PHP Strings and Pattern: Length, transforming, array as string

Determining the Length of a String

The strlen() function is used to determine the length, in bytes, of a string. Note that strlen(), like most string functions, is bin ary-safe. This means that all characters in the string are counted, regardless of their value. (In some languages (notably C), some functions are designed to work with “zero-terminated” strings, where the NUL character is used to signal the end of a string. This causes problems when dealing with binary objects, since bytes with a value of zero are quite common; luckily, most PHP functions are capable of handling binary data without any problem.)

Transforming a String

The strtr() function can be used to translate certain characters of a string into other characters—it is often used as an aid in the practice known as transliteration to transform certain accented characters that cannot appear, for example, in URLs or e-mail address into the equivalent unaccented versions:

// Single character version

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

// Multiple-character version

$subst = array (

’1’ => ’one’,

’2’ => ’two’,

);

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

Using Strings as Arrays

You can access the individual characters of a string as if they were members of an array. For example:

$string = ’abcdef’;

echo $string[1]; // Outputs ’b’

This approach can be very handy when you need to scan a string one character at a time:

$s = ’abcdef’;

for ($i = 0; $i < strlen ($s); $i++) {

if ($s[$i] > ’c’) {

echo $s[$i];

}

}

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

Comparison is, perhaps, one of the most common operations performed on strings. At times, PHP’s type-juggling mechanisms also make it the most maddening—particularly because strings that can be interpreted as numbers are often transparently converted to their numeric equivalent. Consider, for example, the following code:

$string = ’123aa’;

if ($string == 123) {

// The string equals 123

}

You’d expect this comparison to return false, since the two operands are most definitely not the same. However, PHP first transparently converts the contents of $string to the integer 123, thus making the comparison true. Naturally, the best way to avoid this problem is to use the identity operator === whenever you are performing a comparison that could potentially lead to type-juggling problems.

In addition to comparison operators, you can also use the specialized functions strcmp() and strcasecmp() to match strings. These are identical, with the exception that the former is case-sensitive, while the latter is not. In both cases, a result of zero indicates that the two strings passed to the function are equal:

$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

}

A further variant of strcasecmp(), strcasencmp() allows you to only test a given number of characters inside two strings. For example:

$s1 = ’abcd1234’;

$s2 = ’abcd5678’;

// Compare the first four characters

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

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