string_inside_union.cpp

#include <string>


struct A
{

    // You need to explicitly define constructor and destructor
    
    union
    {   
        std::string a;
        int b;
    };
    int state;
    
    A(std::string x)
        : a(std::move(x))
        , state(1)
    {  }
    
    A(int x)
        : b(x)
        , state(0)
    {  }
    
    ~A()   
    {
        if (state) a.std::string::~string(); // Manually call destructor of std::string
    }

};

int main()
{   
    A a(1);
    A b("hello world");
}

clang++编译错误
string_inside_union.cpp:30:16: error: expected unqualified-id
if (state) a.(std::string::~string)(); // Manually call destructor of std::string