As a final step, you can add the following code to the beginning of
the script to enable all possible error and warning messages. The PHP
scripting engine is very good at locating syntax and run-time errors,
so you should use it whenever possible. Sometimes, the PHP script-
Ing engine can even help locate logic errors.
// DEBUG: Show all warnings
error_reporting(E_ALL | E_STRICT);
When you finish, your code should look like the following:
// DEBUG: Show all warnings
error_reporting(E_ALL | E_STRICT);
$TerritorialCapitals = array(
array("Territory" => "Nunavut",
"Capital" => "Iqaluit"),
array("Territory" =>
"Northwest Territories",
"Capital" => "Yellowknife"),
APPENDIX
E
array("Territory"
=>
"Yukon Territory",
"capital" => "Whitehorse"));
// DEBUG: Verifying $TerritorialCapitals
echo "<pre>\n";
echo "\$TerritorialCapitals => ";
print_r($TerritorialCapitals);
echo "</pre>\n";
// DEBUG: End verifying $TerritorialCapitals
$TerritoryCount=count($TerritorialCapitals);
// DEBUG: Verifying $TerritoryCount
echo "<p>\$TerritoryCount = " .
$TerritoryCount . "</p>\n";
for ($i=1;$i<=$TerritoryCount;++$i) {
// DEBUG: Verifying $i
echo "<p>In for loop: \$i = " .
$i . "</p>\n";
echo "<p>" . $TerritorialCapitals[$i]["Capital"] .
" is the capital of " .
$TerritorialCapitals[$i]["Territory"] .
"</p>\n";
}
668
When you run the script this time, much more information is avail-
able to you. First, examine the XHTML source code, as shown in
Figure E-4. Although the debugging has created extra code, you
should be able to find the lines that display the names of the territo-
ries and capitals. Review those lines to see what data is actually miss-
ing. This is important because Web browsers often do not display data
that is embedded in malformed tags. Without looking at the source
code, you cannot tell if the data is actually missing or just hidden.
Figure E-4
Source code for a PHP script with debugging statements
Now that you’ve confirmed that the data is actually miss-
ing, you can review the debugging information available on the
APPENDIX
E
page
itself, as shown in Figure E-5. At the top of the page, the
$TerritorialCapitals[]
array
is populated as expected. The next
message
indicates that the $TerritoryCount
variable
is set to 3.
669
Figure
E-5
Web
page for a PHP script with debugging statements
APPENDIX
E
670
In
the next line, you can see that $i
is
set to 1 and that Yellowknife is
displayed
as the capital of the Northwest Territories. The array output
at
the beginning of the page shows that the array index for the ele-
ment
with "Northwest
Territories" and
"Yellowknife"
is
indeed
1.
The array index for "Nunavut"
and
"Iqaluit"
is
0. So, to display
Nunavut,
you need to adjust the starting value of $i
to
0.
Next,
you see that $i
gets
incremented to 2, which is expected.
After
that, the PHP scripting engine displays a notice that the index
Capital
is
undefined. By looking at the array output, you can see that
for
$TerritorialCapitals[2],
the index of the nested array element
is
"capital"
with
a lowercase ‘c’. Change this to an uppercase ‘C’.
After
displaying the line with the missing capital, you see that $i
is
set
to
3, followed by two warning messages about an undefined offset of
3.
Look at the lines identified by the message, and note that these
two
lines
display the values of the $TerritorialCapitals[]
array.
Again,
look
back to the array output, and note that the last array element is
2,
not 3. To fix this, you need to change the comparison in the for
loop
from $i<=$TerritoryCount
to
$i<$TerritoryCount.
After
making the three changes to the code and removing all of the
debugging
statements, run the script again. You will see the expected
results,
as shown in Figure E-6. By using a combination of debugging
techniques,
you found and fixed all of the errors much faster and
more
easily than if you had applied a single technique.
Figure
E-6
Output
from a PHP script with the errors fixed