ITEC 325 2011spring ibarland

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ch05
String processing
chapter 5

From PHP Visual Quickstart Guide by Larry Ullman
Based on notes by Jack Davis (jcdavis@radford.edu)

• Concatenation

  • $s1 = "hello"; $s2 = "world"; $s3 = $s1 . $s2; // "helloworld"

  • $s3 = "$s1$s2"; // also "helloworld";
  • $s1 .= "world"; // also "helloworld" (s1 modified)

  • $n1 =44; $s1 = "age"; $newstr = $s1 . $n1; // (coerces number to string)

• Replace raw new-lines with br tags (think about reading text area contents):
  

  nl2br("abc\ndef\nghi"); // returns "abc<br />def<br />ghi"

  $someVar = nl2br("abc\ndef\nghi");
  (Or: someVar = nl2br($_POST['someInput']);
• Sanitizing string input from forms
  • htmlspecialchars
    turns certain HTML (well, XML) characters into an entity version
    usage: $str = htmlspecialchars($_POST['fieldname']);
    for example “<span>” into “&lt;span&gt;”
  • htmlentities tries to turns all special characters their entity versions: htmlentities("é”&heart;") = "&eacute;&rdquo;&heart;"). (Of course, it also handles the few essential characters that htmlspecialchars handles; since nowadays it's fine to have characters like é in the middle of your UTF-8 file / database, there isn't much occasion to use htmlentities. .
  • strip_tags()
    removes all HTML and PHP tags — something you want to do with text input.
    Inserted HTML tags would likely affect the rendered page from the server, using different formats etc.. More importantly, the client could insert javascript into input fields, which can be used to implement cross-site scripting attacks (XSS).
    
  • Encrypting and Decrypting Strings
    
    • crypt() function - encrypts strings (passwords)
      one-way encryption, no decryption possible (encrypted version of passwords is stored)
      $password = crypt($password);
    • mcrypt_encrypt(), which can be decrypted using mcrypt_decrypt()
      The Mycrypt module must be installed with the PHP module (more complex)
      
    • Many database functions have been built to perform encryption and decryption.
  • Substrings
    • strtok() (string-tokenize function)

      $inp = "John Smith"; $first = strtok($inp, ' '); # returns "John"

    • substr() function

      $inp = "Radford"; $newinp = substr($inp,0,5); # starting position, length (Radfo)

  • strlen() function

    $str = "abcdef"; $len = strlen($str); # returns 6

  • strcmp() “string compare”
    Returns positive, 0, or negative number, depending on which argument is larger.
    

    $str = "abc"; echo strcmp($str,"xyz"); # returns a negative number

    Think of it as being the difference of the two arguments.
  • strpos() returns the position of a substring within a source string
    $inp = "abcde"; strpos($inp,'cd'); # returns 2
  • str_replace() (case sensitive) and str_ireplace() (case insensitive)
    

    $name = "Larry E. Ullman"; $newname = str_ireplace('E.','Edward',$name); # Larry Edward Ullman

  • Many, many, many, more -- Check the reference manual.
  • Example of some string functions.
    ch05-string-examples.php
  • ch05-string-process-form.php

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©2010, Ian Barland, Radford University Last modified 2011.Feb.20 (Sun)

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