Manual Debugging
As was mentioned earlier, once you get a few good years of development time under your belt, you should be able to get at least 75% of your debugging done on a purely visual basis. What of the other 25%, and the more difficult segments of code that you need to work through? Some of this can be alleviated by using a great code development environment like Zend Studio for Eclipse or Komodo. These advanced IDEs can help with syntax checking and some simple code logical problems and warnings.
The next level of debugging can be done (again, most of this will be
done in the development environment) by echoing values out onto the
screen. This will catch a lot of logic errors that may be dependent on the
contents of variables. For example, how would you easily be able to see
the value of the third iteration of a for...next
loop? Consider the following
code:
for
(
$j
=
0
;
$j
<
10
;
$j
++
)
{
$sample
[]
=
$j
*
12
;
}
The easiest way is to interrupt the loop conditionally and
echo
out the value at the time;
alternatively, you can wait until the loop is completed, as in this case
since the loop is building an array. Here are some examples of how to
determine that third iteration value (remember that array keys start with
0):
for
(
$j
=
0
;
$j
<
10
;
$j
++
)
{
$sample
[]
=
$j
*
12
;
if
(
$j
==
3
)
{
echo
$sample
[
2
];
}
}
24
Here we are simply inserting a test (if
statement) that will send a particular value to the browser when that condition is met. If you are having SQL syntax problems or failures, ...
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