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(g77-295.info)Ugly Null Arguments

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Ugly Null Arguments
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   The `-fugly-comma' option enables use of a single trailing comma to
mean "pass an extra trailing null argument" in a list of actual
arguments to an external procedure, and use of an empty list of
arguments to such a procedure to mean "pass a single null argument".

   (Null arguments often are used in some procedure-calling schemes to
indicate omitted arguments.)

   For example, `CALL FOO(,)' means "pass two null arguments", rather
than "pass one null argument".  Also, `CALL BAR()' means "pass one null
argument".

   This construct is considered "ugly" because it does not provide an
elegant way to pass a single null argument that is syntactically
distinct from passing no arguments.  That is, this construct changes
the meaning of code that makes no use of the construct.

   So, with `-fugly-comma' in force, `CALL FOO()' and `I = JFUNC()'
pass a single null argument, instead of passing no arguments as
required by the Fortran 77 and 90 standards.

   *Note:* Many systems gracefully allow the case where a procedure
call passes one extra argument that the called procedure does not
expect.

   So, in practice, there might be no difference in the behavior of a
program that does `CALL FOO()' or `I = JFUNC()' and is compiled with
`-fugly-comma' in force as compared to its behavior when compiled with
the default, `-fno-ugly-comma', in force, assuming `FOO' and `JFUNC' do
not expect any arguments to be passed.