CODEWITHSUNDEEP
c++c++17
George Austin Bradley
George Austin Bradley

Reputation: 330

How to get the std::fill function to work with a std::map?

I want to use the std::fill function from the algorithm library to fill in '-' in the second part of the pair. Is this possible to achieve?

#include <algorithm>
#include <map>
int main()
{
    std::map<int, unsigned char> board(10);

    // What I want the std::fill to do the equivalent of  
    for (auto& cell : board) {
        cell.second = '-';
    }

    // What I've tried:
    std::fill(board.begin(), board.end(), [&](auto &pair){pair.second = '-';});
}

Upvotes: 0

Views: 372

Answers (1)

ecatmur
ecatmur

Reputation: 157504

fill assigns to each element of the range it is called on, whereas you want to assign to the values of those elements (key-value pairs). From C++20 you can use the ranges::views::values range adaptor:

std::ranges::fill(std::ranges::views::values(board), '-');

If you can't use C++20, your code will work by changing fill to for_each:

std::for_each(board.begin(), board.end(), [&](auto &pair){pair.second = '-';});

Upvotes: 1

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