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From: EDSTROM%UNCAEDU.BITNET@wiscvm.wisc.EDU
Newsgroups: comp.lang.c
Subject: VMS Descriptors
Message-ID: <7960@brl-adm.ARPA>
Date: Mon, 22-Jun-87 21:19:44 EDT
Article-I.D.: brl-adm.7960
Posted: Mon Jun 22 21:19:44 1987
Date-Received: Tue, 23-Jun-87 07:29:42 EDT
Sender: news@brl-adm.ARPA
Lines: 38

Steve Summit in Message-ID: <1142@copper.TEK.COM> writes:

>There are some header files or something that come with VAXC,
>DEC's VMS C compiler, that make handling descriptors a bit
>easier.

This is correct about descriptors being easy to use. His version of the VMS
"hello world" program might look like this:

    #include descrip
    #define IO$_WRITEVBLK 0x30

    main()
    {
       assign_channel (&channel, "sys$output");
       sys$qiow(0, channel, IO$_WRITEVBLK, 0, 0, 0, "Hello, world!\r", 14,
                                0, 0, 0, 0);
    }

    #define STR_DESC(A,B) struct dsc$descriptor_s A = {strlen(B),DSC$K_DTYPE_T,\
     DSC$K_CLASS_S,B}

    assign_channel (chan, dev_name)
    short int *chan;
    char      *dev_name;
    {
       STR_DESC(device, dev_name);
       sys$assign(&device, chan, 0, 0);
    }


The common calling protocol on VMS is one of its best features. I suppose its
unlikely that this could be built into the major languages. (Sigh.) There
seems to be enough trouble defining the ANSI C specifications without trying
to co-ordinate the ANSI boards for each of the other languages. It is nice not
having to translate old or borrowed FORTRAN, BASIC or PASCAL routines to use
in a new C program. Especially if you don't understand the language the original
routine was written in.