以下包装类是否是使用std::unique_ptr保留中间对象以访问me成员而不复制me的“可行”方式?
以下是示例:
#include <iostream>
#include <memory>
/* myobj from another library */
class myobj {
public:
std::string me; /* actual member of interest is larger and more
complicated. Don't want to copy of me or myobj */
/* more members in actual class */
myobj(std::string i_am) {
/* more stuff happens in constructor */
me = i_am;
}
~myobj(){
std::cout << me << ": Goodbye" << std::endl;
}
};
/* A function in another library */
void who_is_this(std::string *who){
std::cout << "This is " << *who << std::endl;
}
/* wrapper which I define */
class myobj_wrapper {
using obj_ptr = std::unique_ptr<myobj>;
obj_ptr ptr;
public:
std::string *who;
myobj_wrapper(std::string i_am):
ptr(new myobj(i_am)), who(&ptr.get()->me) {}
myobj_wrapper(myobj &the_obj): who(&the_obj.me) { }
};
int main()
{
{
myobj bob("Bob");
who_is_this(myobj_wrapper(bob).who);
}
who_is_this(myobj_wrapper("Alice").who);
return 0;
}
生成的程序产生以下结果:
This is Bob
Bob: Goodbye
This is Alice
Alice: Goodbye
我定义了myobj_wrapper
,用于获取多个对象的who
指针。我不确定感兴趣的对象(在上面是std::string
)是否会在who_is_this
函数中被评估之前被销毁。从上面看来好像不会,但我应该预料到这种情况吗?上述解决方案有什么缺陷吗?
who_is_this(myobj_wrapper("Alice").who);
中动态分配的对象。 - Benjamin Christoffersen