CODEWITHSUNDEEP
c++matrixvectorinitializationboolean
Paige
Paige

Reputation: 1

How do I work with <vector<vector<bool>> in C++?

I am wondering how I would initialize a matrix of 0s given that I want to use a <vector<vector> type and if it is possible to change the elements one by one in the boolean matrix the same as you would with an integer matrix (ex: matrix[row][col] = 1)

EDIT:

for example to make an NxN matrix I am trying:

int n = 5;
std::vector<std::vector<bool>> (n, std::vector<bool>(n, false))

this gives me the following error

error: no match for call to ‘(std::vector<std::vector<bool> >) (int&, std::vector<bool>)’

for reference, I get the same error if I do something like this:

int n = 5;
std::vector<bool> row(n, false);
std::vector<std::vector<bool>> (n, row)

Upvotes: 0

Views: 379

Answers (2)

paxdiablo
paxdiablo

Reputation: 881263

Sure you can. A vector of vector of boolean values may not necessarily be the most efficient means for this(a), but it's certainly doable:

#include <iostream>
#include <vector>

using tMatrix = std::vector<std::vector<bool>>;

void dumpMatrix(const std::string &desc, const tMatrix matrix) {
    std::cout << desc << ":\n";
    for (const auto &row: matrix) {
        for (const auto &item: row) {
            std::cout << ' ' << item;
        }
        std::cout << '\n';
    }
}

int main() {
    tMatrix matrix = { {1, 0, 0}, {1, 1, 1}, {0, 1, 0}, {0, 0, 0}};
    //tMatrix matrix(2, std::vector<bool>(3, false));

    dumpMatrix("before", matrix);
    matrix[0][2] = 1;
    dumpMatrix("after", matrix);
}

The output of that program shows that both aspects work, the initialisation nad the ability to change a single item:

before:
 1 0 0 <- note this final bit (row 0, column 2) ...
 1 1 1
 0 1 0
 0 0 0
after:
 1 0 1 <- ... has changed here
 1 1 1
 0 1 0
 0 0 0

As an aside, the reason why your definition of the matrix isn't working is because of the presence of the word row. There's no place for names in that type definition, you just need the types:

tMatrix matrix(5, std::vector<bool>(5, false));

I've added a similar line to my code above, commented out. If you replace the current declaration of matrix with that, you'll see:

before:
 0 0 0
 0 0 0
after:
 0 0 1
 0 0 0

(a) Unless you need to resize the matrix, you may be better off with a std::array or std::bitset.

Upvotes: 1

ShadowRanger
ShadowRanger

Reputation: 155363

Your mistake was trying to name the inner vector passed to the outer vector's constructor:

std::vector<std::vector<bool>> matrix(n, std::vector<bool> row(n, false))
//                            You can't name the temporary ^^^

should just be:

std::vector<std::vector<bool>> matrix(n, std::vector<bool>(n, false))

Upvotes: 0

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