Laboratory Exercises, C++ Programming

Tools for Practical C++ Development 17
(gdb) next
10 double r = reciprocal(i);
If you want to see what is going on inside reciprocal, step into the function with step:
(gdb) step
reciprocal (i=5) at reciprocal.cc:5
5 return 1.0 / i;
The next statement to be executed is the return statement. Check the value of i and then issue
the continue command to execute to the next breakpoint (which doesn’t exist, so the program
terminates):
(gdb) print i
$2 = 5
(gdb) continue
Continuing.
argv[1] = 5, 1/argv[1] = 0.2
Program exited normally.
A5. Try the debugger by working through the example. Experiment with the commands (the
table below gives short explanations of some useful commands). Commands may be
abbreviated and you may use tab for command completion. Ctrl-a takes you to the
beginning of the command line, Ctrl-e to the end, and so on. Use the help facility and the
manual if you want to learn more.
help [command] Get help about gdb commands
run [args...] Run the program with arguments specified.
continue Continue execution.
next Step to the next line over called functions.
step Step to the next line into called functions.
where Print the call stack.
up Go up to caller.
down Go down to callee.
list [nbr] List 10 lines around the current line or around line nbr (the
following lines if repeated).
break func Set a breakpoint on the first line of a function func.
break nbr Set a breakpoint at line nbr in the current file.
catch [arg] Break on events, for example exceptions that are thrown or caught
(catch throw, catch catch).
info [arg] Generic command for showing things about the program, for
example information about breakpoints (info break).
delete [nbr] Delete all breakpoints or breakpoint nbr.
print expr Print the value of the expression expr.
display var Print the value of variable var every time the program stops.
undisplay [nbr] Delete all displays or display nbr.
set var = expr Assign the value of expr to var.
kill Terminate the debugger process.
watch var Set a watchpoint, i.e., watch all modifications of a variable. This
can be very slow but can be the best solution to find bugs when
”random” pointers are used to write in the wrong memory location.