Strings in PHP

In this part of the PHP programming tutorial, we will work with string data in more detail.

Strings are very important data types in computer languages. That is why we dedicate a whole chapter to working with strings in PHP.

String literals

A string literal is the notation for representing a string value within the text of a computer program. In PHP, strings can be created with single quotes, double quotes or using the heredoc or the nowdoc syntax.

literals.php
<?php

$a = "PHP";
$b = 'PERL';

echo $a, $b;

?>

In this code example, we create two strings and assign them to $a and $b variables. We print them with the echo keyword. The first string is created with the double quote delimiters, the second one with single quotes.

The next example will create a string with a heredoc syntax. The heredoc preserves the line breaks and other whitespace (including indentation) in the text. The heredoc is created with <<< followed by a delimiting identifier, followed, starting on the next line, by the text to be quoted, and then closed by the same identifier on its own line. The closing identifier must not be indented. It can only contain alphanumeric characters and underscores, and must start with a non-digit character or underscore.

heredoc.php
<?php

$str = <<<TEXT
"That is just as I intended." Vautrin said. "You know quite well what
you are about. Good, my little eaglet! You are born to command, you
are strong, you stand firm on your feet, you are game! I respect you."
TEXT;

echo $str, "\n";

?>

The example prints an example of a direct speech.

$ php heredoc.php 
"That is just as I intended." Vautrin said. "You know quite well what
you are about. Good, my little eaglet! You are born to command, you
are strong, you stand firm on your feet, you are game! I respect you."

This is the output of the example.

A nowdoc is specified similarly to a heredoc, but no parsing is done inside a nowdoc. A nowdoc is identified with the same <<< sequence used for heredocs, but the identifier which follows is enclosed in single quotes, e.g. <<<'TEXT'.

nowdoc.php
<?php

$str = <<<'TEXT'
Fear is among the greatest obstacles which prevent us from enjoying life 
to its fullest extent. Since of the most commonly held fears among 
people are the fear of heights and the fear of falling from heights. 
Rock climbing is a fantastic way to conquer these fears. 
TEXT;

echo $str, "\n";

?>

The example prints three sentences using the nowdoc syntax.

$ php nowdoc.php 
Fear is among the greatest obstacles which prevent us from enjoying life 
to its fullest extent. Since of the most commonly held fears among 
people are the fear of heights and the fear of falling from heights. 
Rock climbing is a fantastic way to conquer these fears.

This is the output of the nowdoc.php script.

Interpolation

Variables are interpolated in strings enclosed by double quotes.

interpolation.php
<?php

$quantity = 5;

echo "There are $quantity roses in the vase\n";

?>

The $quantity variable is replaced with its value in the string output.

$ php interpolation.php 
There are 5 roses in the vase

This is the output of the interpolation.php script.

Curly braces can be used when the variable name is next to another character.

curlybraces.php
<?php

$quantity = 5;
$item_name = "rose";

echo "There are $quantity {$item_name}s in the vase\n";

?>

Without the curly braces, the PHP interpreter would look for the $item_names variable, which does not exist.

$ php curlybraces.php 
There are 5 roses in the vase

This is the output of the curlybraces.php script.

String concatenation

PHP uses the dot . operator to concatenate strings.

php > echo "PHP " . "language\n";
PHP language

The example concatenates two strings.

php > $a = "Java ";
php > $a .= "language\n";
php > echo $a;
Java language

PHP also supports the .= compound operator.

Escape characters

An escape character is a single character designated to invoke an alternative interpretation on immediately subsequent characters in a character sequence.

php > echo "   bbb\raaa";
aaabbb

The carriage return \r is a control character for end of line return to the beginning of line.

strophe.php
<?php
echo "Incompatible, it don't matter though\n'cos someone's bound to hear my cry\n";
echo "Speak out if you do\nYou're not easy to find\n";
?>

The new line is a control characters which begins a new line of text.

$ php strophe.php 
Incompatible, it don't matter though
'cos someone's bound to hear my cry
Speak out if you do
You're not easy to find

This is the output of the strophe.php script.

php > echo "Towering\tinferno\n";
Towering        inferno

The horizontal tab puts a space between text.

"Johnie's dog"
'Johnie\'s dog'

Single and double quotes can be nested. Or in case we use only single quotes, we can use the backslash to escape the default meaning of a single quote.

backslash.php
<?php

$text = "
\"That is just as I intended.\" Vautrin said. \"You know quite well what
you are about. Good, my little eaglet! You are born to command, you
are strong, you stand firm on your feet, you are game! I respect you.\"
";

echo $text;
?>

In this example, we have a multiline text, which includes direct speech. The double quotes are escaped with the backslash character.

php > $var = 233;
php > echo "$var";
233
php > echo "\$var is $var";
$var is 233

The dollar sign $ has also a special meaning in PHP; it denotes a variable. If a variable is used inside a string, it is interpolated, i.e. the value of the variable is used. To echo a variable name, we escape the $ character \$.

Operations on strings

PHP has a large number of useful useful built-in functions that can be used for working with strings.

echo strlen("Eagle"); # prints 5
echo strtoupper("Eagle"); # prints EAGLE
echo strtolower("Eagle"); # prints eagle

Here we use three functions. The strlen() function returns a number of characters in the string. The strtoupper() converts characters to uppercase letters, and the strtolower() converts characters to lowercase letters.

letters.php
<?php

$sentence = "There are 22 apples";

$alphas = 0;
$digits = 0;
$spaces = 0;

$length = strlen($sentence);

for ($i = 0; $i < $length; $i++) {

    $c = $sentence[$i];
    if (ctype_alpha($c)) $alphas++;
    if (ctype_digit($c)) $digits++;
    if (ctype_space($c)) $spaces++;

}

echo "There are $length characters.\n";
echo "There are $alphas alphabetic characters.\n";
echo "There are $digits digits.\n";
echo "There are $spaces spaces.\n";

?>

In our example, we have a string sentence. We calculate the absolute number of characters, number of alphabetic characters, digits and spaces in the sentence. To do this, we use the following functions: strlen(), ctype_alpha(), ctype_digit(), and ctype_space().

$ php letters.php 
There are 19 characters.
There are 14 alphabetic characters.
There are 2 digits.
There are 3 spaces.

This is the output of the letters.php script.

Next, we cover the substr() function.

echo substr("PHP language", 0, 3); # prints PHP
echo substr("PHP language", -8); # prints language

The function returns a part of a string. The first parameter is the specified string. The second parameter is the start of the substring. The third parameter is optional. It is the length of the returned substring. The default is to the return until the end of the string.

The str_repeat() function repeats a string a specified number of times.

repeat.php
<?php

echo str_repeat("#", 18);
echo "\nProject Neurea\n";
echo "Priority high\n";
echo "Security maximum\n";
echo str_repeat("#", 18);
echo "\n";

?>

We use the str_repeat() function to create two lines of the # character.

$ php repeat.php 
##################
Project Neurea
Priority high
Security maximum
##################

This is the output of the repeat.php script.

In the next example, we will randomly modify a string.

shuffling.php
<?php

$string = "ZetCode";

echo str_shuffle($string), "\n";
echo str_shuffle($string), "\n";
echo str_shuffle($string), "\n";
echo str_shuffle($string), "\n";
echo str_shuffle($string), "\n";
echo str_shuffle($string), "\n";
echo str_shuffle($string), "\n";

?>

The str_shuffle() randomly shuffles a string.

$ php shuffling.php 
ZtCeoed
eodtCZe
toZeeCd
oCdeteZ
edtCZoe
tdeCeoZ
oeZdteC

This is a sample output of the shuffling.php script.

The explode() function is used to split a string into parts. It returns an array of split string parts.

exploding.php
<?php

$nums = "1,2,3,4,5,6,7,8,9,10,11";

$vals = explode(",", $nums);
$len = count($vals);

echo "There are $len numbers in the string\n";

?>

We have integers within a string separated by comma character. We count the number of integers.

$vals = explode(",", $nums);

Here we split the text with the explode() function. The function will cut a string into pieces whenever it finds the dot , character.

$ php exploding.php 
There are 11 numbers in the string

Output of the example.

teams1.php
<?php

echo "Ajax Amsterdam" . " - " . "Inter Milano " . "2:3\n";
echo "Real Madridi" . " - " . "AC Milano " . "3:3\n";
echo "Dortmund" . " - " . "Sparta Praha ". "2:1\n";

?>

We concatenate strings with the dot operator.

$ php teams1.php
Ajax Amsterdam - Inter Milano 2:3
Real Madridi - AC Milano 3:3
Dortmund - Sparta Praha 2:1

The output is not optimal. We will change it so that it looks neater.

teams2.php
<?php

$teams = array( 
      array("Ajax Amsterdam", "Inter Milano"),
      array("Real Madrid", "AC Milano"),
      array("Dortmund", "Sparta Praha")
);

$results = array("2:3", "3:3", "2:1");

$i = 0;

foreach ($teams as $team) {
    echo str_pad($team[0], 14);
    echo str_pad("-", 3, " ", STR_PAD_BOTH);
    echo str_pad($team[1], 14);
    echo str_pad($results[$i], 3, " ", STR_PAD_LEFT);
    echo "\n";
    $i++;
}
?>

We improve the output format with the str_pad() function. It adds a specified string (in our case a space) to the left of the string, to the right or to both sides.

$ php teams2.php 
Ajax Amsterdam - Inter Milano  2:3
Real Madrid    - AC Milano     3:3
Dortmund       - Sparta Praha  2:1

We manage to give a nicer formatted output.

Array of chars

A string in PHP is an array of chars.

array_of_chars.php
<?php

$site = "zetcode.com";

for ($i=0; $i < strlen($site); $i++) {
    $o = ord($site[$i]);
    echo "$site[$i] has ASCII code $o\n";
}

?>

In the example, we iterate through a string and print each character's ASCII code.

$site = "zetcode.com";

A string is defined. It contains eleven characters.

for ($i=0; $i < strlen($site); $i++) {
    $o = ord($site[$i]);
    echo "$site[$i] has ASCII code $o\n";
}

We iterate through the string with the for loop. The size of the string is determined with the strlen() function. The ord() function returns the ASCII value of a character. We use the array index notation to get a character.

$ php array_of_chars.php 
z has ASCII code 122
e has ASCII code 101
t has ASCII code 116
c has ASCII code 99
o has ASCII code 111
d has ASCII code 100
e has ASCII code 101
. has ASCII code 46
c has ASCII code 99
o has ASCII code 111
m has ASCII code 109

This is the output of the array_of_chars.php example.

String formatting

String formatting or string interpolation is dynamic putting of various values into a string.

fruits.php
<?php

printf("There are %d oranges and %d apples in the basket.\n", 12, 32);

?>

We use the %d formatting specifier. The specifier expects an integer value to be passed.

$ php fruits.php 
There are 12 oranges and 32 apples in the basket.

In the next example, we pass a float and a string value.

height.php
<?php

printf("Height: %f %s\n", 172.3, "cm");

?>

The formatting specifier for a float value is %f and for a string %s.

$ php height.php 
Height: 172.300000 cm

We might not like the fact that the number in the previous example has 6 decimal places by default. We can control the number of the decimal places in the formatting specifier.

height2.php
<?php

printf("Height: %.1f %s\n", 172.3, 'cm');

?>

The decimal point followed by an integer controls the number of decimal places. In our case, the number has exactly one decimal place.

$ php height2.php 
Height: 172.3 cm

The following example shows other formatting options.

formatting.php
<?php

# hexadecimal
printf("%x\n", 300);

# octal
printf("%o\n", 300);

# scientific
printf("%e\n", 300000);

?>

The first format works with hexadecimal numbers. The x character formats the number in hexadecimal notation. The o character shows the number in octal format. The e character shows the number in scientific format.

$ php formatting.php 
12c
454
3.000000e+5

The next example prints three columns of numbers.

columns.php
<?php

foreach (range(1,11) as $num) {
    echo $num , " ", $num*$num, " ",
         $num*$num*$num, "\n";
}

?>

The numbers are left justified and the output is not neat.

$ php columns.php 
1 1 1
2 4 8
3 9 27
4 16 64
5 25 125
6 36 216
7 49 343
8 64 512
9 81 729
10 100 1000
11 121 1331

To correct this, we use the width specifier. The width specifier defines the minimal width of the object. If the object is smaller than the width, it is filled with spaces.

columns2.php
<?php

foreach (range(1,11) as $num) {
    printf("%2d %3d %4d\n", $num, $num*$num, $num*$num*$num);
}

?>

Now the output looks OK. Number 2 says that the first column will be 2 characters wide.

$ php columns2.php 
 1   1    1
 2   4    8
 3   9   27
 4  16   64
 5  25  125
 6  36  216
 7  49  343
 8  64  512
 9  81  729
10 100 1000
11 121 1331

This part of the PHP tutorial covered strings.