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From: bobg+@andrew.cmu.edu (Robert Steven Glickstein)
Newsgroups: comp.lang.c
Subject: Varargs problem
Message-ID: <4YxPuc200VsnE_B3Jy@andrew.cmu.edu>
Date: 25 Aug 89 21:48:24 GMT
Organization: Information Technology Center, Carnegie Mellon, Pittsburgh, PA
Lines: 46


I wish to extract a variable of type "pointer to function returning int"
[(int (*) ())] from a varargs parameter list, and I can't.  My function
looks like the usual:

    foo(va_alist) va_dcl
    {
        va_list ap;
        int (*fn)();

        va_start(ap);
        fn = va_arg(ap, int (*) ());
        va_end(ap);
    }

The problem, at least in my OS's implementation, is that the va_arg
macro is defined as

    # define va_arg(list,mode) \
        ((mode *)((list += (sizeof(mode)+3)&(-4))\
        -((sizeof(mode)<4)?sizeof(mode):\
        (sizeof(mode)+3)&(-4))))[0]

and a typecast operator like (int (*) ()) is turned into (int (*) () *)
by the macro, on which the compiler barfs.

I might be able to do

    fn = (int (*) ()) va_arg(ap, char *);

but I don't know how portable this is, and I'd like to do this in a
highly portable fashion.  Any suggestions?

_______________________________
Bob Glickstein, System Designer
Information Technology Center  room 220
Carnegie Mellon University
Pittsburgh, PA  15213-3890
(412) 268-6743

Internet: bobg+@andrew.cmu.edu
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