Showing C Function Headings
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   To show in which functions differences occur for C and similar
languages, you can use the `-p' or `--show-c-function' option.  This
option automatically defaults to the context output format (
see Context Format.), with the default number of lines of context.  You
can override that number with `-C LINES' elsewhere in the command line.
You can override both the format and the number with `-U LINES'
elsewhere in the command line.

   The `-p' and `--show-c-function' options are equivalent to
`-F'^[_a-zA-Z$]'' if the unified format is specified, otherwise `-c
-F'^[_a-zA-Z$]'' (see Specified Headings.).  GNU `diff' provides
them for the sake of convenience.