How to resize a global std::vector of std::mutex once it's been defined?

Asked Mar 08 '23 at 10:28

Active Mar 08 '23 at 10:28

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I am trying to use a vector of mutexes, but want to resize them after they are defined. However, I am getting a compilation error

error: static_assert failed due to requirement 'is_constructible<std::mutex, std::mutex &&>::value' "result type must be constructible from value type of input range" static_assert(is_constructible<_ValueType2, decltype(__first)>::value,*

Here is the code in godbolt

#include <iostream>
#include <vector>
#include <mutex>

std::vector<std::mutex> g_v(4);

int main() { 
    g_v.resize(2);
    std::cout<<"v.size() =  " << g_v.size()<<'\n';
}

https://godbolt.org/z/K85MEPM8E

Could someone explain the meaning of such an error message and how to solve the issue?

asked Mar 08 '23 at 10:28

dochoex

3

`std::mutex` can't be copied or moved. – molbdnilo Mar 08 '23 at 10:34
3

I guess the real question is why you want to resize a vector of mutexes. – john Mar 08 '23 at 10:35
1

resize might require to reallocate and that wont work with `std::mutex`, wether it actually has to reallocate is only known at runtime, thats why it fails even if you do not reallocate – 463035818_is_not_an_ai Mar 08 '23 at 10:36
1

fwiw you can `pop_back`. https://godbolt.org/z/4dKhenMqr. – 463035818_is_not_an_ai Mar 08 '23 at 10:39
Thank you all, @463035818_is_not_a_number pop_back is a good option, tested your change in godbolt. The reason is to keep size limited to the actual need and do that once. – dochoex Mar 08 '23 at 11:31

How to resize a global std::vector of std::mutex once it's been defined?

0 Answers0