Strings and Patterns

String Basics

String Basics

hex and octal notation to display an asterisk:

echo "\x2a";

echo "\052";

Variable Interpolation

$who = "World";

echo "Hello $who\n"; // Shows "Hello World" followed by a newline

echo ’Hello $who\n’; // Shows "Hello $who\n"

Variable Interpolation, cont’d

$me = ’Davey’;

$names = array (’Smith’, ’Jones’, ’Jackson’);

echo "There cannot be more than two {$me}s!";

echo "Citation: {$names[1]}[1987]";

The Heredoc Syntax

Used to declare complex strings

Easier to declare strings that include many double-quote characters

$who = "World";

echo <<<TEXT

So I said, "Hello $who"

TEXT;

String Length

The strlen() function is used to determine the length, in bytes, of a string

binary-safe: all characters in the string are counted, regardless of their value

String Transform

The strtr() function can be used to translate certain characters of a string into other characters

// Single character version

echo strtr (’abc’, ’a’, ’1’); // Outputs 1bc

// Multiple-character version

$subst = array (

’1’ => ’one’,

’2’ => ’two’,

);

echo strtr (’123’, $subst); // Outputs onetwo3

Strings as Arrays

Individual characters of a string can be accessed as if they were members of an array

$string = ’abcdef’;

echo $string[1]; // Outputs ’b’

Note that string character indices are zero-based - meaning that the first character of an arbitrary string $s has an index of zero, and the last has an index of strlen($s)-1.

Comparing, Searching and Replacing Strings

String Comparison, cont’d

$string = ’123aa’;

if ($string == 123) {

// The string equals 123

}

String Comparison

$str = "Hello World";

if (strcmp($str, "hello world") === 0) {

// We won’t get here, because of case sensitivity

}

if (strcasecmp($str, "hello world") === 0) {

// We will get here, because strcasecmp()

// is case-insensitive

}

String Comparison, cont’d

$s1 = ’abcd1234’;

$s2 = ’abcd5678’;

// Compare the first four characters

echo strncasecmp ($s1, $s2, 4);

String Search

$haystack = "abcdefg";

$needle = ’abc’;

if (strpos ($haystack, $needle) !== false) {

echo ’Found’;

}

String Search, cont’d

$haystack = ’123456123456’;

$needle = ’123’;

echo strpos ($haystack, $needle); // outputs 0

echo strpos ($haystack, $needle, 1); // outputs 6

String Search, cont’d

$haystack = ’123456’;

$needle = ’34’;

echo strstr ($haystack, $needle); // outputs 3456

Note Well

In general, strstr() is slower than strpos()—therefore, you should use the latter if your only goal is to determine whether a certain needle occurs inside the haystack.

Also, note that you cannot force strstr() to start looking for the needle from a given location by passing a third parameter.

String Search, cont’d

// Case-insensitive search

echo stripos(’Hello World’, ’hello’); // outputs zero

echo stristr(’Hello My World’, ’my’); // outputs "My World"

// Reverse search

echo strrpos (’123123’, ’123’); // outputs 3

Matching Against a Mask

$string = ’133445abcdef’;

$mask = ’12345’;

echo strspn ($string, $mask); // Outputs 6

Note Well

The strcspn() function works just like strspn(), but uses a blacklist approach instead—that is, the mask is used to specify which characters are disallowed, and the function returns the length of the initial segment of the string that does not contain any of the characters from the mask.

Matching Against a Mask, cont’d

$string = ’1abc234’;

$mask = ’abc’;

echo strspn ($string, $mask, 1, 4);

Search and Replace Operations

echo str_replace("World", "Reader", "Hello World");

echo str_ireplace("world", "Reader", "Hello World");

Search and Replace, cont’d

echo str_replace(array("Hello", "World"), array("Bonjour", "Monde"), "Hello World");

echo str_replace(array("Hello", "World"), "Bye", "Hello World");

Search and Replace, cont’d

echo substr_replace("Hello World", "Reader", 6);

echo substr_replace("Canned tomatoes are good", "potatoes", 7, 8);

Search and Replace, cont’d

$user = “henry@thinktankesolutions.com";

$name = substr_replace($user, "", strpos($user, ’@’);

echo "Hello " . $name;

Extracting Substrings

$x = ’1234567’;

echo substr ($x, 0, 3); // outputs 123

echo substr ($x, 1, 1); // outputs 2

echo substr ($x, -2); // outputs 67

echo substr ($x, 1); // outputs 234567

echo substr ($x, -2, 1); // outputs 6

Formatting Strings

Formatting Numbers

// Shows 100,001

echo number_format("100000.698");

// Shows 100 000,698

echo number_format("100000.698", 3, ",", " ");

Formatting Currency Values

setlocale(LC_MONETARY, "en_US");

echo money_format(’%.2n’, "100000.698");//$100,000.70

setlocale(LC_MONETARY, "ja_JP.UTF-8");

echo money_format(’%.2n’, "100000.698");//¥100,000.70

Generic Formatting

If you are not handling numbers or currency values, you can use the printf() family of functions to perform arbitrary formatting of a value.

A formatting specifier always starts with a percent symbol and is followed by a type specification token: A sign specifier (a plus or minus symbol) to determine how signed numbers are to be

rendered

A padding specifier that indicates what character should be used to make up the required output length, should the input not be long enough on its own

An alignment specifier that indicates if the output should be left or right aligned

A numeric width specifier that indicates the minimum length of the output

A precision specifier that indicates how many decimal digits should be dis-played for floating-point numbers

Commonly Used Specifiers

b Output an integer as a Binary number.

c Output the character which has the input integer as its ASCII value.

d Output a signed decimal number

e Output a number using scientific notation (e.g., 3.8e+9)

u Output an unsigned decimal number

f Output a locale aware float number

F Output a non-locale aware float number

o Output a number using its Octal representation

s Output a string

x Output a number as hexadecimal with lowercase letters

X Output a number as hexadecimal with uppercase letters

Examples of printf() usage

$n = 123;

$f = 123.45;

$s = "A string";

printf ("%d", $n); // prints 123

printf ("%d", $f); // prints 123

// Prints "The string is A string"

printf ("The string is %s", $s);

// Example with precision

printf ("%3.3f", $f); // prints 123.450

// Complex formatting

function showError($msg, $line, $file)

{

return sprintf("An error occurred in %s on "line %d: %s", $file, $line, $msg);

}

showError ("Invalid deconfibulator", __LINE__, __FILE__);

Parsing Formatted Input

$data = ’123 456 789’;

$format = ’%d %d %d’;

var_dump (sscanf ($data, $format));

Strings and Patterns