travis@mojo.columbia.edu (Travis Lee Winfrey) (08/30/88)
In article <8808240932.AA08805@prep.ai.mit.edu> gordon%stats.ucl.ac.uk@NSS.CS.UCL.AC.UK writes: >Should it be possible to include C++ statements in a >yacc file, "compile" with yacc (or better bison?) and compile the >result with g++? Yes, it *should* be possible. I've been doing that all summer with Yacc/CC. I haven't used bison/g++, only because of the bugs and general flakiness of g++. (spare me the flames, I'm sure it will become a fine compiler.) The action statements in yacc are only translated, with $$, $1, etc., being rewritten appropriately. Getting the typing right can be a mild problem. Generally, it works exactly as you would expect it to. The biggest problems I had were with CC, not with g++, and they both involved static initializers: 1) when I used the default main() in liby.a, main() wasn't compiled by CC, so _main() wasn't called from main(), so any static initializers of variables were *not* called. This causes subtle bugs in your programs if you don't use streams IO, and immediate core dumps if you do. 2) peripherally related to YACC, I had problems with an initial yylex() which used cin, didn't use cout, and dumped core immediately on trying to read a character. This is easy to repeat, as #include <stream.h> main() { char ch; cin >> ch ; } dumps core with our streams library. If any reference to cout is made, even if it can never be called (e.g., "if ( x && ! x ) cout.put(x);"), then the program doesn't dump core. CC always failed, but g++ handled it correctly. I tracked this down to the tied_to field of the cin structure, which contains the address of cout. cout wasn't initialized because it was never called. I didn't follow the bug into the cout routines, because I could patch it here: since tied_to was not called if it was null, the fix was just to add "(void) cin.tie(0);" to the program. This bug has probably been fixed in later versions of streams, but it's a pretty special case. t Arpa: travis@mojo.cs.columbia.edu Bitnet: travis@cu20b Usenet: rutgers!columbia!travis Dragnet: "just the facts, ma'am" USMail: 483 Mudd, Columbia Univ., NYC 10025 Phone: 212-280-8091