Error Handling

BBj uses a trap-and-branch model for error handling: you set error traps (SETERR, ERR=) that redirect execution when errors occur, and raise errors with THROW. This pattern is used throughout all BBj code -- understanding it is essential before writing anything non-trivial.

At a Glance

Feature	Syntax	Purpose
SETERR	seterr label	Set global error trap
ERR=	open(1,err=handler)"file"	Statement-level error trap
THROW	throw "message", 256	Raise custom error
ERR	err	Last error number
ERRMES	errmes(-1)	Last error message
RETRY	retry	Re-execute the statement that errored

For Java, Python, and C# Developers

Task	Java	Python	C#	BBj
Set error handler	try {	try:	try {	seterr handler
Catch specific error	catch (IOException e)	except IOError as e:	catch (IOException e)	if err = 17 then ...
Catch all errors	catch (Exception e)	except Exception as e:	catch (Exception e)	seterr handler (global)
Get error message	e.getMessage()	str(e)	e.Message	errmes(-1)
Raise/throw	throw new Exception("msg")	raise Exception("msg")	throw new Exception("msg")	throw "msg", 256
Skip on error	catch (E e) { }	except: pass	catch { }	err=*next
Cleanup	finally { }	finally:	finally { }	Fall-through to cleanup label

BBj does not have try/catch blocks. All error handling uses seterr to set a handler label, err= on individual statements for inline trapping, and throw to raise custom errors. For the complete cross-language reference, see BBj for Java, Python, and C# Developers.

Complete Runnable Examples

This chapter's code snippets illustrate individual concepts. For complete, runnable programs you can open directly in the BBj IDE, see the sample files in samples/04-error-handling/:

• seterr_basic.bbj -- Basic SETERR error trapping
• err_clause.bbj -- ERR= clause on individual statements
• throw_validation.bbj -- THROW from a class method
• java_error_handling.bbj -- Handling Java exceptions in BBj

See Running Samples for setup instructions.