stt@inmet (11/09/88)
A simple language extension would be: #include_once "classname.h" which could be defined to be roughly equivalent to: #ifndef classname_h #define classname_h #include "classname.h" #endif This would be similar to the "with" clause from Ada and the "import" capability of Modula-2. This would be a useful addition to ANSI C as well, I would think. S. Tucker Taft ...uunet!inmet!stt; stt@inmet.inmet.com Intermetrics, Inc. Cambridge, MA 02138
mjr@vax2.nlm.nih.gov.nlm.nih.gov (Marcus J. Ranum) (11/10/88)
In article <124300001@inmet> stt@inmet writes: > >A simple language extension would be: > >#include_once "classname.h" > I wonder how much code would break is such an extension were added, and the #include_once were made the DEFAULT rather than the exception ? I still think in the long run we'd be better off with a means of 'including' only those definitions that are needed. This would mean that the pre-processor would need to keep a symbol table, and then have some means of snipping just the needed definition out of the header files. I don't *THINK* it would be too hard to write - some kind of index to the things defined in the standard header files, for speed, then possibly some extensions to allow users to specify WHICH definition to use, if there were multiple ones. EG: <stdio.h>NULL != <myfoo.h>NULL It would entail turning the pre-processor into a programming language, which might not be a bad idea, either. Of course, all this is "through the hat". I personally don't know enough about compiler-writing to have an idea of how to write such a thing efficiently, or where the major conceptual flaws lie. --mjr(); "Strange women lying in ponds, distributing swords is no basis for a system of government. Supreme executive power derives from a mandate from the masses, not from some farsical aquatic ceremony."
akwright@watdragon.waterloo.edu (Andrew K. Wright) (11/14/88)
In article <124300001@inmet> stt@inmet writes: > >A simple language extension would be: > >#include_once "classname.h" The Software Development Group of the University of Waterloo uses #pragma idempotent to mark an include file as having idempotent semantics (that is, including it more than once has no effect). using pragma to do this has the advantage that your program will still compile on a C compiler which does not recognize it; the file will then be included twice, which should not hurt, just slow down your compiles. -- Andrew K. Wright akwright@watmath.waterloo.edu CS Dept., University of Waterloo.