

), class name (

__CLASS__

), method name (__METHOD__) and namespace (

__NAMESPACE__

).

We are not going to cover each one of these in this article, but I will show you a few use cases.

When including other scripts, it is a good idea to utilize the

__FILE__

constant (or also

__DIR__

, as of PHP 5.3):

// this is relative to the loaded script's path
// it may cause problems when running scripts from different directories
require_once('config/database.php');

// this is always relative to this file's path
// no matter where it was included from
require_once(dirname(__FILE__) . '/config/database.php');

Using

__LINE__

makes debugging easier. You can track down the line numbers:

// some code
// ...
my_debug("some debug message", __LINE__);
/* prints
Line 4: some debug message
*/

// some more code
// ...
my_debug("another debug message", __LINE__);
/* prints
Line 11: another debug message
*/

function my_debug($msg, $line) {
echo "Line $line: $msg/n";
}

6.

Generating Unique ID's

There may be situations where you need to generate a unique string. I have seen many people use the

md5()

function for this, even though it's not exactly meant for this purpose:

// generate unique string
echo md5(time() . mt_rand(1,1000000));

There is actually a PHP function named uniqid()

that is meant to be used for this.

// generate unique string
echo uniqid();
/* prints
4bd67c947233e
*/

// generate another unique string
echo uniqid();
/* prints
4bd67c9472340
*/

You may notice that even though the strings are unique, they seem
similar for the first several characters. This is because the generated
string is related to the server time. This actually has a nice side
effect, as every new generated id comes later in alphabetical order, so
they can be sorted.

To reduce the chances of getting a duplicate, you can pass a prefix, or the second parameter to increase entropy:

// with prefix
echo uniqid('foo_');
/* prints
foo_4bd67d6cd8b8f
*/

// with more entropy
echo uniqid('',true);
/* prints
4bd67d6cd8b926.12135106
*/

// both
echo uniqid('bar_',true);
/* prints
bar_4bd67da367b650.43684647
*/

This function will generate shorter strings than

md5()

, which will also save you some space.

7.

Serialization

Have you ever needed to store a complex variable in a database or a
text file? You do not have to come up with a fancy solution to convert
your arrays or objects into formatted strings, as PHP already has
functions for this purpose.

There are two popular methods of serializing variables. Here is an example that uses the serialize()

and unserialize()

:

// a complex array
$myvar = array(
'hello',
42,
array(1,'two'),
'apple'
);

// convert to a string
$string = serialize($myvar);

echo $string;
/* prints
a:4:{i:0;s:5:"hello";i:1;i:42;i:2;a:2:{i:0;i:1;i:1;s:3:"two";}i:3;s:5:"apple";}
*/

// you can reproduce the original variable
$newvar = unserialize($string);

print_r($newvar);
/* prints
Array
(
[0] => hello
[1] => 42
[2] => Array
(
[0] => 1
[1] => two
)

[3] => apple
)
*/

This was the native PHP serialization method. However, since JSON has
become so popular in recent years, they decided to add support for it in
PHP 5.2. Now you can use the

json_encode()

and

json_decode()

functions as well:

// a complex array
$myvar = array(
'hello',
42,
array(1,'two'),
'apple'
);

// convert to a string
$string = json_encode($myvar);

echo $string;
/* prints
["hello",42,[1,"two"],"apple"]
*/

// you can reproduce the original variable
$newvar = json_decode($string);

print_r($newvar);
/* prints
Array
(
[0] => hello
[1] => 42
[2] => Array
(
[0] => 1
[1] => two
)

[3] => apple
)
*/

It is more compact, and best of all, compatible with javascript and many
other languages. However, for complex objects, some information may be
lost.

8.

Compressing Strings

When talking about compression, we usually think about files, such as
ZIP archives. It is possible to compress long strings in PHP, without
involving any archive files.

In the following example we are going to utilize the gzcompress()

and gzuncompress()

functions:

$string =
"Lorem ipsum dolor sit amet, consectetur
adipiscing elit. Nunc ut elit id mi ultricies
adipiscing. Nulla facilisi. Praesent pulvinar,
pien vel feugiat vestibulum, nulla dui pretium orci,
non ultricies elit lacus quis ante. Lorem ipsum dolor
sit amet, consectetur adipiscing elit. Aliquam
pretium ullamcorper urna quis iaculis. Etiam ac massa
sed turpis tempor luctus. Curabitur sed nibh eu elit
mollis congue. Praesent ipsum diam, consectetur vitae
ornare a, aliquam a nunc. In id magna pellentesque
tellus posuere adipiscing. Sed non mi metus, at lacinia
augue. Sed magna nisi, ornare in mollis in, mollis
sed nunc. Etiam at justo in leo congue mollis.
Nullam in neque eget metus hendrerit scelerisque
eu non enim. Ut malesuada lacus eu nulla bibendum
id euismod urna sodales. ";

$compressed = gzcompress($string);

echo "Original size: ". strlen($string)."/n";
/* prints
Original size: 800
*/

echo "Compressed size: ". strlen($compressed)."/n";
/* prints
Compressed size: 418
*/

// getting it back
$original = gzuncompress($compressed);

We were able to achive almost 50% size reduction. Also the functions gzencode()

and gzdecode()

achive similar results, by using a different compression algorithm.

9.

Register Shutdown Function

There is a function called register_shutdown_function()

, which will let you execute some code right before the script finishes running.

Imagine that you want to capture some benchmark statistics at the end of your script execution, such as how long it took to run:

// capture the start time
$start_time = microtime(true);

// do some stuff
// ...

// display how long the script took
echo "execution took: ".
(microtime(true) - $start_time).
" seconds.";

At first this may seem trivial. You just add the code to the very
bottom of the script and it runs before it finishes. However, if you
ever call the exit()

function, that code will never run. Also, if there is a fatal error, or
if the script is terminated by the user (by pressing the Stop button in
the browser), again it may not run.

When you use register_shutdown_function(), your code will execute no matter why the script has stopped running:

$start_time = microtime(true);

register_shutdown_function('my_shutdown');

// do some stuff
// ...

function my_shutdown() {
global $start_time;

echo "execution took: ".
(microtime(true) - $start_time).
" seconds.";
}

Conclusion

Are you aware of any other PHP features that are not widely known but
can be quite useful? Please share with us in the comments. And thank
you for reading!