Using the gnu debugger, gdb.

Compile your program with the -g option, e.g.,
    g++ -g -Wall -Werror prog.cc
(for separate compilation compile each .cc file with the -g option, e.g.,
    g++ -g -c -Wall -Werror point.cc   )

Then run gdb with the executable file, e.g.,
    gdb a.out

Some gdb commands:

  run                    execute the program
  bt                     show a "backtrace," the call stack
  list                   list about 10 lines of code
  help                   get the help file
  print <x>              display the contents of variable <x>
  break <func>           stop execution on entrance to method <func>
  break  <num>           stop execution at line number <num>
  step                   execute one instruction
  next                   execute the next line (if, e.g., a function
                         call, execute the function)
  continue               continue execution of the program