pointer to pointers of vector and arrays

Question

I have a map mapping a character to a 2-d array of rules to process that character. Following is the code:

struct CFG //this struct is data structure to contain a context free grammar
{
   vector<char> *V;
   vector<char> *T;
   map<char,vector<vector<rhs>*>*> *prod;
  // char start;
};

int main()
{
map<char,vector<vector<rhs>*>*> *prod;  //rhs is the type of each cell of the 2-d array
CFG cfg1;
cfg1.V= new vector<char>;

//We imput elements into the V array here......//

cfg1.prod= new map<char,vector<vector<rhs>*>*>;

for(int i=0;i<cfg1.V->size();i++)
 {
    vector<vector<rhs>*>* all_prod_of_one_nonter= new vector<vector<rhs>*>;
    *(cfg1.prod)[*(cfg1.V)[i]]=all_prod_of_one_nonter;  //error occurs here//////
 }
}

In the line, I marked as 'error occurs', the following error occurs:

q1.cpp: In function ‘int main()’:
q1.cpp:93:29: error: no match for ‘operator*’ in ‘**(cfg1.CFG::V + ((unsigned int)(((unsigned int)i) * 12u)))’

I use * to dereference the pointer cfg1.V so that I can use subscript notation to access the array cells. How to remove the error?

This is extremely non-idiomatic C++. You should strongly consider not using a pointer to a map of pointers to vectors of pointers to vectors. Basically, just get rid of all the pointers entirely; you'll find the resulting code a lot simpler. — Oliver Charlesworth
– Oliver Charlesworth, Commented Mar 6, 2013 at 18:50
You don't really need any of the pointers, they are all non-functional in your code. Start by removing all the * s and ->s and news. — n. m. could be an AI
– n. m. could be an AI, Commented Mar 6, 2013 at 18:54
@OliCharlesworth...you are correct..But, I am in the process of learning about STL in c++ and trying to get comfortable in using them along with pointers.Hence the labyrinth.. — AvinashK
– AvinashK, Commented Mar 6, 2013 at 19:00

us2012 · Accepted Answer · 2013-03-06 18:58:36Z

1

(*cfg1.prod)[(*cfg1.V)[i]]=all_prod_of_one_nonter;

(Reason: operator[] (array subscripting) binds more tightly than operator* (indirection).)

edited Mar 6, 2013 at 18:58

answered Mar 6, 2013 at 18:51

us2012

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3 Comments

us2012 Over a year ago

Yeah, I'm sure it did, but still, please consider Oli Charlesworth's advice in the comments to your question.

us2012 Over a year ago

On second thought, it shouldn't have worked because the same problem persists within the array subscript. Edited answer to reflect this.

AvinashK Over a year ago

@us2012..inside I had changed the subscript and instead had used at function. So, it worked.

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