如何在交换机的情况下使用右值引用

由 发布于 c++switch-statementrvalue-reference
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I want to use t(rvalue reference) in a case of switch(T), but I get an error the value of 't' is not usable in a constant expression. How to do it the right way.

#include <iostream>
using namespace std;
int main(){
    int (&&t)=5;
    int T{};
    switch(T){
        case t:   // error in this case
            cout<<t<<endl;
            break;
        default:
            cout<<"default"<<endl;
            break;
    }
}
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思雁
思雁

You can't use an rvalue reference as a case label, since it is not a constant expression. You can however use a const int variable:

int const t = 5;
switch(...)
{
  case t : ...  // ok
}

这可能应该是：

constexpr int t = 5;

也一样

请注意，尝试执行以下操作：

int const &&t = 5;

will not work either, since the initializer is not a constant expression, so there is no way that I'm aware of that lets you use an rvalue reference as a case label.

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