CODEWITHSUNDEEP
c++compiler-constructionbisondynamic-arraysbisonc++
Justin Smith
Justin Smith

Reputation: 17

How do I manipulate this dynamic vector for fold operations

I am working with flex/bison to create an interpreter for a class. The problem that I am encountering seems to be related to using/converting a dynamic vector. I am trying to create a function to evaluate fold operations, but I hit a roadblock. The list type is specified as a dynamic vector to allow for any number of arguments to be passed to it.

%union {
    CharPtr iden;
    Operators oper;
    double value;
    vector<double>* list;
}

%type <list> list expressions list_choice

The bison direction is to pass the direction of the fold, the operator for the fold, and the dynamic vector to the function evaulateFold().

FOLD direction operator list_choice ENDFOLD SEMICOLON {$$ = evaluateFold($2, $3, $4);}

Once I get it to this point, I cannot do anything with the dynamic array. I tried to copy it to a regular array using for loops but it says that there is no start point reference for the dynamic array this range-based 'for' statement requires a suitable "begin" function and none was foundC/C++(2291). I tried passing the array to evaluateFold() using ,const std::vector<double>& values, but then it says that there is no way to convert std::vector<double>* to std::vector<double>&``no suitable constructor exists to convert from "std::vector<double, std::allocator<double>> *" to "std::vector<double, std::allocator<double>> &"C/C++(415). How am I supposed to be able to use this array for the function?

double evaluateFold(Operators direction, Operators action, vector<double>* values){

    double result = 0;
    switch(direction){
        case LFOLD:
            switch(action){
                case SUBTRACT:
                    subFromLeft(values);
                    for (auto i : values)
                        cout << i << endl;
                    break;
            }
        case RFOLD:
            switch(action){
                case SUBTRACT:
                    for (auto i : values)
                        cout << i << endl;
                    break;
            }
            break;
    }
    return result;
}

I was trying to use a variadic function for the actual fold function, but I cannot even get the vector to allow me to use it.

template <typename ...Args>
auto subFromLeft(Args ...args)
{
    return (... - args);
}

I did just pass the dynamic array all the way using vector<double>* values, but then it said there was no way to resolve vector<double>* values to a double, which would be the result I need from the operation.

Here is another way I tried to complete the fold operation but again, it would not let me use the const std::vector<double>& values reference because it said there is no viable conversion.

double subFromLeft(const std::vector<double>& values) {
    if (values.empty()) return 0;  // Handle empty vector
    double result = values[0];

    for (size_t i = 1; i < values.size(); i++) {
        result -= values[i];
    }

    return result;
}

If anybody could help me resolve this, or at least point me in the right direction, that would be awesome. It is more a question of C++ than flex/bison, but maybe there is some trick in flex/bison that I am not aware of that will help me.

Make generates this:

parser.y: In function ‘int yyparse()’: parser.y:127:146: error: invalid initialization of reference of type ‘std::vector<double>&’ from expression of type ‘std::vector<double>*’

In file included from parser.y:21: values.h:18:76: note: in passing argument 3 of ‘double evaluateFold(Operators, Operators, std::vector<double>&)’

Below is a sample of what the fold function would interpret/evaluate.

// Test Left Fold

function main returns integer;
begin
    fold left - (3, 2, 1) endfold;
end;

Upvotes: -1

Views: 65

Answers (1)

Justin Smith
Justin Smith

Reputation: 17

@Yksisarvinen originally commented it but he erased the comment for some reason. Using (*values) to dereference the dynamic array vector<double>* values allowed me to send it to the other function easily and get the result. A couple of others answered but @Yksisarvinen was the first to mention it.

Upvotes: 0

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