Question

Hey guys I have a problem with my program, I am trying to read in a grammar putting multiple right hand rules to a left hand rule using multimapping. The thing is that let’s say the rule is:
a -> al be ze
it maps [a, al] and ignores the rest.
Leaving the key alone, I want to put different attributes to that key.
Was wondering if you guys could spot an error that I cannot seem to find.
Am I using multi-mapping incorrectly?
Thank you.

map<string, string> rule;   // global var  
void righthandside(){       // get rhs of grammar rule

        char c;
    skipSpace();
    c = getchar();
    if(isalpha(c)){
        checkforE = false;  // rule not epsilon
        while(isalnum(c)){
            righths += c;
            c = getchar();
        }
        righths += '\0';
        rule.insert(pair<string, string>(LHS[lhs], righths)); 
        righths.clear();
        righthandside();
    }
    else if(c == '#'){
        if(checkforE == true)
            rule.insert(pair<string, string>(LHS[lhs], epsilon));  // rule states NT goes to epsilon
        skipSpace();
        c = getchar();

        if(c == '#'){           //end of file
                cout << "end of file \n";
        }

        else{                   // end of rule 
            ungetc(c, stdin);
            lhs++;
            readGR();
        }
    }
    else{ 
        errorcode(0); 
    }
}

Answer 1

If you want a single unique key with multiple values you could use std::map with a container for the values such as:

std::map<std::string, std::vector<std::string> > rule;

If you want duplicate keys with one value each you could instead use std::multimap like this:

std::multimap<std::string, std::string> rule;

That would allow rule to contain the pairs [a,al], [a,be], [a,ze]