Generating Debug Output

If your CFX tag encounters any problems during its execution, or if you need help figuring out why your tag isn’t doing what you expect it to, you can have your tag include debug messages in the calling template. Debug messages can include whatever text you want; usually you use them to display some kind of diagnostic information that indicates whether the tag was able to connect to some kind of data source, was denied access to some kind of file, or encountered some other type of unexpected condition.

In the <CFX_ComputeStandardDeviation> example, the tag is expecting to find only numbers in the query column passed to the tag. It knows to skip over null values, and generally does so silently. But since it’s avoiding a potential problem, you might want to be able to see which values are being skipped over. The code in Listing 79.6 uses the following lines to output debug messages: