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PHP Strings and Substrings

PHP provides library functions to find and extract substrings from source strings.

Extracting Substrings

The substr() function returns a substring from a string. The function accepts as arguments the source string and the start position counted from zero at the beginning of the string.

It also accepts an optional length argument to determine how many characters to return.

Examples of substr()

<?php
    $name = "Georgina";

    // This prints out gina
    echo (substr ($name, 4));

    // This prints out Georgi
    echo (substr ($name, 0, 6));
?>

If a negative start argument is passed then the start point is counted from the end of the source string.

If a negative length argument is passed then this is treated as the end point, counted from the end of the source string.

Examples of substr() With Negative Arguments

<?php
    $name = "Georgina";

    // This prints out orgina
    echo (substr ($name, -6));

    // This prints out org
    echo (substr ($name, -6, -3));
?>

Finding the Position of a Substring

The strpos() function returns the position of the first occurring substring within a source string.

It takes as arguments the source string and the substring and by default starts from the beginning of the source string at zero.

It also allows a third optional argument that adds an offset to the start position.

Example of strpos()

<?php
    $sentence = "Tom, Dick, Harry, and Dick's brother work here.";

    // This prints out 5
    echo (strpos ($sentence, "Dick"));

    // This prints out 22
    echo (strpos ($sentence, "Dick", 11));
?>

The strrpos() function is similar to the strpos() function except ...

It only searches for the first character of the substring.
It searches for the last occurrence of the substring within the source string instead of the first occurrence.

Example of strrpos()

<?php
    $sentence = "Tom, Dick, Harry, and Dick's brother work here.";

    // This prints out 22
    echo (strrpos ($sentence, "Dick"));
?>

With all of these functions, false is returned if the substring isn't found within the source string.

Note: If the substring is at the start of the source string then this will return a zero value, which will give the same result as a false value if the equality operator == is used.

Therefore if testing the return value the is-identical operator === should be used.

Extracting a Found Portion of a String

The strstr() function searches for a substring within a source string and returns the first occurrence of the substring to the end of the source string.

The search is case sensitive and takes as arguments a source string and a substring.

If the substring is not found the function returns false.

The stristr() function does exactly the same except the search is not case sensitive.

Example of strstr() and stristr()

<?php
    $sentence = "Handsome is as handsome does.";

    // This prints out handsome does.
    echo (strstr ($sentence, "handsome"));

    // This prints out Handsome is as handsome does.
    echo (stristr ($sentence, "handsome"));
?>

The strrchr() function performs a similar job as the last two functions but differs in two ways.

It only searches for a single character using the first character of the supplied substring.
It searches for the last occurrence of the character within the source string, not the first.

Examples of strrchr()

<?php
    $sentence = "Handsome is as handsome does.";

    // This prints out does.
    echo (strrchr ($sentence, "done"));

    // This prints out andsome does.
    echo (strrchr ($sentence, "and"));
?>

Extracting Values from a String

This requires a knowledge of arrays, which is covered in the tutorial Arrays.

PHP provides two functions for converting strings into arrays and arrays into strings - explode() and implode()

The explode() Function

The explode() function takes a source string and returns an array of strings formed by breaking the source string at each occurrence of a delimiter string.

The function takes as arguments a delimiter string and a source string.

It also accepts an optional limit argument that determines the maximum number of elements in the returned array. When the limit is reached then the last element in the array holds whatever is left of the subject string.

Example of explode()

<?php
    $names = "Tom Dick Harry Fred George";

    // This creates an array with each name as an element.
    $names_array = explode (" ", $names);
?>

The implode() Function

The implode() function is the opposite of the explode() function. It takes an array and returns a single string formed by joining each element in the array with a glue string between each element.

The function takes as arguments a glue string and an array.

Example of implode()

<?php
    $names = array("Tom", "Dick", "Harry", "Fred", "George");

    $name_string = implode (", ", $names);

    // This prints out Tom, Dick, Harry, Fred, George.
    echo($name_string);
?>

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