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

554 Chapter 26 Debugging
This warning makes it very easy to correct. Few people would try to write code that
attempted to divide by zero on purpose, but neglecting to check user input often results
in this type of error.
The following code sometimes generates the same error but might be much harder to
isolate and correct because it happens only some of the time:
$i = 10;
$k = $i/$_REQUEST['input'];
This is one of many different runtime errors that you might see while testing your code.
Common causes of runtime errors include the following:
n Calls to functions that do not exist
n Reading or writing files
n Interaction with MySQL or other databases
n Connections to network services
n Failure to check input data
We briefly discuss each of these causes in the following sections.
Calls to Functions That Do Not Exist
Accidentally calling functions that do not exist is easy.The built-in functions are
often inconsistently named.Why does strip_tags() have an underscore, whereas
stripslashes() does not?
It is also easy to call one of your own functions that does not exist in the current
script but might exist elsewhere. If your code contains a call to a nonexistent function,
such as
nonexistent_function();
or
mispeled_function();
you will see an error message similar to this:
Fatal error: Call to undefined function: nonexistent_function()
in /home/book/public_html/phpmysql4e/chapter26/error.php on line 1
Similarly, if you call a function that exists but call it with an incorrect number of parameters,
you will receive a warning.
The function strstr() requires two strings: a haystack to search and a needle to find.
If instead you call it using
strstr();
you will get the following warning:
Warning: Wrong parameter count for strstr() in
/home/book/public_html/phpmysql4e/chapter26/error.php on line 1