The Additional Topics give some general considerations about accessing
  program variables while debugging.

  If your program was optimized during compilation, you might not have
  access to certain variables while debugging.  When you compile a
  program for debugging, it is best to disable optimization, if possible.

  Before you check on the value of a variable, always execute the program
  beyond the point where the variable is declared and initialized.  The
  value contained in any uninitialized variable should be considered
  invalid.