C and C++ defaults
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   If you allow GDB to set type and range checking automatically, they
both default to `off' whenever the working language changes to C or
C++.  This happens regardless of whether you or GDB selects the working
language.

   If you allow GDB to set the language automatically, it recognizes
source files whose names end with `.c', `.C', or `.cc', and when GDB
enters code compiled from one of these files, it sets the working
language to C or C++.  See Having GDB infer the source language: Automatically, for further details.