PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

120 Chapter 4 String Manipulation and Regular Expressions
Testing String Length with strlen()
You can check the length of a string by using the strlen() function. If you pass it a
string, this function will return its length. For example, the result of code is 5:
echo'strlen("hello");.
You can use this function for validating input data. Consider the email address on the
sample form, stored in $email. One basic way of validating an email address stored in
$email is to check its length. By our reasoning, the minimum length of an email address
is six characters—for example, a@a.to if you have a country code with no second-level
domains, a one-letter server name, and a one-letter email address.Therefore, an error
could be produced if the address is not at least this length:
if (strlen($email) < 6){
echo ‘That email address is not valid’;
exit; // force execution of PHP script
}
Clearly, this approach is a very simplistic way of validating this information.We look at
better ways in the next section.
Matching and Replacing Substrings with String
Functions
Checking whether a particular substring is present in a larger string is a common operation.This
partial matching is usually more useful than testing for complete equality in
strings.
In the Smart Form example, you want to look for certain key phrases in the customer
feedback and send the mail to the appropriate department. If you want to send emails
discussing Bob’s shops to the retail manager, for example, you want to know whether the
word shop or derivatives thereof appear in the message.
Given the functions you have already looked at, you could use explode() or
strtok() to retrieve the individual words in the message and then compare them using
the == operator or strcmp().
You could also do the same thing, however, with a single function call to one of the
string-matching or regular expression-matching functions.They search for a pattern
inside a string. Next, we look at each set of functions one by one.
Finding Strings in Strings: strstr(), strchr(), strrchr(),
and stristr()
To find a string within another string, you can use any of the functions strstr(),
strchr(), strrchr(), or stristr().