I was trying to find a way to prove what the associativity (left or right) is for the + operation for a simple bison-generated integer calculator (gcc compiled on Linux). The only way I could think of was to force an overflow in one direction but not the other, e.g., Maxint + 1 + (-1). But the program simply wraps (mod) or crosses over to negative and back as necessary without error so left and right give same result. I tried using an intermediate variable declared as a signed int for the result and also gcc flags like ftrapv, fwrapv, and Wall, but nothing changed. Is there something simple I can do in my C-code to make a program crash or give a runtime warning on MAXINT+1 (2147483647+1)? Does bison generate code that suppresses all error output because I defined a yyerror function?
I'm confused, are you trying to get/prevent run-time overflow, or get the compiler to generate error for you if you actually have overflow during your compilation? If the latter, then gcc (v4.7.2) that I use on my Mageia 3 system automatically has
-Woverflow as a compiler warning, and will catch the INT_MAX+1 condition. Likewise it will also catch the INT_MIN-1. Both are compiler warnings.
Note that executing the code created doesn't core dump, but in, as you say, wraps :-(
Thanks everyone. I purposefully wanted to keep the Bison code simple for my undergrad students to see and modify (changing precedence and assoc for the +, -, *, and / integer-only operators in various ways). I realize one solution is to change the semantics (code generated) to get what I wanted (be it parse trees or runtime overflow messages), but I wanted to avoid that. I really just wanted a simply analysis assignment in which my students had to approach the simple calculator as a black box and discover the precedences and associativity rules by careful experimentation with some well thought out arithmetic expressions to compute.
The integer operations together with boundary-wrapping effects makes it difficult to discover the assoc of + and * (impossible if each has its own precedence level from other operators). An overflow RUN TIME warning message would overcome this and I didn't realize that would be so hard to do (I figured it was a simple gcc argument).
So that was my motivation. It was just a toy problem to make students think and reverse engineer the grammar.
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