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debugging tool
(foldoc) | debugger
debugging tool
A tool used by a programmer to monitor
and control a program he is trying to fix. The most important
functions of a debugger are tracing, stepping, breakpoints and
watches.
Tracing displays a step-by-step report on what statement the
program is currently executing, allowing the programmer to follow
the flow of control through if statements, loops (loop),
subroutine calls, etc.
Breakpoints and watches both pause execution of the program
and return control to the debugger under certain conditions. A
breakpoint triggers when execution reaches a particular
statement in the program and a watch triggers whenever a
specific variable is modified. Stepping is like a breakpoint on
every statement, often with the option to step "into" or "over" a
subroutine, i.e. continue stepping through the statements of the
subroutine or just execute it without pausing and resume stepping
when it returns.
Whenever control returns to the debugger it lets the programmer
ask to see the values of variables, and possibly modify them,
before resuming execution. Some debuggers can be set to
automatically perform some action like display a variable value
and resume.
A debugger can interact with the target program in different ways.
Some debuggers require the program to be loaded into the debugger
which may then modify or "instrument" the program for debugging.
Others can "attach" to a program that is already running. Some
are built into the normal program execution environment (e.g. an
interpreter) and can be set to run under certain conditions,
e.g. errors.
Early debuggers such as Unix's adb only knew about the
compiled executable code so sometimes debugging had to be done at
the level of machine code instructions and numerical memory
locations. If you were lucky, the debugger could access the
program's symbol table and display the original names of
subroutines and variables. Sometimes this required the program to
be "compiled for debugging". Since compiling every program for
debugging would add significantly to the size of a distribution
of a whole operating system, it is common for programs to be
distributed without debugging support but for individual programs
to be made available with it.
A major advance in debuggers was source-level debugging. This
gives the programmer a view of their source code annotated with
breakpoints and a pointer to the statement currently being
executed. Such a view is commonly part of an {integrated
development environment} like Visual Basic.
(2014-08-23)
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