相关疑难解决方法(0)

假设我有这个功能:

void my_test()
{
    A a1 = A_factory_func();
    A a2(A_factory_func());

    double b1 = 0.5;
    double b2(0.5);

    A c1;
    A c2 = A();
    A c3(A());
}

在每个分组中,这些陈述是否相同？或者在某些初始化中是否有额外的(可能是可优化的)副本？

我见过有人说过这两件事.请引用文字作为证据.还请添加其他案例.

请考虑以下代码:

class A {
private:
  std::string s;
public:
  A() = delete;
  A(const A&) = delete;
  A(A&&) = delete;
  A(const std::string &a) : s(a) {}
};

现在,我想初始化一个使用列表初始化的A数组.g ++(4.9.1)可以成功构建以下代码:

int main() {
  A arr[2] = {{"a"}, {"b"}};
  return 0;
}

但是,它失败了以下代码:

class Aggr {
private:
  A arr[2];
public:
  Aggr() : arr{{"a"}, {"b"}} {}
};

错误消息是,

test.cc: In constructor ‘Aggr::Aggr()’:
test.cc:22:28: error: use of deleted function ‘A::A(A&&)’
   Aggr() : arr{{"a"}, {"b"}} {}
                            ^          
test.cc:11:3: note: declared here
   A(A&&) = delete;
   ^

也就是说,list-initializer尝试调用move构造函数来初始化类中的数组.但是,该代码是由clang v3.5成功构建的,没有任何警告.所以,我想知道C++ …

我有一个名为'Container'的类,其中必须存储三个(在编译时已知)DontCopyMe类的对象.DontCopyMe类具有非默认构造函数和已删除的复制构造函数.如何初始化Containter？

示例代码:

#include <string>

class DontCopyMe
{
    public:
        DontCopyMe(const unsigned int SomeInt, const std::string & SomeString): SomeInt(SomeInt), SomeString(SomeString)
        {
        }
        DontCopyMe(const DontCopyMe &) = delete;
        DontCopyMe & operator = (const DontCopyMe &) = delete;
        DontCopyMe(DontCopyMe &&) = delete;
        DontCopyMe & operator = (DontCopyMe &&) = delete;

    private:
        const unsigned int SomeInt;
        const std::string SomeString;
};

class Container
{
    public:
        Container(): Array{{1, "A"}, {2, "B"}, {3, "C"}}
        {

        }

    private:
        DontCopyMe Array[3];
};

int main()
{
    Container C;
    return 0;
} …