How do I initialize vector/array using an enum?

Question

I am wondering if there are some way to initialize a vector using an enum. The enum is necessary because I am creating a vector of objects (same class, Chess_piece, but different type). I want to be able to access the element without a lot of tests (if (this is white pawn 8)...). The enum can be used to itemize the pieces in a nice way vec(W_PAWN8).... Anyway when I create vector I do something like this (pseudo code)

//generate enum of pieces
enum pieceList{
...
} pieceEnum;
vector<int> pieceIter = {W_PAWN1,W_PAWN2,...}; //equal to {1,2,...}
//board index goes from lower left to upper right
vector<int> boardIdx = {8,9,10,11,12,13,14,15,16,1...};
vector<Piece*> pieceVec;
for (int i=0; i<32; i++)
    pieceVec.pushback( new Piece( boardIdx(i), pieceIter(i) ) );

However, now I actually write the same thing 2 times. Both when I create the enum and pieceIter. For this program I can live with it, but I may have the same issue more than once.

This is why I wonder, does it exist something like vector<int> pieceIter {pieceEnum}; in c++? The code snippet in the previous sentence is invalid of course, but I think it hints my problem, to use all variables in the enum and initialize the vector in a simple way?

If not, is it possible to use some kind of "range initialization" for vector like in matlabl Something like:

vector<int> vec {1:32};

But with c++ syntax?

std::iota = 1 possibility. that said, when you lack tool, create it. — Cheers and hth. - Alf
– Cheers and hth. - Alf, Commented Dec 17, 2014 at 18:17
@Cheersandhth.-Alf That is of course a possibility, I did not know about std::iota. Thanks! I guess that the other way, initializing a vector/array with an enum may require some more work. And possibly support from the compiler. — patrik
– patrik, Commented Dec 17, 2014 at 18:34
@patrik This isn't an attempt to answer the question, but this would make more sense to me as a std::map<pieceList, Piece> and have the boardIdx be a member of the Piece. — Jonathan Mee
– Jonathan Mee, Commented Dec 17, 2014 at 18:49
@patrik Welp, I did this to you. Sorry StackOverflow is so hateful of late. Another note on the context here though: I assume your std::map's value is actual Pieces? Cause it doesn't really make sense to use a map to an index for a std::vector. — Jonathan Mee
– Jonathan Mee, Commented Dec 17, 2014 at 20:28

Henri Hyyryläinen · Accepted Answer · 2014-12-18 17:02:48Z

4

One way to solve this would be adding a value to the enum that is always the last one. Then you could fill the vector by looping up to the value. Something like this:

enum VALUES{

    VALUES_FIRST = 0,

    VALUES_SECOND,

    VALUES_END
};

std::vector<VALUES> Allvalues;

for(int i = 0; i < VALUES_END; i++){
    Allvalues.push_back(static_cast<VALUES>(i));
}

Would fill the vector with all the values in the enum (not including the last marker value) as long as you don't put anything after VALUES_END.

edited Dec 18, 2014 at 17:02

answered Dec 17, 2014 at 18:40

Henri Hyyryläinen

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2 Comments

patrik Over a year ago

I see, that would work for a enum increasing with steps of 1, starting at 0 at least. However, I guess that you mean i <= VALUES_LAST or i<VALUES_LAST+1. I can accept that and i you also have a solution for a general enum, where the values doe not need to increase with steps of 1 I would appreciate it.

Henri Hyyryläinen Over a year ago

As far as I know C++ doesn't store the enum values so that you could retrieve them at runtime making it impossible to iterate over the enum values.

Gabriel · Accepted Answer · 2014-12-17 18:46:33Z

3

So if you want to generate a range from 1 to 32 you can use generate to do that, combined with a lambda.

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int main() {
    vector<int> v(32);
    int n=0;
    std::generate(v.begin(), v.end(), [&]{ return ++n; }); 

    //to display the results
    for (auto& it: v){
        cout<<it<<" ";
    }
    return 0;
}

Output: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

Hope that helps

answered Dec 17, 2014 at 18:46

Gabriel

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1 Comment

patrik Over a year ago

Nice! I guess that I will make a function that does this.

A-Sharabiani · Accepted Answer · 2021-02-01 01:24:53Z

0

You can also use the vectors constructor to initialize the vector like follows:

enum MyEnum {
  FIRST,
  SECOND,
  THIRD
};

// Example 1:
vector<int> v1(4, MyEnum::FIRST); // init a vector of size 4 to "FIRST".

// Example 2:
vector<MyEnum> v2(4, MyEnum::SECOND); // int a vector of enums.

// Example 3
vector<int> v3 {MyEnum::FIRST, MyEnum::THIRD}; // vector of int of size 2 with different values.

// Example 4:
vector<MyEnum> v4 {MyEnum::FIRST, MyEnum::THIRD}; // vector of enum.

answered Feb 1, 2021 at 1:24

A-Sharabiani

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