   The purpose of a debugger such as GDB is to allow 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.

Homepage:
https://www.gnu.org/software/gdb/gdb.html
