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From: cik@l.cc.purdue.edu (Herman Rubin)
Newsgroups: comp.lang.fortran
Subject: Re: Calling a C function from Fortran.
Summary: This is how the horror happened
Message-ID: <2425@l.cc.purdue.edu>
Date: 3 Aug 90 02:13:33 GMT
References: <1990Aug2.191231.11783@portia.Stanford.EDU>
Organization: Purdue University Statistics Department
Lines: 22

In article <1990Aug2.191231.11783@portia.Stanford.EDU>, volovich@dendrite.Stanford.EDU (Gene Volovich) writes:
> I'm calling a C function from a FORTRAN program on an RT running AOS, and 
> using the standard C compiler and f77.  I actually got this to run, but 
> my question is this: why does there need to be an underscore after the name
> of the C function I'm calling?  Here's my code:

			[Code deleted]

I do not know when this was introduced, but unlike the older systems I have
used, in many a name is not a name.

In all the Unix systems I have seen, if a Fortran program uses xyz for a name
of a variable, function, subroutine, array, etc., it gets translated into 
_xyz_.  Similarly, the C name abc becomes _abc.  Thus if Fortran calls the
function pdq, the C function would have to be (in C) pdq_.   Also, Fortran
calls by reference, and C calls by value.  So if Fortran has the argument
x, it really passes the address of x, and C must use *x to get the value.
This is more understandable.
-- 
Herman Rubin, Dept. of Statistics, Purdue Univ., West Lafayette IN47907
Phone: (317)494-6054
hrubin@l.cc.purdue.edu (Internet, bitnet)	{purdue,pur-ee}!l.cc!cik(UUCP)