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GDB
contains a large repertoire of commands. See Debugging with GDB,
for extensive documentation on the use
of these commands, together with examples of their use. Furthermore,
the command help invoked from within GDB activates a simple help
facility which summarizes the available commands and their options.
In this section we summarize a few of the most commonly
used commands to give an idea of what GDB
is about. You should create
a simple program with debugging information and experiment with the use of
these GDB
commands on the program as you read through the
following section.
set args
argumentsset args
command is not needed if the program does not require arguments.
run
run
command causes execution of the program to start from
the beginning. If the program is already running, that is to say if
you are currently positioned at a breakpoint, then a prompt will ask
for confirmation that you want to abandon the current execution and
restart.
breakpoint
locationGDB
will await further
commands. location is
either a line number within a file, given in the format file:linenumber
,
or it is the name of a subprogram. If you request that a breakpoint be set on
a subprogram that is overloaded, a prompt will ask you to specify on which of
those subprograms you want to breakpoint. You can also
specify that all of them should be breakpointed. If the program is run
and execution encounters the breakpoint, then the program
stops and GDB
signals that the breakpoint was encountered by
printing the line of code before which the program is halted.
breakpoint exception
nameprint
expressionGDB
, so the expression
can contain function calls, variables, operators, and attribute references.
continue
step
next
list
backtrace
up
GDB
can display the values of variables local
to the current frame. The command up
can be used to
examine the contents of other active frames, by moving the focus up
the stack, that is to say from callee to caller, one frame at a time.
down
GDB
down from the frame currently being
examined to the frame of its callee (the reverse of the previous command),
frame
nThe above list is a very short introduction to the commands that
GDB
provides. Important additional capabilities, including conditional
breakpoints, the ability to execute command sequences on a breakpoint,
the ability to debug at the machine instruction level and many other
features are described in detail in Debugging with GDB. Note that most commands can be abbreviated
(for example, c for continue, bt for backtrace).