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

Using Functions in PHP
145
Calling an Undefined Function
If you attempt to call a function that does not exist, you will get an error message, as
shown in Figure 5.3.
Figure 5.3
This error message is the result of calling a function that
does not exist.
The error messages that PHP gives are usually very useful.The one in the figure tells
you exactly in which file the error occurred, in which line of the script it occurred, and
the name of the function you attempted to call.This information should make it fairly
easy to find and correct the problem.
Check these two things if you see this error message:
n Is the function name spelled correctly?
n Does the function exist in the version of PHP you are using?
You might not always remember how a function name is spelled. For instance, some
two-word function names have an underscore between the words, and some do not.
The function stripslashes() runs the two words together, whereas the function
strip_tags() separates the words with an underscore. Misspelling the name of a
function in a function call results in an error, as shown in Figure 5.3.
Some functions used in this book do not exist in PHP4 because this book assumes
that you are using PHP5. In each new version, new functions are defined, and if you are
using an older version, the added functionality and performance justify an upgrade.To
see when a particular function was added, you can check the online manual. Attempting
to call a function that is not declared in the version you are running results in an error
such as the one shown in Figure 5.3.