Macromedia Coldfusion MX 7 Web Application Construction Kit

The ColdFusion debugging options are enabled or disabled via the ColdFusion Administrator, as explained in Chapter 3, "Accessing the ColdFusion Administrator."

TIP

You can restrict the display of debugging information to specific IP addresses. If you enable debugging, you should use this feature to prevent debugging screens from being displayed to your site's visitors.

CAUTION

At a minimum, the local host IP address (127.0.0.1) should be specified. If no IP address is in the list, debugging information will be sent to anyone who browses any ColdFusion page.

ColdFusion supports three different debugging modes. They all provide the same basic functionality, but with different interfaces.

Classic Debugging

The classic debugging interface appends debugging information to the end of any generated Web pages, as shown in Figure 17.7. The advantage of this format is that it doesn't use any complex client-side technology, so it's safer to use on a wide variety of browsers.

To select this option, select classic.cfm as the debug format in the ColdFusion Administrator.

NOTE

This is known as the classic format because it's the format supported in ColdFusion since the very first versions of the product.

Dockable Debugging

ColdFusion also features a powerful DHTML-based debugging interface. As seen in Figure 17.8, debug information is displayed in a tree control in a separate pop-up window, or docked to the output itself, as seen in Figure 17.9. The advantage of this format (aside from a much cleaner and easier-to-use interface) is that the debug output doesn't interfere with the page itself.

To select this option, select dockable.cfm as the debug format in the ColdFusion Administrator.

Dreamweaver Debugging

Debug output is also accessible from within Dreamweaver itself, as seen in Figure 17.10. Any ColdFusion page can be debugged from within Dreamweaver by clicking the Server Debug button on top of the Dreamweaver editor window, or selecting Server Debug from the View menu. Debug output is displayed in the Results panel below in a tree format.

Using Debugging Options

Regardless of how the debugging information is accessed (through any of the options just listed) you'll have access to the same information:

• Execution time, so you can locate poorly performing code.

• Database activity, so you can determine exactly what was passed to the database drivers (post any dynamic processing) and what was returned.

• Tracing information (explained below).

• Variables and their values.

As you move from page to page within your application, the debug output will provide insight into what's actually going on within your code.

NOTE

The exact information displayed in debug output is managed by options in the ColdFusion Administrator.

Using Tracing

In addition to all the invaluable information provided by the debugger, you may on occasion want to generate your own debug output. For example, you may want to:

• Check the values of variables within a loop.

• Determine which code path or branch (perhaps in a series of <cfif> statements) is being followed.

• Inspect SESSION or other variables.

• Check for the presence of expected URL parameters or FORM fields.

• Display the number of rows retrieved by a query.

This kind of information is useful in debugging logic problemsthose annoying situations where code is valid syntactically, but some logic flaw (or unexpected situation) is preventing it from functioning correctly.

To insert your own information in debug output, use the <cftrace> tag, which embeds trace information. <cftrace> takes a series of attributes (all optional) that let you dump variable contents, display text (dynamic or static), abort processing, and more. As seen in Figure 17.11, the generated trace output is included with the standard debug output (if that option is enabled in the ColdFusion Administrator).

To use <cftrace>, simply embed <cftrace> tags at strategic locations in your code. For example, if you're trying to figure out why variables are being set to specific values, use <cftrace> statements at the top of the page, before and after any <cfinclude> statements and any other statements that could set variable values, and so on.

To output simple text use the following <cftrace> syntax:

<cftrace text="Just before the cfinclude">

To display variable values, you could do the following:

<cftrace text="firstname at top of page" var="firstname">

Additional <cftrace> attributes allow for message categorization and prioritization, but the two examples here are usually all you need. By embedding <cftrace> blocks in your code you'll get a clear and systematic view into what happened, when, and why.