PHP Using Strings

1. PHP Using Strings

2. Note • There are many PHP functions available for arrays and for strings. • You will only be responsible for those presented in class. • You may use others you find in PHP references for your homework assignments. • (http://www.php.net/string - string type, http://us2.php.net/manual/en/ref.strings.php - string functions, http://us2.php.net/manual/en/book.pcre.php - Perl-compatible regular expressions)

3. Strings • Topics: • Formatting strings: trimming, for presentation, for storage • Joining and splitting strings with string functions • Comparing strings • Matching and replacing substrings with string functions • Using regular expressions

4. Strings • Recall: • String literals: • delimited by double or single quotes, • in heredoc syntax (creates a large text string without needing quotes, and can be used anyplace a string would go) <<<DONE your_string_here on_multiple_lines_until closing_identifier DONE • or nowdoc syntax • Interpolation of variables in double-quoted and heredoc strings • The string concatenation operator, “.“

5. Formatting Strings - trimming • Several functions are available to tidy up strings before using them – especially user strings from an HTML form interface • Trimming strings = removing any excess whitespace • string trim(string $str [, string $charlist]) Strips whitespace (spaces, newlines \n, carriage returns \r, horizontal tabs \t, end-of-string characters \0) from the start and end of string $str Use the second optional parameter to indicate a list of characters to strip instead of the default list (=whitespace) Creates new string! • ltrim(…) and rtrim(…) are similar to trim(), but remove whitespace only from the start /left (ltrim) or end/right (rtrim) of the string • Ex: collecting feedback for Bob’s auto parts → clean the user input, trimming it is a first step

6. Formatting Strings - printing • 3 basic methods: • language construct echo • Prints a comma-separated series of strings • Can enclose string in parentheses for single string only • language construct print • Prints a single string – which can be enclosed in parentheses or not • Returns T/F to indicate if it was successful • function printf( ) – formats and prints a string • Just like C printf • First argument is a format string, the rest are variables to be formattedand interpolated; see next • The sprintf() function is similar, except that it returns the formatted string instead of printing it to the browser • All printing is output to the browser.

7. Formatting Strings - printf • The functions printf() and sprintf () provide a means for formatting strings • They will be familiar to C programmers • They are a bit “messy” and we will cover only briefly for a few basic capabilities • printf() is used to format and then print a string • Just use as printf(….); • sprintf() formats into a new string rather than printing it • Use as $newStr = sprintf(….);

8. Formatting Strings - printf • Both subroutines take a format string and a list of variablesprintf($fmt_str, $a, $b, $c, …); • The format string contains: • characters to be printed as they are and • special characters to describe how the following variables are to be interpolated (= substituted) into the format string • you can format several variables into a printf() by including several format specifications, (normally) one for each variable specified: → the format specifications should be in the same number as the variables to format → the ith format specification is applied to the ith variable

9. Formatting Strings - printf • The format specifications (or conversion specifications): • Start with the % character • An optional “–” indicates the data in the field is left-justified (rather than right-justified, which is the default) • Letters are used to designate the data type to be printed (floating point value - f, decimal number - d, string - s, character - c, etc.) • Numbers between the % and the format type character give field sizes: • First number is total size (width), • Second number (if any) gives the number of decimal places to display (precision), • Numbers separated by a period. • Q: %10s, %6d, %5.2f ?

10. Formatting Strings - printf • Example: to format for currency • Data type is “float” (f) • Number of digits before decimal point is 5 • Number of digits after decimal point is 2 • Format specification is %8.2d printf(“Your total is \$%8.2f\n”, $total); If $total is 123.4567, prints “Your total is $123.46” • Example: printf(“%4d and %5.3f”, $a, $b); If $a is 1.23 and $b is 4.56, prints “1 and 4.560” • There are far too many options to describe them all here. • Read your textbook or review your Java text for more details

11. Formatting Strings – presentation • HTML formatting: string nl2br(string $str) • Replaces all the new line characters in $str with XHTML <br /> tags • Creates a new string • Useful when echoing a long string to the browser • Example: $sfweather = “<p><strong>San Francisco daily weather forecast</strong>: \n Today: \n Partly cloudy. Highs from the 60s to mid 70s. West winds 5 to 15 mph. \n Tonight: \n Increasing clouds. Lows in the mid 40s to lower 50s. West winds 5 to 10 mph.</p>”; echo $sfweather; // the browser disregards plain whitespace //  everything on a single line except for newlines forced by the browser window echo nl2br($sfweather); // each newline character is replaced with <br />

12. nl2br.php • http://www.nku.edu/~frank/csc301/Examples/PHP_Strings/nl2br.php • http://www.nku.edu/~frank/csc301/Examples/PHP_Strings/nl2br_php.pdf

13. Formatting Strings – presentation • Changing the case of a string: • string strtoupper (string $str) – turns string to uppercase • string strtolower (string $str) – turns string to lowercase • string ucfirst (string $str) – capitalizes 1st character of the string if it’s alphabetic • string ucwords(string $str) – sets 1st character in each word that begins with an alphabetic character to upper case • For each of these functions: • The argument is a string • Function creates a new string

14. Formatting Strings – for storage • Reason – certain characters • are valid as part of a string but • can cause problems when are inserted into a database because are interpreted by the DBMS as control characters • Ex: single and double quotation marks, backslash • Solution: escape those characters by adding a backslash in front of them: ” → \”, \ → \\ • how: string addslashes(string $str)returns the reformatted $str string • Conversely: • string stripslashes(string $str)returns a copy of the $str string from which the escape characters have been removed

15. Formatting Strings – for storage • Before applying addslashes() check if magic_quotes_gpc configuration directive is turned on • With magic_quotes_gpc on, all variables coming from GET, POST and cookie are automatically escaped  applying addslashes() would cause double-escaping • boolean get_magic_quotes_gpc() returns T if magic_quotes_gpc is on; F otherwise • phpinfo() displays magic_quotes_gpc directive’s value, among other information • magic_quotes_gpc is currently off on cscdb

16. slashes • http://www.nku.edu/~frank/csc301/Examples/PHP_Strings/quotes.php • http://www.nku.edu/~frank/csc301/Examples/PHP_Strings/quotes_php.pdf

17. Joining & splitting strings with string functions • array explode (string $separator, string $input [, int $limit]) • Splits $input into pieces on a specified $separator string • Pieces are returned in an array • The number of pieces can be limited to $limit. • Example: $email = ‘campana1@nku.edu’; $email_array = explode(‘@’, $email); // email_array[0] contains the username (campana1) // email_array[1] contains the domain name (nku.edu) // actions can be decided upon customer’s origin as indicated by the domain name • string implode (string $glue, array $pieces) → opposite to explode() • Joins array elements from $pieces with string $glue • join() is identical to implode()

18. Joining & splitting strings with string functions • string strtok(string $input, string $separator) • Gets tokens (pieces) from $input one at a time • Splits $input on each of the characters in $separator rather than on the whole separator (as explode() does) • Usage: // first token extracted with a call to strtok() with both parameters $token = strtok($feedback, " ,."); // subsequent calls automatically apply to the same string; // only separator is passed to strtok() // strtok() maintains its internal pointer to its current place in the string // reset the pointer by calling again strtok() with two parameters while ($token != "") { echo "$token <br />"; $token = strtok(" ,."); }

19. http://www.nku.edu/~frank/csc301/Examples/PHP_Strings/strtok.phphttp://www.nku.edu/~frank/csc301/Examples/PHP_Strings/strtok.php • http://www.nku.edu/~frank/csc301/Examples/PHP_Strings/strtok_php.pdf

20. Joining & splitting strings with string functions • string substr(string $str, int $start[,int $length]) • Called with 1 positive argument (start): returns the substring of $str from the $start position to the end of the string • Called with 1 negative argument (start): returns the substring of $str from the end of the string - |$start| characters to the end of the string • Called with 2 arguments (start and length): • If $length is positive: specifies the number of characters to return starting from position $start • If $length is negative: function returns the substring from $start position to the end of the string - |$length | position • Note: string position starts at 0 • Extracting a single character: $string{$index} • $index is 0-based character count from start of string

21. Comparing Strings • Use == and === for exact compare • Use strcmp(…) for ordered compare: • int strcmp(string $str1, string $str2) • Returns <0 if $str1 sorts before $str2 (= $str1 is less than $str2) in lexicographic order • Returns >0 if $str2 sorts before $str1 in lexicographic order • Returns 0 if $str1 and $str2 are the same in lexicographic order • strcmp(…) is case-sensitive

22. Comparing Strings • strncmp(… ) • Similar to strcmp(…), • Has 3rd argument: number of characters to compare (if < strings’ length) • Use int strlen(string $str) to get the length of a string