Sams Teach Yourself PHP, MySQL and Apache All in One (2012)

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Put these lines into a text file named teststrtotok.php and place this file in your web server document root. When you access this script through your web browser, it should look like Figure 10.4.

Figure 10.4 Output of teststrtotok.php, a tokenized string.

The strtok() function is something of a blunt instrument, and a few tricks are required to work with it. The code first stores the delimiters to work with in a variable, $delims, on line 4. It calls strtok() on line 5, passing it the URL to tokenize and the $delims string, and stores the first result in $word. Within the conditional expression of the while loop on line 6, the code tests that $word is a string. If it isn’t, the end of the string has been reached and no further action is required.

Listing 10.3 tests the return type because a string containing two delimiters in a row would cause strtok() to return an empty string when it reaches the first of these delimiters. So, a more conventional test such as

while ($word) {
$word = strtok($delims);
}

would fail if $word is an empty string, even if the end of the source string has not yet been reached.

Having established that $word contains a string, the code can go on to work with it. If $word does not contain an empty string, print it to the browser on line 8. The code must then call strtok() again on line 10 to repopulate the $word variable for the next test. Notice that the source string tostrtok() is not passed a second time. (If were to do this, the first word of the source string would be returned once again, and you would find yourself in an infinite loop.)

Manipulating Strings with PHP

PHP provides many functions that transform a string argument, subtly or radically, as you’ll soon see.

Cleaning Up a String with trim(), ltrim(), and strip_tags()

When you acquire text from user input or an external file, you cannot always be sure that you haven’t also picked up whitespace at the beginning and end of your data. The trim() function shaves any whitespace characters, including newlines, tabs, and spaces, from both the start and end of a string. It accepts the string to modify, returning the cleaned-up version. For example:

<?php
$text = "\t\tlots of room to breathe ";
echo "<pre>$text</pre>";
// prints " lots of room to breathe ";
$text = trim($text);
echo "<pre>$text</pre>";
// prints "lots of room to breathe";
?>

Of course, this might be more work than you require. You might want to keep whitespace at the beginning of a string but remove it from the end. You can use PHP’s rtrim() function exactly as you would use trim(). However, rtrim() removes whitespace at only the end of the string argument:

<?php
$text = "\t\tlots of room to breathe ";
echo "<pre>$text</pre>";
// prints " lots of room to breathe ";
$text = rtrim($text);
echo "<pre>$text</pre>";
// prints " lots of room to breathe";
?>

PHP provides the ltrim() function to strip whitespace from only the beginning of a string. Once again, you call this function with the string you want to transform and it returns a new string, shorn of tabs, newlines, and spaces:

<?php
$text = "\t\tlots of room to breathe ";
echo "<pre>$text</pre>";
// prints " lots of room to breathe ";
$text = ltrim($text);
echo "<pre>$text</pre>";
// prints "lots of room to breathe ";
?>

It is not unusual to have to remove tags from a block of text to display it without any HTML formatting. PHP provides the strip_tags() function for this purpose. The strip_tags() function accepts two arguments: the text to transform and an optional set of HTML tags that strip_tags() can leave in place. The tags in this list should not be separated by any characters:

<?php
$string = "<p>\"I <em>simply</em> will not have it,\" <br/>said Mr Dean.</p>
<p><strong>The end.</strong></p>";
echo strip_tags($string, "<br/><p>");
?>

The previous code fragment creates an HTML-formatted string. When you call strip_tags(), you pass it the $string variable and a list of exceptions. The result is that the <br/> and <p> tags are left in place and all other tags are stripped out. In addition, the matching tag for <p>—</p>—is also removed.

The output of this snippet is as follows:

"I simply will not have it,"
said Mr Dean.

The end.

Note that the emphasis and strong formatting are gone, but the paragraphs and line breaks remain.

Replacing a Portion of a String Using substr_replace()

The substr_replace() function works similarly to the substr() function, except it enables you to replace the portion of the string that you extract. The function requires three arguments: the string to transform, the text to add to it, and the starting index; it also accepts an optional length argument. The substr_replace() function finds the portion of a string specified by the starting index and length arguments, replaces this portion with the string provided, and returns the entire transformed string.

The following code fragment for renewing a user’s membership number changes its second two characters:

<?php
$membership = "mz11xyz";
$membership = substr_replace($membership, "12", 2, 2);
echo "New membership number: $membership";
// prints "New membership number: mz12xyz"
?>

The result of this code is that the old membership number, "mz11xyz", is transformed into the new membership number, "mz12xyz".

Replacing Substrings Using str_replace

The str_replace() function is used to replace all instances of a given string within another string. It requires three arguments: the search string, the replacement string, and the master string. The function returns the transformed string.

The following example uses str_replace() to change all references to 2010 to 2012 within a master string:

<?php
$string = "<h1>The 2010 Guide to All Things Good in the World</h1>";
$string .= "<p>Site contents copyright 2010.</p>";
echo str_replace("2010","2012",$string);
?>

The str_replace() function accepts arrays as well as strings for all its arguments. This enables you to perform multiple search and replace operations on a subject string, and even on more than one subject string. Take the following snippet, for instance:

<?php
$source = array(
"The package which is at version 4.2 was released in 2005.",
"The year 2005 was an excellent time for PointyThing 4.2!");
$search = array("4.2", "2005");
$replace = array("6.3", "2012");
$source = str_replace($search, $replace, $source);
foreach($source as $str) {
echo "$str<br>";
}
?>

The output is of this snippet is as follows:

The package which is at version 6.3 was released in 2012.
The year 2012 was an excellent time for PointyThing 6.3!

When an array of strings is passed to str_replace() for its first and second arguments, it attempts to switch each search string with its corresponding replace string in the text to be transformed. When the third argument is an array, the str_replace() function returns an array of strings. The search and replace operation will have been executed on each string in the array.

Converting Case

PHP provides several functions that allow you to convert the case of a string. Changing case is often useful for string comparisons. To get an uppercase version of a string, use the strtoupper() function. This function requires only the string that you want to convert and returns the converted string:

<?php
$membership = "mz11xyz";
$membership = strtoupper($membership);
echo "$membership"; // prints "MZ11XYZ"
?>

To convert a string to lowercase characters, use the strtolower() function. Once again, this function requires the string you want to convert and returns the converted version:

<?php
$membership = "MZ11XYZ";
$membership = strtolower($membership);
echo "$membership"; // prints "mz11xyz"
?>

PHP also provides a case function that has a useful cosmetic purpose. The ucwords() function makes the first letter of every word in a string uppercase. The following fragment makes the first letter of every word in a user-submitted string uppercase:

<?php
$full_name = "violet elizabeth bott";
$full_name = ucwords($full_name);
echo $full_name; // prints "Violet Elizabeth Bott"
?>

Although this function makes the first letter of each word uppercase, it does not touch any other letters. So, if the user had had problems with her Shift key in the previous example and submitted VIolEt eLIZaBeTH bOTt, the preceding approach would not have done much to fix the string. The output would have been VIolEt ELIZaBeTH BOTt, which isn’t much of an improvement. You can deal with this by making the submitted string lowercase with the strtolower() function before invoking ucwords():

<?php
$full_name = "VIolEt eLIZaBeTH bOTt";
$full_name = ucwords(strtolower($full_name));
echo $full_name; // prints "Violet Elizabeth Bott"
?>

Finally, the ucfirst() function capitalizes only the first letter in a string. The following fragment capitalizes the first letter in a user-submitted string:

<?php
$myString = "this is my string.";
$myString = ucfirst($myString);
echo $myString; // prints "This is my string."
?>

Working with case-related string functions can prove useful when attempting to authenticate passwords that are not case sensitive, for example. If the user inputs MyPass and the stored password is mypass but you do not want the match to be case sensitive, you can attempt to match a lowercase (or uppercase) version of the user input with the lowercase (or uppercase) version of the stored password. If they match in their similarly cased format, the user can be authenticated even if he typed something different from what was actually stored.

Wrapping Text with wordwrap() and nl2br()

When you present plaintext within a web page, you are often faced with a problem in which new lines are not displayed and your text runs together into one big mess. The nl2br() function conveniently converts every new line into an HTML break. So

<?php
$string = "one line\n";
$string .= "another line\n";
$string .= "a third for luck\n";
echo nl2br($string);
?>

outputs

one line<br />
another line<br />
a third for luck<br />

The nl2br() function is great for maintaining newlines that are already in the text you are converting. Occasionally, you might want to add arbitrary line breaks to format a column of text. The wordwrap() function is perfect for this. wordwrap() requires one argument: the string to transform. By default, wordwrap() wraps lines every 75 characters and uses \n as its line break character. So, the code fragment

<?php
$string = "Given a long line, wordwrap() is useful as a means of ";
$string .= "breaking it into a column and thereby making it easier to read";
echo wordwrap($string);
?>

outputs the following:

Given a long line, wordwrap() is useful as a means of breaking it into a
column and thereby making it easier to read

Because the lines are broken with the character \n, the formatting does not show up in HTML code, of course—the output here is what you see if you view the source in your browser. The wordwrap() function has two more optional arguments: a number representing the maximum number of characters per line and a string representing the end of line string you want to use. So, applying the function call

echo wordwrap($string, 24, "<br/>\n");

to the $string variable used earlier, the output is this:

Given a long line,<br/>
wordwrap() is useful as<br/>
a means of breaking it<br/>
into a column and<br/>
thereby making it easier<br/>
to read

The wordwrap() function does not automatically break at your line limit if a word has more characters than the limit. You can, however, use an optional fourth argument to enforce this. The argument should be a positive integer. So, using wordwrap() in conjunction with the fourth argument, you can wrap a string even when it contains words that extend beyond the limit you are setting. This fragment

<?php
$string = "As usual you will find me at http://www.witteringonaboutit.com/";
$string .= "chat/eating_green_cheese/forum.php. Hope to see you there!";
echo wordwrap($string, 24, "<br/>\n", 1);
?>

outputs

As usual you will find<br/>
me at<br/>
http://www.witteringonab<br/>
outit.com/chat/eating_gr<br/>
een_cheese/forum.php.<br/>
Hope to see you there!

instead of

As usual you will find<br/>
me at<br/>
http://www.witteringonaboutit.com/chat/eating_green_cheese/forum.php. <br/>
Hope to see you there!

Breaking Strings into Arrays with explode()

The delightfully named explode() function is similar in some ways to strtok(). But explode() breaks up a string into an array, which you can then store, sort, or examine as you want. The explode() function requires two arguments: the delimiter string that you want to use to break up the source string and the source string itself. The function optionally accepts a third argument that determines the maximum number of pieces the string can be broken into. The delimiter string can include more than one character, all of which form a single delimiter (unlike multiple delimiter characters passed to strtok(), each of which will be a delimiter in its own right). The following fragment breaks up a date and stores the result in an array:

<?php
$start_date = "2012-02-19";
$date_array = explode("-", $start_date);
// $date_array[0] == "2012"
// $date_array[1] == "02"
// $date_array[2] == "19"
echo $date_array[0]."-".$date_array[1]."-".$date_array[2];
//prints 2012-02-19
?>

Now that your head is full with some common PHP string functions, let’s move on to date and time functions.

Using Date and Time Functions in PHP

The following sections introduce you to the date- and time-related functions specifically in PHP. Try out each listing for yourself to see how simple and powerful these functions can be.

Getting the Date with time()

PHP’s time() function gives you all the information you need about the current date and time. It requires no arguments and returns an integer. For us humans, the returned number is a little hard on the eyes, but it’s extremely useful nonetheless:

echo time();
// sample output: 1326853185
// this represents January 17, 2012 at 09:19PM

The integer returned by time() represents the number of seconds elapsed since midnight GMT on January 1, 1970. This moment is known as the UNIX epoch, and the number of seconds that have elapsed since then is referred to as a timestamp. PHP offers excellent tools to convert a timestamp into a form that humans are comfortable with. Even so, you might think, “Isn’t a timestamp a needlessly convoluted way of storing a date?” In fact, the opposite is true. From just one number, you can extract enormous amounts of information. Even better, a timestamp can make date arithmetic much easier than you might imagine.

Think of a homegrown date system in which you record days of the month as well as months and years. Now imagine a script that must add one day to a given date. If this date happened to be 31 December 1999, rather than adding 1 to the date, you’d have to write code to set the day of the month to 1, the month to January, and the year to 2000. Using a timestamp, you need add only a day’s worth of seconds (60 * 60 * 24, or 86,400) to your current figure and you’re done. You can convert this new figure into something friendlier, at your leisure.

Converting a Timestamp with getdate()

Now that you have a timestamp to work with, you must convert it before you present it to the user. getdate() optionally accepts a timestamp and returns an associative array containing information about the date. If you omit the timestamp, getdate() works with the current timestamp as returned by time(). Table 10.3 lists the elements contained in the array returned by getdate().

Table 10.3 The Associative Array Returned by getdate()

Listing 10.4 uses getdate() in line 2 to extract information from a timestamp, employing a foreach statement to print each element (line 3). You can see typical output of this script, called getdate.php, in Figure 10.5.

Figure 10.5 Using getdate().

Listing 10.4 Acquiring Date Information with getdate()