gdb.info: Setting

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Switching between source languages

There are two ways to control the working language--either have GDB set
it automatically, or select it manually yourself.  You can use the `set
language' command for either purpose.  On startup, GDB defaults to
setting the language automatically.  The working language is used to
determine how expressions you type are interpreted, how values are
printed, etc.
   In addition to the working language, every source file that GDB
knows about has its own working language.  For some object file
formats, the compiler might indicate which language a particular source
file is in.  However, most of the time GDB infers the language from the
name of the file.  The language of a source file controls whether C++
names are demangled--this way `backtrace' can show each frame
appropriately for its own language.  There is no way to set the
language of a source file from within GDB, but you can set the language
associated with a filename extension.  *Note Displaying the language:
Show.
   This is most commonly a problem when you use a program, such as
`cfront' or `f2c', that generates C but is written in another language.
In that case, make the program use `#line' directives in its C output;
that way GDB will know the correct language of the source code of the
original program, and will display that source code, not the generated
C code.