C++ MuParser parsing not behaving as expected

Question

I've just started playing with MuParser - seems like a really cool library! However, I'm stuck on parsing the following expression. Can anyone see from the code snippet below where I'm going wrong? Whatever 'count' is the result always seems to be 0??

mu::Parser parser;

string rule = "(n%10==1&&n%100!=11?0:n%10>=2&&n%10<=4&&(n%100<10||n%100>=20)?1:2)";
parser.DefineConst("n", count);
parser.SetExpr(rule);
int retVal = parser.Eval();

Thanks!

Indeed, the expression seems unsatisfiable, isn't it? – A.S.H Dec 24 '16 at 05:06 — A.S.H, Dec 24 '16 at 05:06

score 1 · Answer 1 · answered Dec 25 '16 at 00:33

1

For anyone interested. I added a modulo operator by adding the following:

parser.DefineOprtChars("%");
parser.DefineOprt("%", moduloOperator, mu::prINFIX);

double moduloOperator(double v, double w) {
        return (int)v % MAX(1, (int)w);
};

answered Dec 25 '16 at 00:33

user7227230

59
1
9

Yes. I run your code and my error was undefined symbol "%" . – saeid zamani Dec 25 '16 at 08:07

score 0 · Accepted Answer · answered Dec 24 '16 at 10:06

0

so, i think your code is wrong. it fall at run time. you can put your code in try{}catch{} to find your problem. for example :

        try
{
    mu::Parser parser;
    string rule = "(n%10==1&&n%100!=11?0:n%10>=2&&n%10<=4&&(n%100<10||n%100>=20)?1:2)";
    parser.DefineConst("n", count);
    parser.SetExpr(rule);
    int retVal = parser.Eval();

    std::cout << retVal << std::endl;

}
catch (Parser::exception_type &e)
{
    std::cout << e.GetMsg() << std::endl;
}

answered Dec 24 '16 at 10:06

saeid zamani

71
8

That's strange. The block of code I posted is actually wrapped with a try / catch. It wasn't throwing for me but you say it does for you? Also I evaluated the expression in the debugger at runtime swapping out n for 0 and got 2 as the result which is what I'd expect. I'll double check... – user7227230 Dec 24 '16 at 14:10
Okay. That's crazy. So I've re-run and I am now getting it to throw an exception as you say at position 2 so it looks like it doesn't like the mod '%' symbol. Is there some setup required for mods? – user7227230 Dec 24 '16 at 21:31
Ah. It looks like the mod operator isn't supported - https://github.com/beltoforion/muparser/issues/20 That's a shame. I wonder if there's an easy way to add/extend for this? – user7227230 Dec 24 '16 at 21:35

C++ MuParser parsing not behaving as expected

2 Answers2