Cannot push_back/create object with mutex member on to vector due to copy deleted

Question

I have a std::vector<S>, where struct S contains many data members, including a mutex. Some of these members are initialized by the constructor.

I have created a self-contained example below, where I create and add to the vector once the constructor values are available:

#include <vector>
#include <mutex>

struct S
{
    S() = default;

    S(int a, double b, char c) : a_(a), b_(b), c_(c){}

    std::mutex mutex_;
    int a_;
    double b_;
    char c_;
    // + Many more class members
};

int main()
{
    std::vector<S> vec;

    // Later when constructor arguments are known
    vec.push_back(S(6, 6.7, 'f'));
}

However, because one of the members is a std::mutex I cannot perform the assignment:

<source>:19:16: note: copy assignment operator of 'S' is implicitly deleted because field 'mutex_' has a deleted copy assignment operator

I understand the basics why this error exists- you can't copy a mutex.

I'd prefer not having to write a copy constructor because I have a lot of class members and it seems overkill just to allow mutex to be copyable.

Are there any alternative solutions?

@Dmitry that [would not fix this error](https://godbolt.org/z/zTW7GPEaf). — Drew Dormann, Aug 02 '23 at 18:09
You will need to explicitly make your type movable. Because std::mutex is neither movable nor copyable, this is a bit tricky. You can look at https://stackoverflow.com/questions/29986208/how-should-i-deal-with-mutexes-in-movable-types-in-c for guidance. — Dean Johnson, Aug 02 '23 at 18:29
@rare77 do you need the vector to be resized later or do you just need a dynamically sized (but not resizable) array? — Jan Schultke, Aug 03 '23 at 01:23

Cannot push_back/create object with mutex member on to vector due to copy deleted

0 Answers0