Xref: utzoo comp.lang.c:17143 comp.unix.xenix:5425
Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!lll-winken!uunet!melpar!toppin
From: toppin@melpar.UUCP (Doug Toppin)
Newsgroups: comp.lang.c,comp.unix.xenix
Subject: cc treats third level of struct differently?
Keywords: cc bit-fields structs
Message-ID: <193@melpar.UUCP>
Date: 23 Mar 89 23:52:59 GMT
Distribution: usa
Organization: E-Systems, Falls Church, VA
Lines: 67

We have a problem with a far pointer to a variable that has
three levels of structures in it with the innermost defining
a bit field. It works fine with fewer levels. I did not think
that the level of embedded struct caused a different compiler
action. Does anyone know what is wrong? I can find no reference
to anything like this in my manuals.
The smallest source that duplicates the problem follows.
thanks
Doug Toppin
uunet!melpar!toppin

/*
Are three or more levels of structure depth combined with bit field
definitions implied to be resolved with near pointers?
We are running IBM Xenix 2 on a 286 and are having a problem that
appears as if the compiler forces near pointers as deeper
embedded structures are found.

This creates three types, each contained within the next,
it then defines a pointer to the type. The innermost
structure has one variable that is 8-bits wide.
Memory is allocated using 'brkctl' (which returns a far (32-bit)
pointer). The 'brkctl' has nothing to do with the problem. It is
only included for completeness.
This is compiled with:

cc -Me brkctl.c -o brkctl

When this compiles the following error is returned:

brkctl.c(54) : warning 60: conversion of a long address to a short address

The error is the assignment line:
    tmp->level2.level3.a = 1;

This error is generated by the compiler only if there is a bit
field definition in the third or greater depth level.
*/

#include <stdio.h>
#include <sys/brk.h>

typedef struct
{
    struct
    {
        struct
        {
            unsigned int a : 8;    /* note bit field definition */
        } level3;
    } level2;
} DATA;

DATA far *tmp;
DATA far *brkctl();

main()
{
    tmp = brkctl(BR_NEWSEG, 64000L, (char *) 0); /* allocate memory */
    if (tmp == (DATA far *) -1)
    {
        fprintf(stderr, "Memory not available\n");
        exit(1);
    }
    tmp->level2.level3.a = 1;

} /* main */