PHP by Book

Here’s how PHP developer declare a string, which is something very common in any programming language.

$my_var = 'hello world';
// or
$my_var = "hello world";

PHP Tricks

What if you do the following:

echo hello;

That appears to be correct … Well, it’s not absolutely correct. You’ll be “noticed”.

// Notice: Use of undefined constant hello
echo hello;

However if you disable error reporting, the code will be completely fine.

error_reporting(0);

// no problem now
echo hello;

Variations

What follows from the thing above is that you can use strings without quotes:

// hello
echo hello;

// hello world (concatenated)
echo hello . ' world';

// helloworld
echo hello . world;

However you can’t have spaces and most of the “special” symbols.

// syntax error
echo hello world;

// syntax error
echo hello!;

Final Words

Although you can do this in PHP, that is completely wrong. The code becomes more difficult to read and understand. In the second place you can miss a $ sign in front of a variable declaration and thus the PHP interpreter will assume this is a string. So disable error reporting isn’t so great sometimes.

String matching is something crucial for database development and text processing software. Fortunately every modern programming language and library is full of functions for string processing that help us in our everyday work. However is great to understand their principles.

String algorithms can be mainly divided into several categories. One of these categories is string matching.

When we come to string matching the most basic approach is what is known as brute force, which means just to check every single character from the text to match against the pattern. In general we have a text and a pattern (most commonly shorter than the text). What we need to do is to answer the question whether this pattern appears into the text.

Overview

The principles of brute force string matching are quite simple. We must check for a match between the first characters of the pattern with the first character of the text as on the picture bellow.

In case they match we move forward the second character of the pattern comparing it with the “next” character of the text, as on the picture bellow.

Just because we have found a match between the first character from the pattern with some character of the text, doesn’t mean that the pattern appears in the text. We must move forward to see whether the full pattern is contained into the text.

Implementation

Implementation of brute force string matching is easy and here we can see a short PHP example. The bad news is that naturally this algorithm is quite slow.

function sub_string($pattern, $subject) 
{
	$n = strlen($subject);
	$m = strlen($pattern);
	
	for ($i = 0; i < $n-$m; $i++) {
		$j = 0;
		while ($j < $m && $subject[$i+$j] == $pattern[$j]) {
			$j++;
		}
		if ($j == $m) return $i;
	}
	return -1;
}

echo sub_string('o wo', 'hello world!');

Complexity

As I said this algorithm is slow. Actually every algorithm that contains “brute force” in its name is slow, but to show how slow is string matching I can say that its complexity is O(n.m). Here n is the length of the text, while m is the length of the pattern.

In case we fix the length of the text and test against variable length of the pattern, again we get rapidly growing function.

Application

Brute force string matching can be very ineffective, but it can also be very handy in some cases. Just like the sequential search.

It can be very useful ...

1. Doesn't require pre-processing of the text - Indeed if we search the text only once we don't need to pre-process it. Most of the algorithms for string matching need to build an index of the text in order to search quickly. This is great when you've to search more than once into a text, but if you do only once, perhaps (for short texts) brute force matching is great!
2. Doesn't require additional space - Because brute force matching doesn't need pre-processing it also doesn't require more space, which is one cool feature of this algorithm
3. Can be quite effective for short texts and patterns

It can be ineffective ...

1. If we search more than once the text - As I said in the previous section if you perform the search more than once it's perhaps better to use another string matching algorithm that builds an index and it's faster.
2. It's slow - In general brute force algorithms are slow and brute force matching isn't an exception.

Final Words

String matching is something very special in software development and it is used in various cases, so every developer must be familiar with this topic.

1. What will be the output of the following code?

echo date('Y-m-d', strtotime('-1 month ago'));

• Error
• One month ago from the current date and time
• One month in the future from the current date and time correct answer (ref)

2. Is it possible to extend an interface with an abstract class?

• Yes correct answer (ref)
• No

3. What is the output of the following code?

$arr = array(1 => 10, "1" => 20); 
echo count($arr);

• Error
• 0
• 1 correct answer (ref)
• 2

4. What is the output of the following code?

$str = "hello world"; echo $str{1};

• An error
• h
• e correct answer (ref)
• ello world

5. What is the output of the following code?

$str = "foo Bar"; 
echo ucwords($str);

• Foo bar
• Foo Bar correct answer (ref)
• FOO BAR
• foo bar

$str = 'hello world';
echo substr($str, 0, 1); // outputs "h"

But here’s something better and cleaner.

echo $str{0}; // outputs "h"

This code chunk return the first character of $str, but it can be used with the same success for any other character of the string. In my opinion this is more cleaner and its really syntactically self documented.

This approach can be useful when trying to check whether the first symbol for instance is “?” or “/”.

The Route from $_GET to String

The global arrays in PHP contain request parameters. Either GET or POST. As you know if the page address is something like:

http://www.example.com/index.php?a=b&key=value

This means that you pass to the index.php file two parameters – “a” and “key” with their values: “b” and “value”. Now in this case you can dump the $_GET global array somewhere in index.php and you’ll receive something like this.

array(
	"a"   => "b",
	"key" => "value",
);

This is however pseudocode, but in fact $_GET will be very similar to this sample array.

$_GET to String

Very often when a developer need to process the $_GET array to a string, which means generating again the query string from $_GET, he often comes to some operation like this one.

$queryString = '';
foreach ($_GET as $key => $value) {
	$queryString .= $key . '=' . $value . '&';
}

However this will result in something quite ugly like a=b&key=value& which comes with a trailing & at the end of the string.

There is however another approach – using an array.

$queryString = array();
foreach ($_GET as $key => $value) {
	$queryString[] = $key . '=' . $value;
}
$queryString = implode('&', $queryString);

But that invokes one function more and this is still not the most elegant solution. As I said at the beginning PHP is full of useful functions and here comes the http_build_query.

http_build_query

This is exactly what you need. As it name describe you can build the query string even by using a different from & separator.

$queryString = http_build_query($_GET, '', '|');

Thus $queryString will contain a=b|key=value and at least the code will look pritier.

You should know that in JavaScript you cannot simply write a multilined code chunk, i.e. something like this:

var str = 'hello
world';

This will result in an error, which can be a problem when you deal with large strings. Imagine a string containing some HTML that should be injected via innerHTML. Now one possible solution is to concatenate two or more strings, by splitting the initial string.

var str = 'hello'
        + 'world';

Howerver this solution result in some additional operations like concatenation. It can be very nice if there was something like the PHP multiline string format.

The PHP Example

In PHP you have the same use case with strings. You can have a string concatenated over multiple lines, but you cannot split lines like so:

// the following line is wrong
$str = 'hello
world'; 

// a possible solution to the line above is
$str = 'hello'
     . 'world';
// which is very similar to the js solution in the second example

// ... but in PHP there is the so called HEREDOC
$str = <<
The heredoc gives us the power to write multiline strings. 
The JavaScript Trick
Actually in JavaScript there is something that's exactly what Heredoc is meant to be for PHP. Take a look at the last example:
var text = <>
this 

is
my
multi-line
text
.toString();

document.body.innerHTML = text;

Thus you can write multiline strings in the JavaScript code.

Related posts:

Powerful PHP: Less Known String Manipulation 
JavaScript Flexibility – Regex match() 
Flexible JavaScript – Splitting Strings 
Flexible JavaScript – Replace in a String 


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Related posts:

Powerful PHP: Less Known String Manipulation 
You think you know PHP. Quiz Results! 
Strict types in Zend Framework and in PHP 
PHP: Fetch $_GET as String with http_build_query() 


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The Task
First of all what we’d like to achieve? The task is to convert a string, most of the cases single word, by capitalize the first letter. In my case I’ve the world countries names all lower cased, while I need them with first letter capitalized. In example “united states” must become “United States”, but not “United states” or “UNITED STATES”. So here began the journey into PHP string functions, especially those for capitalization!
1. ucwords
The first thing you find in the PHP Manual is the ucwords function. It changes the first letter to a capital letter, but it does not do the job. Why? Well let me show you an example.
$str1 = 'foo bar';
$str2 = 'Foo bar';
$str3 = 'FOO BAR';
$str4 = 'фуу бар';

echo ucwords($str1); // Foo Bar
echo ucwords($str2); // Foo Bar
echo ucwords($str3); // FOO BAR
echo ucwords($str4); // фуу бар

Here we have four strings. A lower cased, an upper cased, a mixed cased and … a lower cased Cyrillic string. First of all the main reason why ucwords doesn’t fit here is because of the Cyrillic string. Whatever non-Latin string you have you can forget about capitalization. However the other strings conversions are also interesting. Take a look at the third string! Here the string remains “FOO BAR” instead of going “Foo Bar”, which simply means that this function only looks, and hopefully changes, the first letter.
So here we have two questions. How can we overcome the Cyrillic problem and how to “normalize” the UPPER CASE string?
2. ucfirst
This is another useful function in PHP. ucfirst as you may guess from its name converts a string by only changing its first letter. So “Foo bar” will remain “Foo bar”, while with ucwords it has become “Foo Bar”. Let’s see what this function does:
$str1 = 'foo bar';
$str2 = 'Foo bar';
$str3 = 'FOO BAR';
$str4 = 'фуу бар';

echo ucfirst($str1); // Foo bar
echo ucfirst($str2); // Foo bar
echo ucfirst($str3); // FOO BAR
echo ucfirst($str4); // фуу бар

Here even the first string has only one capital letter – “foo bar” became “Foo bar”, and yet again we’ve the Cyrillic string unchanged. It simply doesn’t help us here!
3. mb_convert_case
As a PHP developer you know what the “mb_” prefix means – multibyte. This is quite useful. You can convert the string whatever the encoding is, so perhaps we can overcome the Cyrillic problem. But before proceeding to tests, let’s take a look at the parameters of this function.
The first thing to note here is that mb_convert_case doesn’t contain the case in its name – upper or lower. There’s a second parameter, after the first which is the string itself, who setups that. Note that here you don’t have the typical camel case or capitals parameter name, but MB_CASE_TITLE (as you know in English the title is always capitalized):
echo mb_convert_case($str, MB_CASE_TITLE, ...

And a third one which specifies the encoding:
echo mb_convert_case($str, MB_CASE_TITLE, 'utf-8')

Now let’s see what we can achieve with it:
$str1 = 'foo bar';
$str2 = 'Foo bar';
$str3 = 'FOO BAR';
$str4 = 'фуу бар';

echo mb_convert_case($str1, MB_CASE_TITLE, 'utf-8'); // Foo Bar
echo mb_convert_case($str2, MB_CASE_TITLE, 'utf-8'); // Foo Bar
echo mb_convert_case($str3, MB_CASE_TITLE, 'utf-8'); // Foo Bar
echo mb_convert_case($str4, MB_CASE_TITLE, 'utf-8'); // Фуу Бар

As you can see now the Cyrillic problem doesn’t exists and mb_convert_case is intelligent enough to change “FOO BAR” into “Foo Bar” – as I said this is the English style titling. That is by no means the solution when you deal with capitalization with different encoding.
However there is another approach to overcome the all UPPER CASE conversion problem. A possible solution is to convert the string first to a lower case string.
4. strtolower
strtolower is very useful PHP string function and perhaps any PHP developer has used it at least once. But yet again – it does not do the job. Again because of the encoding problem.
echo strtolower('ФУУ БАР'); // #*&$(#*%#

As you can see the Cyrillic string cannot be lower cased! Let’s search again into the “mb_” universe.
5. mb_strtolower
This is the function. Again you’ve to specify the encoding:
echo mb_strtolower('ФУУ БАР', 'utf-8')

Conclusion
It doesn’t matter whether you’re native English speaker or not. Most of the web sites are multilingual and you cannot be sure what happens when you convert strings in Alphabets different from the Latin. Thus be careful even when everything seems to be OK with Latin string tests.

Related posts:

Powerful PHP: Less Known String Manipulation 
You think you know PHP. Quiz Results! 
Strict types in Zend Framework and in PHP 
PHP: Fetch $_GET as String with http_build_query() 


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