PHP 7

This chapter demonstrates various ways to manipulate text strings in PHP scripts.

PHP provides a number of built-in functions to perform a comparison of two text strings. The simple strcmp() function accepts two string arguments for comparison and will return one of three integer values depending on the result. When the strings exactly match, strcmp() will return zero. When the first string argument is greater than the second, strcmp() will return 1, but when the first string argument is less than the second, strcmp() will return -1.

Strictly speaking, the strcmp() returned values will be a positive integer, zero, or a negative integer – but are typically values of 1, 0, or -1.

The strncmp() function works in a similar way, but accepts a third integer argument to specify the number of characters from the start of the strings to be compared.

The strcmp() and strncmp() functions attach different importance to uppercase and lowercase characters when comparing strings. When you prefer to ignore case, you can use the alternative companion functions strcasecmp() and strncasecmp() instead.

To appreciate the results from each of the four comparison functions it is useful to understand how the comparisons are actually made. Each character has a standard numerical “ASCII” value where lowercase a-z is in the range 97-122 and uppercase A-Z is in the range 65-90. Comparing the first value in each range we see that “a” (97) is greater than “A” (65). Supplying these as arguments the strcmp() function would therefore return 1, as the first argument is greater than the second. Conversely, if you specify “A” (65) as the first argument and “a” (97) as the second argument then the strcmp() function would return -1, as the first argument is less than the second. With string comparisons, each character is compared in sequence to ensure that strings containing the same characters in different order are not seen to be incorrectly equal. For example, comparing “ABC” and “BAC” the first character “A” (65) is less than first character “B” (66) so the strcmp() function would return -1, as the first argument is less than the second.

ASCII is an abbreviation for the American Standard Code for Information Exchange that specifies the universal standard character coding scheme.

The ASCII value of any character can be found by specifying the character as an argument to the PHP ord() function, and the length of a string can be found by specifying it as the argument to the PHP strlen() function.

Begin a PHP script with statements to initialize four variables with string values

Next, add statements to compare the strings

echo “’$str1’ versus ‘$str2’ : “ .strcmp( $str1 , $str2 ). ’<br>’ ;

echo “’$str1’ versus ‘$str3’ : “ .strcmp( $str1 , $str3 ). ’<br>’ ;

echo “’$str1’ versus ‘$str4’ : “ .strcmp( $str1 , $str4 ). ’<hr>’ ;

Now, add a statement for a case-insensitive comparison

Finally, add a loop to count and display the total ASCII code value of the first string

Save the document in your web server’s /htdocs directory as characters.php then open the page via HTTP to see the string comparisons

Character order is relevant as the ASCII totals for two differently ordered strings could be equal, but the strings would not match.

PHP provides a number of built-in functions to search a string to find a specified substring or single character. The simple strpos() function accepts two arguments to specify the string in which to search, and the substring to find. It will search in sequence from the start of the string to find a match. When a match is found the search halts and the strpos() function returns an integer, which is the character index number position within the string at which the first occurrence of a match begins. When no match is found the strpos() function returns FALSE .

The strrpos() function works in a similar way but returns the index number position at which the first occurrence of a match begins when searching in reverse order, from the end of the string.

Other PHP search functions can return a part of the searched string, rather than an index number indicating a match position.

The strstr() function accepts two arguments to specify the string in which to search, and the substring to find. It will search in sequence from the start of the string to find a match. When a match is found, the search halts and the strstr() function returns the remainder of the searched string from where the first occurrence of a match begins. When no match is found the strstr() function returns NULL .

Notice that there is no strrstr() (companion function to strstr() ) to search in reverse order.

Similarly, where character case is unimportant, you can use the companion stristr() function to make a case-insensitive search. This will return the remainder of the searched string from where the first occurrence of a case-insensitive match begins.

The strchr() function works in a similar way but accepts two arguments to specify the string in which to search, and a single character to find. As you might expect, the companion strrchr() function begins searching in reverse order, from the end of the string. Both return the remainder of the searched string from where the first occurrence of a match begins.

Begin a PHP script with statements to initialize a variable with a string value and report its length

Next, add statements to search the string, both forwards and reverse, and report the position of a given substring

Now, add statements to search the string, both case- sensitive and case-insensitive, and return the remainder of the string following a substring match

echo “<hr>Substring from first ‘us’ : “ .strstr( $str , ‘us’ ) ;

Finally, add statements to search the string, both forwards and reverse, and return the remainder of the string following a character match

echo “<br>Characters from final ‘u’ : “ .strrchr( $str , ‘u’ ) ;

Save the document in your web server’s /htdocs directory as search.php then open the page via HTTP to see the search results

There are three occurrences of ‘us’ in this string, but only the first and third are matched.

A substring can be extracted from a string by stating the string, and index position of a substring within the string, as arguments to the substr() function. Optionally, a third argument can specify the substring length. You may replace a substring using the substr_ replace() function to specify string, substring, index position and length arguments. The total number of occurrences of a substring within a string can be found using the substr_count() function:

Begin a PHP script with statements to initialize a variable with a string value and count substrings

echo “’ $str ’<br>’SQL’ Count: “ .substr_count( $str , ‘SQL’ ) ;

Next, add statements to extract two substrings

Now, add a statement to initialize a variable with a string

Finally, add statements to replace a substring with a new string value and to display the modified string

Save the document in your web browser’s /htdocs directory as substring.php then open the page via HTTP to see the extracted substrings and modified string

The length argument in substr_replace() specifies the length of the substring to be replaced. In this example, it is 3 – to replace the three characters ‘SQL’ with a longer string.

PHP provides functions to easily modify the character case of a specified string argument. The strtolower() function changes all characters to lowercase and strtoupper() changes them all to uppercase. Additionally, the ucfirst() function makes only the first string character uppercase, whereas the ucword() function makes the first character of every word in the string into uppercase:

Begin a PHP script with statements to initialize a variable with a string and display its value

Next, add statements to display a lowercase version

Now, add statements to display an uppercase version

Finally, add statements to display a capitalized string version and a capitalized words version

Save the document in your web server’s /htdocs directory as case.php then open the page via HTTP to see the changed case versions of the original string

The ucfirst() function only changes the first character of a string. Other uppercase characters will remain unless first changed to lowercase with the strtolower() function, as seen here.

PHP provides a number of built-in functions to conveniently format strings by manipulating their characters. The simple strrev() function accepts a single string argument and returns that string in reversed character order, so it reads back to front.

The strrpt() function accepts two arguments to specify a string, and an integer of how many total times that string should be repeated in the string it will return.

The strpad() function accepts three arguments to specify a string, a total length of the character string it will return, and a character or substring pattern with which to fill the difference between the original string and the specified returned string length. The padding will, by default, be added to the end of the original string but can be added to its start by adding a fourth argument using a special STR_PAD_LEFT flag.

The trim() function can accept a single string argument and will return a string in which all white-space characters (spaces, line returns, tabs) have been removed from the start and end of the original string. Optionally, a second argument can specify a character or pattern to be removed from the start and end of the original string, in place of the white-space default.

Similarly, where you only want to remove characters from the start of the original string, you can use the companion ltrim() function, or where you only want to remove characters from the end of the original string, you can use the companion rtrim() function.

The PHP implode() and explode() functions can be used to convert arrays to strings, and strings to arrays – see here for more details.

A string can be split into individual parts using the strtok() function to specify the string and a delimiter token around which the parts should be split. For example, if you want to split a string into individual words you can specify the space character as the delimiter token. The first part of the string, up to the delimiter token will be returned by the function. Interestingly, the strtok() function remembers its position in the string, so subsequent calls need only specify the delimiter token to return the next part of the string, until no further delimiters are found. Splitting a string in this way can best be achieved using a loop to make subsequent calls to the strtok() function, until it reaches the end of the string.

Begin a PHP script with statements to initialize a variable with a string and display its value

Next, add statements to display reversed, repeated and trimmed versions of the original string

Now, add a statements to display a 30-character version of the string, padded with asterisks at the beginning

Finally, add statements to split the string around spaces and display each individual part separated by an ... ellipsis

Save the document in your web server’s /htdocs directory as format.php then open the page via HTTP to see the string formatted in several ways

You must specify the delimiter on each subsequent call to strtok() to have it continue forward to the next part of the string.

The PHP date() function will return a date string when called, but requires a string argument to specify a format for the date string. This format string can comprise a series of letter options for date and time. For example, date( ‘n/j/y’ ) might return “4/22/16”. Popular options are listed below along with a brief description:

You can discover more date() function options in the PHP manual online at php.net/manual

By default, the timezone is set to the Universal Time Clock (UTC) but you can set it to your own timezone by specifying it as an argument to the date_default_timezone_set() function, and see the currently set timezone with date_default_timezone_get() .

You may also create your own timestamp using the intelligent strtotime() function. This can accept a date string argument and return a timestamp that can be supplied as an optional second argument to the date() function. The argument specified to strtotime() can be a regular text date, such as “July 4, 2017”. Additionally, you can specify an argument such as “yesterday”, “+3months” or “next Wednesday” and the strtotime() function will try to figure it out and return an appropriate timestamp.

Begin a PHP script with statements to display the current date, day, time and current default timezone

Next, add statements to change the default timezone and display a confirmation, then show the current time there

Now, add statements to create a timestamp for the next day, then display its day name and date

Finally, add statements to create a timestamp for a memorable date, then display its month and day number

Save the document in your web server’s /htdocs directory as date.php then open the page via HTTP to see the date strings formatted by the options

Notice that you can include separator characters such as : and / in the format string.

Some countries prefer date order of M/D/ Y while others prefer D/M/ Y so you can choose your preferred date format options.

There are two PHP functions available to encode HTML code, so that all characters of special significance or unusual characters are replaced by “entity” equivalents. The htmlentities() function encodes all characters below, which each have an entity equivalent:

Call the PHP function get_html_translation_ table() with the constant argument of HTML_ENTITIES or HTML_SPECIALCHARS to return an array of all represented characters.

Unless you are concerned about non-English language characters, it is generally preferable to use the alternative htmlspecialchars() function to encode only characters of special HTML significance:

One good reason to encode HTML snippets with PHP is to prevent malicious JavaScript code being executed unintentionally by the web browser. Encoding HTML tags into entities ensures that the HTML <script> tag will not be recognized, so its JavaScript code contents will not be executed:

Create a PHP script with statements to initialize a variable with an HTML snippet and display its value

Save the document in your web server’s /htdocs directory as encode.php then open the page via HTTP to hopefully see the HTML code snippet

The browser has interpreted the code and relocated to the server’s index page because it recognized the HTML <script> tag.

Return to the PHP script and insert a statement to encode special HTML characters

Save the edited document and reopen the page via HTTP again to see the HTML code snippet

Use the View Source facility in your web browser to see the special character entity equivalents encoded by PHP

The PHP function html_entity_decode() can be used to unencode all entities back to their original character state.

• The PHP built-in string comparison functions strcmp() , strncmp() , strcasecmp() and strncasecmp() each typically return a result of 1 (greater), 0 (equal) or -1 (less)

• String comparisons are based on the numerical ASCII value of each character, compared in sequence to account for order

• The numerical index position of a substring within a searched string can be found using strpos() and strrpos() functions

• The search functions strstr() , stristr() , strchr() and strrchr() each return the remainder of a searched string on success

• The substring functions substr() , substr_replace() and substr_count() can extract, replace or count occurrences

• The characters in a string can be reversed using strrev() , or the string can be repeated using strrpt()

• Padding characters can be added to a string using strpad() and characters can be removed using trim() , ltrim() or rtrim()

• A string can be split into individual parts by specifying a delimiter to the strtok() function

• The date() function requires a string argument that specifies options to determine the format of its returned date string

• The date_default_timezone_set() function can be used to specify an alternative to the UTC default timezone

• The strtotime() function will attempt to return an appropriate timestamp for whatever date or time argument it receives

• The htmlentities() function will encode all string characters for which there is an equivalent entity

• The htmlspecialchars() function will encode only characters of special HTML significance to avoid recognition by a browser

Option:	Description:	Example:
Y	Year as four digits	2014
y	Year as two digits	14
n	Month as one or two digits	7
m	Month as two digits	07
F	Month full name	February
M	Month name as three letters	Feb
j	Day as one or two digits	4
d	Day as two digits	04
l	Weekday full name	Monday
D	Weekday as three letters	Mon
S	Ordinal suffix as two letters	th
H	Hour in 24-hour format	14
i	Minutes	45
s	Seconds	30
a	Ante or post meridiem	am