throw Statement

throw statements are how errors are raised in TMBASIC. Once an error is raised, it can be handled by a try ... catch block. Use rethrow in your catch block to re-raise an error that you want to pass up to the calling code.

An error has a message and an optional numeric code. All TMBASIC system errors have numeric codes, but for user errors the numeric code is optional.

Syntax

throw <ERROR-MESSAGE>

throw <ERROR-CODE>, <ERROR-MESSAGE>

<ERROR-MESSAGE> is a string containing the human-readable error message.
<ERROR-CODE> is a numeric error code. This is optional, and defaults to 0 if not specified.

Usage

The following example is contrived to show both the "thrower" and "catcher" sides of a raised error. The message string provided to the throw statement can be retrieved from the ErrorMessage function inside your catch block. The ErrorCode function can be used to retrieve the error code, which is optional for your own throw statements but is always available for TMBASIC-generated errors.

try

throw 1234, "This is an error!"

catch

print ErrorCode(); ": "; ErrorMessage()

end try

In real code, the throw statement will be inside a function or subroutine, and the catch block will be in the calling code.