Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!ncar!boulder!hartzell
From: hartzell@boulder.colorado.edu (George Hartzell)
Newsgroups: comp.sys.mips
Subject: mips cc "shortcoming" with compile time array initializtion.
Message-ID: <21901@boulder.Colorado.EDU>
Date: 5 Jun 90 18:33:22 GMT
Sender: news@boulder.Colorado.EDU
Reply-To: hartzell@beagle (George Hartzell)
Organization: University of Colorado, Boulder
Lines: 46


The following test program compiles and runs on suns (SUNos 4.0x,
sun4), but will not compile on a MIPS with the 2.0 compilers or a
DECstation with the 1.31 compiler suite.  There error message is (this
is from the DECstation)
   ccom: Error: moose.c, line 8: constant expected
         static int ia[] = {  ((char *) &X.a - (char *) &X),  ((char *)
   X.b - (cha
   r *) &X),  ((char *) &X.c - (char *) &X) } ;
         --------------------------------------------------^
   ccom: Error: moose.c, line 8: illegal initialization
         static int ia[] = {  ((char *) &X.a - (char *) &X),  ((char *)
   X.b - (cha
   r *) &X),  ((char *) &X.c - (char *) &X) } ;
         --------------------------------------------------^

This also works on gcc for the DECstation...

I have two questions:
    a) should this be legal [in the ansi sense?, in the practical
       sense?] (The compiler should have all the info it needs to
       figure this out, shouldn't it?) 
    b) do the 2.10 compilers support this construction?

g.

-----cut here for sample program --------------------------------------------
#define CharAttI(a) ((char *)  X.a - (char *) &X)
#define AttIndex(a) ((char *) &X.a - (char *) &X)

typedef struct { int a; char b[8]; int c; } Thing;

static Thing X;

static int ia[] = { AttIndex(a), CharAttI(b), AttIndex(c) } ;

main()
{

printf( "\nia: %d %d %d\n", ia[0], ia[1], ia[2] ) ;

}

George Hartzell			                  (303) 492-4535
 MCD Biology, University of Colorado-Boulder, Boulder, CO 80309
hartzell@Boulder.Colorado.EDU           ..!ncar!boulder!hartzell