Debugging

BBj provides a powerful console-based debugging environment that lets you break into a running program, step through code line by line, inspect and modify variables, and trace execution to a file. These tools work directly in the BBj interpreter -- no IDE plugin required.

At a Glance

Technique	Command/Verb	Purpose
Break to console	Ctrl-C or Ctrl-Break	Pause running program
Single step	. + Enter	Execute one line
Step over	.. + Enter	Execute one line, skip subroutine internals
Step N lines	. n	Execute next n lines
Print variable	? var or PRINT var	Display variable value
Change variable	var = newvalue	Modify variable at runtime
Search code	\searchstring	Find text in program
DUMP	DUMP(chan)	Write all variables to file
SETTRACE	SETTRACE(chan)	Log each executed line to file
ENDTRACE	ENDTRACE	Stop tracing

BBj debugging is interactive. You are inside the running interpreter with full access to program state. You can evaluate expressions, call methods, and even change code flow -- the console is a live REPL in the context of your paused program.

For Java, Python, and C# Developers

Task	Java	Python	C#	BBj
Print debug	System.out.println(x)	print(x)	Console.WriteLine(x)	print x
Set breakpoint	IDE breakpoint or assert	breakpoint()	IDE breakpoint	Ctrl-C or Ctrl-Break at runtime
Trace execution	-verbose flag or debugger	sys.settrace(fn)	Debugger step-through	SETTRACE(chan) to log each line
Inspect variable	Debugger watch window	pdb: p variable	Debugger watch window	? var in console
Dump all variables	Heap dump	locals()	Debugger locals window	DUMP(chan) to file

BBj's debugger is built into the interpreter console -- no IDE plugin required. You break into a running program and interact with it as a live REPL. 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/11-debugging/:

• settrace_example.bbj -- SETTRACE/ENDTRACE to record line-by-line execution
• dump_example.bbj -- DUMP verb to write all variables to a file
• logging_example.bbj -- System.out.println and PRINT-based logging techniques

See Running Samples for setup instructions.