GDB: an introduction

gdb (GNU DeBugger) is invaluable for debugging large C/C++ programs.
gdb adds the debugging power of an interpreted language to C/C++.
There is also a graphical version, ddd (which appears not to work
  on CCIS Solaris machines as of Sept., 2004?).

For Java, there is also a somewhat less mature cousin, jdb.
Another alternative for Java is to use GNU gcj to compile the
programs and GNU gdb (version 5.1 or greater) to debug the program.
A tutorial for gdb/gcj is at:  http://www.gnu.org/software/gcc/java/gdb.html

To use gdb, you should first re-compile your source code using
the `-g' flag.  It is also helpful to also use `-O0'  (optimize
at level zero), since otherwise an optimization may delete or move
a line of source code.  Note that a program compiled with `-O0'
runs more slowly.  For production, recompile without `-O0'.
  gcc -g -O0 myfile.c
  g++ -g -O0 myfile.c

Then type:
  gdb a.out

These are some basic techniques available throughout gdb:
  <TAB> completion
  <RETURN> repeat last command
  arrow keys (cursor keys) works
  Most gdb commands can be abbreviated.  Try the abbreviations:
    e.g.: n = next, s = step, c = continue, p = print, ...

The most important commands in gdb are (roughly in order of importance):
  RUN AND EXAMINE BUG:  help, run, where, list, up, down, print, ptype
  SET BREAKPOINT AND STEP THROUGH:
			help breakpoints, break, next, step, finish, continue

=====================================================================
EXAMPLES OF USAGE:
help
help breakpoints

break main
run 1234 > myfile.out  [ Anything after `run' is as if it's on
			 the command line of a call to `a.out' ]
next   (next line)
step   (step inside next function, or next line if no function)
finish  (finish current function, and stop for commands)
list     (list lines around current line number)
list main
print x
print x+3
print *(int *)ptr
print foo(3)  (execute foo(3) and display the result)
ptype ptr     (print type of variable)
break <line number>
break main    (Add breakpoint at beginning of routine main)
  For C++, note
    gdb 'MyClass::myfnc(<TAB>
  to see all possible member functions for the method MyClass::myfn
run           (kill current process, start a new one)
continue (continue until next breakpoint)
^C (control-C)   (Type this if in an infinite loop, and GDB will stop
			the process at some line number.)
quit

ADVANCED COMMANDS:
watch, awatch, rwatch   (slower, because tested at every line)

attach <pid>   (attach to a running process.  Useful for debugging
		client/server or master/worker applications.)
detach