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2.1 TextWhen they're used in computer programs, pieces of text are called strings. This is because they consist of individual characters, strung together. Strings can contain letters, numbers, punctuation, spaces, tabs, or any other characters. Some examples of strings are I would like 1 bowl of soup, and "Is it too hot?" he asked, and There's no spoon!. A string can even contain the contents of a binary file such as an image or a sound. The only limit to the length of a string in a PHP program is the amount of memory your computer has. 2.1.1 Defining Text StringsThere are a few ways to indicate a string in a PHP program. The simplest is to surround the string with single quotes: print 'I would like a bowl of soup.'; print 'chicken'; print '06520'; print '"I am eating dinner," he growled.'; Since the string consists of everything inside the single quotes, that's what is printed: I would like a bowl of soup.chicken06520"I am eating dinner," he growled. The output of those four print statements appears all on one line. No linebreaks are added by print.[1]
The single quotes aren't part of the string. They are delimiters, which tell the PHP interpreter where the start and end of the string is. If you want to include a single quote inside a string surrounded with single quotes, put a backslash (\) before the single quote inside the string: print 'We\'ll each have a bowl of soup.'; The \' sequence is turned into ' inside the string, so what is printed is: We'll each have a bowl of soup. The backslash tells the PHP interpreter to treat the following character as a literal single quote instead of the single quote that means "end of string." This is called escaping, and the backslash is called the escape character. An escape character tells the system to do something special with the character that comes after it. Inside a single-quoted string, a single quote usually means "end of string." Preceding the single quote with a backslash changes its meaning to a literal single quote character.
The escape character can itself be escaped. To include a literal backslash character in a string, put a back slash before it: print 'Use a \\ to escape in a string'; This prints: Use a \ to escape in a string The first backslash is the escape character: it tells the PHP interpreter that something different is going on with the next character. This affects the second backslash: instead of the special action ("treat the next character literally"), a literal backslash is included in the string. Note that these are backslashes that go from top left to bottom right, not forward slashes that go from bottom left to top right. Remember that two forward slashes ( //) indicate a comment. You can include whitespace such as newlines in single-quoted strings: print '<ul> <li>Beef Chow-Fun</li> <li>Sauteed Pea Shoots</li> <li>Soy Sauce Noodles</li> </ul>'; This puts the HTML on multiple lines: <ul> <li>Beef Chow-Fun</li> <li>Sauteed Pea Shoots</li> <li>Soy Sauce Noodles</li> </ul> Since the single quote that marks the end of the string is immediately after the </ul>, there is no newline at the end of the string. The only characters that get special treatment inside single-quoted strings are backslash and single quote. Everything else is treated literally. You can also delimit strings with double quotes. Double-quoted strings are similar to single-quoted strings, but they have more special characters. These special characters are listed in Table 2-1.
The biggest difference between single-quoted and double-quoted strings is that when you include variable names inside a double-quoted string, the value of the variable is substituted into the string, which doesn't happen with single-quoted strings. For example, if the variable $user held the value Bill, then 'Hi $user' is just that: Hi $user. However, "Hi $user" is Hi Bill. I get into this in more detail later in this chapter in Section 2.3. As mentioned in Section 1.3, you can also define strings with the here document syntax. A here document begins with <<< and a delimiter word. It ends with the same word at the beginning of a line. Example 2-1 shows a here document. Example 2-1. Here document<<<HTMLBLOCK <html> <head><title>Menu</title></head> <body bgcolor="#fffed9"> <h1>Dinner</h1> <ul> <li> Beef Chow-Fun <li> Sauteed Pea Shoots <li> Soy Sauce Noodles </ul> </body> </html> HTMLBLOCK In Example 2-1, the delimiter word is HTMLBLOCK. Here document delimiters can contain letters, numbers, and the underscore character. The first character of the delimiter must be a letter or the underscore. It's a good idea to make all the letters in your here document delimiters uppercase to visually set off the here document. The delimiter that ends the here document must be alone on its line. The delimiter can't be indented and no whitespace, comments, or other characters are allowed after it. The only exception to this is that a semicolon is allowed immediately after the delimiter to end a statement. In that case, nothing can be on the same line after the semicolon. The code in Example 2-2 follows these rules to print a here document. Example 2-2. Printing a here documentprint <<<HTMLBLOCK <html> <head><title>Menu</title></head> <body bgcolor="#fffed9"> <h1>Dinner</h1> <ul> <li> Beef Chow-Fun <li> Sauteed Pea Shoots <li> Soy Sauce Noodles </ul> </body> </html> HTMLBLOCK; Here documents obey the same escape-character and variable substitution rules as double-quoted strings. These make them especially useful when you want to define or print a string that contains a lot of text or HTML with some variables mixed in. Later on in the chapter, Example 2-22 demonstrates this. To combine two strings, use a . (period), the string concatenation operator. Here are some combined strings: print 'bread' . 'fruit'; print "It's a beautiful day " . 'in the neighborhood.'; print "The price is: " . '$3.95'; print 'Inky' . 'Pinky' . 'Blinky' . 'Clyde'; The combined strings print as: breadfruit It's a beautiful day in the neighborhood. The price is: $3.95 InkyPinkyBlinkyClyde 2.1.2 Manipulating TextPHP has a number of built-in functions that are useful when working with strings. This section introduces the functions that are most helpful for two common tasks: validation and formatting. The "Strings" chapter of the PHP online manual, at http://www.php.net/strings, has information on other built-in string handling functions. 2.1.2.1 Validating stringsValidation is the process of checking that input coming from an external source conforms to an expected format or meaning. It's making sure that a user really entered a ZIP Code in the "ZIP Code" box of a form or a reasonable email address in the appropriate place. Chapter 6 delves into all the aspects of form handling, but since submitted form data is provided to your PHP programs as strings, this section discusses how to validate those strings. The trim( ) function removes whitespace from the beginning and end of a string. Combined with strlen( ), which tells you the length of a string, you can find out the length of a submitted value while ignoring any leading or trailing spaces. Example 2-3 shows you how. (Chapter 3 discusses in more detail the if( ) statement used in Example 2-3.) Example 2-3. Checking the length of a trimmed string// $_POST['zipcode'] holds the value of the submitted form parameter
// "zipcode"
$zipcode = trim($_POST['zipcode']);
// Now $zipcode holds that value, with any leading or trailing spaces
// removed
$zip_length = strlen($zipcode);
// Complain if the ZIP code is not 5 characters long
if ($zip_length != 5) {
print "Please enter a ZIP code that is 5 characters long.";
}Using trim( ) protects against someone who types a ZIP Code of 732 followed by two spaces. Sometimes the extra spaces are accidental and sometimes they are malicious. Whatever the reason, throw them away when appropriate to make sure that you're getting the string length you care about. You can chain together the calls to trim( ) and strlen( ) for more concise code. Example 2-4 does the same thing as Example 2-3. Example 2-4. Concisely checking the length of a trimmed stringif (strlen(trim($_POST['zipcode'])) != 5) {
print "Please enter a ZIP code that is 5 characters long.";
}Four things happen in the first line of Example 2-4. First, the value of the variable $_POST['zipcode'] is passed to the trim( ) function. Second, the return value of that function — $_POST['zipcode'] with leading and trailing whitespace removed — is handed off to the strlen( ) function, which then returns the length of the trimmed string. Third, this length is compared with 5. Last, if the length is not equal to 5, then the print statement inside the if( ) block runs. To compare two strings, use the equality operator (= =), as shown in Example 2-5. Example 2-5. Comparing strings with the equality operatorif ($_POST['email'] == 'president@whitehouse.gov') {
print "Welcome, Mr. President.";
}The print statement in Example 2-5 runs only if the submitted form parameter email is the all-lowercase president@whitehouse.gov. When you compare strings with = =, case is important. president@whitehouse.GOV is not the same as President@Whitehouse.Gov or president@whitehouse.gov. To compare strings without paying attention to case, use strcasecmp( ). It compares two strings while ignoring differences in capitalization. If the two strings you provide to strcasecmp( ) are the same (independent of any differences between upper- and lowercase letters), it returns 0. Example 2-6 shows how to use strcasecmp( ). Example 2-6. Comparing strings case-insensitivelyif (strcasecmp($_POST['email'], 'president@whitehouse.gov') == 0) {
print "Welcome back, Mr. President.";
}The print statement in Example 2-6 runs if the submitted form parameter email is President@Whitehouse.Gov, PRESIDENT@WHITEHOUSE.GOV, presIDENT@whiteHOUSE.GoV, or any other capitalization of president@whitehouse.gov. 2.1.2.2 Formatting textThe printf( ) function gives you more control (compared to print) over how the output looks. You pass printf( ) a format string and a bunch of items to print. Each rule in the format string is replaced by one item. Example 2-7 shows printf( ) in action. Example 2-7. Formatting a price with printf( )$price = 5; $tax = 0.075;
printf('The dish costs $%.2f', $price * (1 + $tax));This prints: The dish costs $5.38 In Example 2-7, the format rule %.2f is replaced with the value of $price * (1 + $tax) and formatted so that it has two decimal places. Format string rules begin with % and then have some optional modifiers that affect what the rule does:
After the modifiers come a mandatory character that indicates what kind of value should be printed. The three discussed here are d for decimal number, s for string, and f for floating-point number. If this stew of percent signs and modifiers has you scratching your head, don't worry. The most frequent use of printf( ) is probably to format prices with the %.2f format rule as shown in Example 2-7. If you absorb nothing else about printf( ) for now, just remember that it's your go-to function when you want to format a decimal value. But if you delve a little deeper, you can do some other handy things with it. For example, using the 0 padding character and a minimum width, you can format a date or ZIP Code properly with leading zeroes, as shown in Example 2-8. Example 2-8. Zero-padding with printf( )$zip = '6520';
$month = 2;
$day = 6;
$year = 2007;
printf("ZIP is %05d and the date is %02d/%02d/%d", $zip, $month, $day, $year);Example 2-8 prints: ZIP is 06520 and the date is 02/06/2007 The sign modifier is helpful for explicitly indicating positive and negative values. Example 2-9 uses it to display a some temperatures. Example 2-9. Displaying signs with printf( )$min = -40;
$max = 40;
printf("The computer can operate between %+d and %+d degrees Celsius.", $min, $max);Example 2-9 prints: The computer can operate between -40 and +40 degrees Celsius. To learn about other printf( ) format rules, visit http://www.php.net/sprintf. Another kind of text formatting is to manipulate the case of strings. The strtolower( ) and strtoupper( ) functions make all-lowercase and all-uppercase versions, respectively, of a string. Example 2-10 shows strtolower( ) and strtoupper( ) at work. Example 2-10. Changing caseprint strtolower('Beef, CHICKEN, Pork, duCK');
print strtoupper('Beef, CHICKEN, Pork, duCK');Example 2-10 prints: beef, chicken, pork, duck BEEF, CHICKEN, PORK, DUCK The ucwords( ) function uppercases the first letter of each word in a string. This is useful when combined with strtolower( ) to produce nicely capitalized names when they are provided to you in all uppercase. Example 2-11 shows how to combine strtolower( ) and ucwords( ). Example 2-11. Prettifying names with ucwords( )print ucwords(strtolower('JOHN FRANKENHEIMER'));Example 2-11 prints: John Frankenheimer With the substr( ) function, you can extract just part of a string. For example, you may only want to display the beginnings of messages on a summary page. Example 2-12 shows how to use substr( ) to truncate the submitted form parameter comments. Example 2-12. Truncating a string with substr( )// Grab the first thirty characters of $_POST['comments'] print substr($_POST['comments'], 0, 30); // Add an ellipsis print '...'; If the submitted form parameter comments is: The Fresh Fish with Rice Noodle was delicious, but I didn't like the Beef Tripe. Example 2-12 prints: The Fresh Fish with Rice Noodl... The three arguments to substr( ) are the string to work with, the starting position of the substring to extract, and the number of characters to extract. The beginning of the string is position 0, not 1, so substr($_POST['comments'], 0, 30) means "extract 30 characters from $_POST['comments'] starting at the beginning of the string." When you give substr( ) a negative number for a start position, it counts back from the end of the string to figure out where to start. A start position of -4 means "start four characters from the end." Example 2-13 uses a negative start position to display just the last four digits of a credit card number. Example 2-13. Extracting the end of a string with substr( )print 'Card: XX'; print substr($_POST['card'],-4,4); If the submitted form parameter card is 4000-1234-5678-9101, Example 2-13 prints: Card: XX9101 As a shortcut, use substr($_POST['card'],-4) instead of substr($_POST['card'], -4,4). When you leave out the last argument, substr( ) returns everything from the starting position (whether positive or negative) to the end of the string. Instead of extracting a substring, the str_replace( ) function changes parts of a string. It looks for a substring and replaces the substring with a new string. This is useful for simple template-based customization of HTML. Example 2-14 uses str_replace( ) to set the class attribute of <span> tags. Example 2-14. Using str_replace( )print str_replace('{class}',$my_class,
'<span class="{class}">Fried Bean Curd<span>
<span class="{class}">Oil-Soaked Fish</span>');If $my_class is lunch, then Example 2-14 prints: <span class="lunch">Fried Bean Curd<span> <span class="lunch">Oil-Soaked Fish</span> Each instance of {class} (the first argument to str_replace( )) is replaced by lunch (the value of $my_class) in the string that is the third argument passed to str_replace( ). |
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< Day Day Up > |
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, 
,
, and 
. The PHP interpreter only
understands straight quotes as string delimiters. If
you're writing PHP programs in a word processor or
text editor that puts curly quotes in your programs, you have two
choices: tell your word processor to stop it or use a different one.
A program such as emacs, vi, BBEdit, or Windows Notepad leaves your
quotes alone.