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From: tomm@voodoo.UUCP (Tom Mackey)
Newsgroups: comp.lang.c
Subject: current prototypes
Message-ID: <393@voodoo.UUCP>
Date: Tue, 11-Aug-87 17:32:39 EDT
Article-I.D.: voodoo.393
Posted: Tue Aug 11 17:32:39 1987
Date-Received: Sat, 15-Aug-87 08:33:54 EDT
Reply-To: tomm@voodoo.UUCP (Tom Mackey)
Distribution: world
Organization: Voodoo Graphics Project
Lines: 92
Keywords: VMS, C, C prtotypes


NOTICE: I am posting this for a friend of mine whose news software
is a bit brain damaged.  Please respond to him, or follow this up,
but do not reply or respond to me.  The path I use to get to John
Campbell, the author of this article, is:

Path to naucse:  ssc-vax!uw-beaver!rutgers!hao!noao!arizona!naucse!jdc

Thanks...his article follows.

------------------cut here------------------------
Path: naucse!jdc
From: jdc@naucse.UUCP (John Campbell)
Newsgroups: comp.lang.c
Subject: current prototypes
Keywords: VMS 'C', 'C' prototypes
Message-ID: <372@naucse.UUCP>
Date: 3 Aug 87 03:33:26 GMT
Organization: Northern Arizona University, Flagstaff, Arizona
Lines: 58


>From the VMS Guide to VAX C manual (VMS 'C' version 2.3-024):

    If the data type of an argument in a function call does not match
    the prototype, VAX C attempts to perform conversions.  If the
    mismatched argument is assignment compatible with the prototype
    parameter, VAX C converts the argument to the data type specified
    in the prototype, according to the parameter and argument conversion
    rules (...).

    If the mismatched argument is not assignment compatible with the
    prototype parameter, the action generates the appropriate error
    message and the results are undefined.

Here is a listing (with /MACHINE interspersed) of a program that compiles
without any complaints:

    1
    2           void farm_it (int aa, char **bb);
    3           main()
    4           {
                        main:
                                .entry  main,^m<r2,r3>
                                subl2   #4,sp
                                jsb     C$MAIN

    5    1         int a;
    6    1         float b;
    7    1
    8    1         farm_it (a, b);
                                cvtfl   r2,-(sp)
                                pushl   r3
                                calls   #2,FARM_IT

    9    1      }
                                movl    #1,r0
                                ret

   10
   11           void farm_it (a, b)
   12           int a;
                        farm_it:
                                .entry  farm_it,^m<>
                                subl2   #4,sp

   13           float b;
   14           {
   15    1         b = a;
                                cvtld   4(ap),8(ap)

   16    1      }
                                ret


Changing the definition of farm_it to use the new style function
definition with this compiler (eg void farm_it (int a, float b) {})
will cause the compiler to give an error message about mismatched
arguments.

Questions: 
Should old and new style definitions yield different behaviors?
Is this the expected way to implement prototypes?  
Are prototypes all that useful in such an implementation?
Is it really correct to CVTFL in the guise of "assignment compatibility"?
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-- 
Tom Mackey                                (206) 656-7724 (wk)
Boeing Computer Services    ....uw-beaver!ssc-vax!voodoo!tomm
M/S 6M-17,     P.O. Box 24346,     Seattle, WA     98124-0346