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From: mwm@VACATION.VENARI.CS.CMU.EDU (Mark Maimone)
Newsgroups: comp.lang.fortran
Subject: Re: f2c bug
Message-ID: <1991Apr5.175633.18864@cs.cmu.edu>
Date: 5 Apr 91 17:56:33 GMT
References: <4846@dirac.physics.purdue.edu>
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Reply-To: mwm@VACATION.VENARI.CS.CMU.EDU (Mark Maimone)
Organization: Carnegie Mellon University
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In article <4846@dirac.physics.purdue.edu>, piner@maxwell.physics.purdue.edu (Richard Piner) writes:
|> Looks like I have found a little bug in f2c. Of course, it took a
|> routine from NR to break it. Here it is. Always double check code
|> before using it.

  [code illustrating REAL FUNCTION H being referenced before declared]

F2c compiles functions one at a time, sequentially.  During the first pass through the program, since H has only been declared EXTERNAL, f2c assumes that it refers to a subroutine rather than a function; how could it infer anything else?  Fortunately, there is a mechanism for handling this situation (forward-referencing within a single file).  Run f2c once with the -P option; this will generate a prototype file.  Then run it again, naming both foo.f and foo.P on the command line.  You'll find that it corre









ctly types H as a doublereal function.

	% f2c -P foo.f
	  .
	  .
	Rerunning "f2c -P ... foo.f foo.P" may change prototypes or declarations
	% f2c -P foo.f foo.P
	  .
	  .
	% grep h_ foo.c	
	    extern doublereal h_();
	    qgausx_((E_fp)h_, x1, x2, ss);
	doublereal h_(real *xx)
	} /* h_ */

	% man f2c
		   ..............................................  File
	     names that end with `.p' or `.P' are taken to be prototype
	     files, as produced by option `-P', and are read first.
		   ...............................................

Looks like you have found a little idiosyncracy of Fortran.  Always read the man page before using software.
-- 
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Mark Maimone				phone: (412) 268 - 7698
Carnegie Mellon Computer Science	email: mwm@cs.cmu.edu
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