Common-Description:
 GDB, the GNU Project debugger, allows you to see what is going on `inside'
 another program while it executes -- or what another program was doing at the
 moment it crashed.
 .
 GDB can do four main kinds of things (plus other things in support of these) to
 help you catch bugs in the act:
 .
   * Start your program, specifying anything that might affect its behavior.
   * Make your program stop on specified conditions.
   * Examine what has happened, when your program has stopped.
   * Change things in your program, so you can experiment with correcting the
     effects of one bug and go on to learn about another.