Tài liệu Zend PHP Certification Study Guide- P6 ppt

84 Chapter 4 Arrays <?php $a = array (‘a’ => 10, 20, 30, 40); $b = array (‘a’ => 20, 20, 30, 40); $array = array_merge_recursive ($a, $b); var_dump ($array); ?> This results in the following array: array(7) { [“a”]=> array(2) { [0]=> int(10) [1]=> int(20) } [0]=> int(20) [1]=> int(30) [2]=> int(40) [3]=> int(20) [4]=> int(30) [5]=> int(40) } In this case, $a[‘a’] and $b[‘a’] are combined together into the $array[‘a’] array. Intersection and Difference If you want to extract all the elements that are common to two or more arrays, you can use the array_intersect(): <?php $a = array (‘a’ => 20, 36, 40); $b = array (‘b’ => 20, 30, 40); 05 7090 ch04 7/16/04 8:43 AM Page 84 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. 85 Serializing Arrays $array = array_intersect ($a, $b); var_dump ($array); ?> Here’s the output: array(2) { [“a”]=> int(20) [1]=> int(40) } As you can see, this function only checks whether the values are the same—the keys are ignored (although the key of the leftmost array is preserved). If you want to include them in the check, you should use array_intersect_assoc() instead: <?php $a = array (‘a’ => 20, 36, 40); $b = array (‘b’ => 20, 30, 40); $array = array_intersect_assoc ($a, $b); var_dump ($array); ?> In this case, the result will be a one-element array because the two 20 values in $a and $b have different keys: array(1) { [1]=> int(40) } If you want to calculate the difference between two or more arrays—that is, elements that only appear in one of the arrays but not in any of the others—you will need to use either array_diff() or array_diff_assoc() instead. Serializing Arrays Given their flexibility, arrays are often used to store all sorts of information, and it is handy to be able to save their contents at the end of a script and retrieve them later on. This is done through a process, known as “serialization,” in which the contents of an array are rendered in a format that can later be used to rebuild the array in memory. 05 7090 ch04 7/16/04 8:43 AM Page 85 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. 86 Chapter 4 Arrays In PHP, serialization is taken care of by two functions: n serialize() renders the array in a format that can be safely saved to any contain- er (such as a database field or a file) capable of handling textual content. n unserialize() takes a serialized input and rebuilds the array in memory. Using these two functions is very easy: <?php $a = array (‘a’ => 20, 36, 40); $saved = serialize ($a); // Your script may stop here if you save the contents // of $saved in a file or database field $restored = unserialize ($saved); ?> The serialization functionality is very flexible and will be able to save everything that is stored in your array—except, of course, for resource variables, which will have to be re- created when the array is unserialized. Exam Prep Questions 1. Which of the following types can be used as an array key? (Select three.) A. Integer B. Floating-point C. Array D. Object E. Boolean Answers A, B, and E are correct.A Boolean value will be converted to either 0 if it is false or 1 if it is true, whereas a floating-point value will be truncated to its integer equivalent. Arrays and objects, however, cannot be used under any circum- stance. 05 7090 ch04 7/16/04 8:43 AM Page 86 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. 87 Exam Prep Questions 2. Which of the following functions can be used to sort an array by its keys in descending order? A. sort B. rsort C. ksort D. krsort E. reverse_sort D is correct.The sort() and rsort() functions operate on values, whereas ksort() sorts in ascending order and reverse_sort() is not a PHP function. 3. What will the following script output? <?php $a = array (‘a’ => 20, 1 => 36, 40); array_rand ($a); echo $a[0]; ?> A. A random value from $a B. ‘a’ C. 20 D. 36 E. Nothing Only E is correct.The $a array doesn’t have any element with a numeric key of zero, and the array_rand() function does not change the keys of the array’s ele- ments—only their order. Questions of this type are in the exam not to trick you, but rather as a way to test your ability to troubleshoot a problem. In this particular example, a developer who is well versed in PHP recognizes the problem immediately, whereas a less experienced program- mer will be sidetracked by thinking that something is wrong with the function being called. After all, these kinds of bugs, usually caused by distraction or typos, are quite com- mon in real-life code. 05 7090 ch04 7/16/04 8:43 AM Page 87 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. 05 7090 ch04 7/16/04 8:43 AM Page 88 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. 5 Strings and Regular Expressions Terms You’ll Need to Understand n The == and === operators n Regular expression n PCRE Techniques You’ll Need to Master n Formatting strings n Comparing strings n Modifying string contents n Using regular expressions for pattern matching and extraction. n Joining and splitting strings The Web is largely a text-oriented environment. Data is submitted to websites in the form of text strings, and the response (be it in HTML, XML, or even an image format) is generally text as well. Accordingly, being able to analyze and manipulate text is a core skill of any PHP programmer. Comparing Strings In this section, you will learn how to test whether two strings are equal, or whether one string exists inside of another string. 06 7090 ch05 7/16/04 8:42 AM Page 89 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. 90 Chapter 5 Strings and Regular Expressions Comparison with == and === The most basic way of comparing any two entities in PHP is using the == operator (called the is equal operator).When the == operator tests the equivalence of two entities, it first reduces them to a common type.This often causes unexpected results. For exam- ple, the following code outputs $a and $b are equal: $a = ‘Hello World’; $b = 0; if($a == $b) { print “\$a and \$b are equal\n”; } else { print “\$a and \$b are not equal\n”; } The reason this happens is that $a is a string type and $b is an integer, so the Zend Engine needs to convert them to a common type for comparison. == is a weak operator, so it converts to the more lenient type, namely integer.The integer representation of ‘Hello World’ is 0, so $a == $b is true. == should only be used to compare strings if you are certain that both its operands are in fact strings. PHP also provides the stronger equivalence operator === (called the is identical opera- tor).Whereas the == was too weak to be useful in many situations, === is often too strong. === performs no type-homogenization, and requires that both operands be of the same type before a comparison can be successful.Thus, the following code outputs $a and $b are not equal: $a = 1; $b = “1”; if($a === $b) { print “\$a and \$b are equal\n”; } else { print “\$a and \$b are not equal\n”; } This result occurs because $a is internally held as an integer, whereas $b, by virtue of its being quoted, is a string. Thus, === can be dangerous to use if you are not certain that both operands are strings. Tip You can force a variable to be cast to strings by the use of casts. Thus, if( (string) $a === (string) $b) { } will convert both $a and $b to strings before performing the conversion. This produces the results you expect, but is a bit clumsy—using the strcmp family of functions is generally preferred. 06 7090 ch05 7/16/04 8:42 AM Page 90 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. 91 Comparing Strings Using strcmp and Friends The preferred way of comparing two entities as strings is to use the strcmp() function. strcmp() takes two arguments and compares them lexigraphically (also known as diction- ary ordering, as it is the same logic used in sorting words in a dictionary). strcmp() returns 0 if the two strings are identical.Thus this code, which gave us trouble before, will correctly output that $a and $b are the same: $a = 1; $b = “1”; if(strcmp($a, $b) == 0) { print “\$a and \$b are the same\n”; } else { print “\$a and \$b are different\n”; } If its two operands are not the same, strcmp() will return -1 if the first operand would appear before the second in a dictionary, and 1 if the first operand would appear after the second in a dictionary.This behavior makes it very useful for sorting arrays of words. In fact, the following two bits of code will sort the array $colors in the same fashion (in dictionary order): $colors = array(“red”, “blue”, “green”); sort($colors, SORT_STRING); and $colors = array(“red”, “blue”, “green”); usort($colors, ‘strcmp’); By itself, this is not very useful. (sort() should be preferred over usort() when per- forming equivalent tasks), but strcmp() has some sibling functions that perform similar tasks. strcasecmp() is identical to strcmp() except that it performs comparisons that are not case sensitive.This means that the following code that will output $a is the same as HELLO, modulo case: $a = ‘hello’; if(strcasecmp($a, ‘HELLO’)) { print “\$a is the same as HELLO, modulo case\n”; } Also, RED will come after blue when sorted via strcasecmp(), whereas with strcmp(), RED will come before blue. 06 7090 ch05 7/16/04 8:42 AM Page 91 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. 92 Chapter 5 Strings and Regular Expressions Matching Portions of Strings You’ve seen how to match strings exactly, but sometimes you only need to match a por- tion of a string.When only a portion of a string is considered, it is referred to as a sub- string. Specifically, a substring is any portion of a string. For example, PHP is a substring of the string PHP is a scripting language. Matching Leading Substrings To match only the leading portion of strings, PHP provides the strncmp() family of functions. strncmp() and strncasecmp() are identical to strcmp() and strcasecmp(), but both take a third parameter, $n, that instructs PHP to compare only the first $n char- acters of both strings.Thus strncmp(‘figure1.gif’, ‘figure2.gif’, 6) will return 0 (equal) because only the first six characters of each string is compared. Matching Substrings at Arbitrary Offsets If you need to determined simply whether a substring exists anywhere inside a given string, you should use strstr(). strstr() takes as its first argument a string to be searched (often called the subject), and as its second the substring to search for (often called the search pattern). If strstr() succeeds, it will return the searched for substring and all text following it; otherwise, it returns false. Here is a use of strstr() to determine whether the word PHP appears in the string $string: if(strstr($string, ‘PHP’) !== FALSE) { // do something } If you want to search for a substring irrespective of case, you can use stristr(). Here is a check to see if any forms of ‘PHP’ (including ‘php’, ‘Php’, and so on) appear in $string: if(stristr($string, ‘PHP’) !== FALSE) { // do something } If instead of the actual string you would like the position of the match returned to you, you can use strpos(). strpos() works similarly to strstr(), with two major differences: n Instead of returning the substring containing the match, strpos() returns the character offset of the start of the match. n strpos() accepts an optional third parameter that allows you to start looking at a particular offset. Here is a sample usage of strpos() to find every starting position of the substring ‘PHP’ in a search subject $string. 06 7090 ch05 7/16/04 8:42 AM Page 92 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. 93 Formatting Strings $offset = 0; $match_pos = array(); while(($offset = strpos($string, ‘PHP’, $offset)) !== FALSE) { $match_pos[] = $offset; } strpos() also has a not case-sensitive form, stripos(), that behaves in a similar fashion. Tip Because the first character in a string is at position 0, you should always use === to test whether a match from strpos() succeeded or failed. If you need to match from the end of your subject backwards, you can do so with strchr(), strrpos(), or strripos(). strrpos() and strripos() behave identically to strpos() and stripos() with the exception that they start at the end of the subject string and that the search pattern can only be a single character. strrchr() behaves like strstr(), returning the matched character and the rest of the subject following it, but it also requires a single character search pattern and operates starting at the end of the sub- ject (this is in contrast with the majority of strr* functions, which take full strings for all their arguments). Formatting Strings Specifying specific formats for strings is largely a leftover from compiled languages such as C, where string interpolation and static typing make it more difficult to take a collec- tion of variables and assemble them into a string. For the most part, PHP will do all of this for you. For example, most string formatting looks like this: $name = ‘George’; $age = 30; print “$name is $age years old.”; When variables are placed inside a double-quoted string, they are automatically expand- ed. PHP knows how to convert numbers into strings as well, so $age is correctly expanded as well. Occasionally, however, you need to perform more complex formatting.This includes the padding of numbers with 0s (for example, displaying 05 instead of 5), limiting the printed precision of floating point numbers, forcing right-justification, or limiting the number of characters printed in a particular string. printf Formats The basic function for formatting is printf(). printf() takes a format string and a list of arguments. It then passes through the formatting string, substituting special tokens contained therein with the correctly formatted arguments. 06 7090 ch05 7/16/04 8:42 AM Page 93 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. [...]... spammers) by performing the following substitution: $new_subject = preg_replace(“/(\S+)@(\S+)/”, ‘\1 at \2’, $subject); This code will convert addresses such as ‘license @php. net’ to ‘license at php. net’ Splitting Strings into Components PHP provides you three main options for taking a string and separating it into components: explode(), split(), and preg_split() Please purchase PDF Split-Merge on www.verypdf.com... via a form), complex data is often packed into strings and needs to be extracted Common examples include decomposing phone numbers, credit card numbers, and email addresses into their base components PHP provides both basic string functions for efficiently extracting data in fixed formats, as well as regular expression facilities for matching more complex data Please purchase PDF Split-Merge on www.verypdf.com... expressions (often abbreviated regexps) Regular expressions provide a robust language for specifying patterns in strings and extracting or replacing identified portions of text Regular expressions in PHP come in two flavors: PCRE and POSIX PCRE regular expressions are so named because they use the Perl Compatible Regular Expression library to provide regexps with the same syntax and semantics as those... Extracting Data from Strings Optionally, a different character can be specified by escaping it with a ‘ So to pad all your numbers with xxx, you would use printf(“%’xd”, $number); printf() Family Functions PHP has a small collection of formatting functions that are differentiated from each other by how they take their arguments and how they handle their results The basic function (which you saw previously)... whitespace) 3 Which of the following functions is most efficient for substituting fixed patterns in strings? A preg_replace() B str_replace() C str_ireplace() D substr_replace() Answer B is correct.The PHP efficiency mantra is “do no more work than necessary.” Both str_ireplace() and preg_replace() have more expensive (and flexible) matching logic, so you should only use them when your problem requires . is a check to see if any forms of PHP (including php , Php , and so on) appear in $string: if(stristr($string, PHP ) !== FALSE) { // do something } If. example, PHP is a substring of the string PHP is a scripting language. Matching Leading Substrings To match only the leading portion of strings, PHP provides