C++简单问题搞复杂之构造函数与初始化（模板类）
接上文
能不能不用std::move()让移动构造函数调用成员和基类的移动构造函数？
可以，如果你没有自定义的操作，使用=default;即可，对拷贝构造函数也适用，赋值也是，计划用另外的文章来讲相关的知识；
C++的模板，又是一个偷懒利器，同时跟构造函数一样，也是幻觉制造机
正如我所说，简单和复杂并没有明确的界限，模板的便利有个前提，你对它了如指掌，构造函数也是一样；
有些数据类型，只是某些特定性质存在差异，处理逻辑是一样的，模板就是这个的干活，如：数值的 float 和 double，字符的 char 和 wchar 等；
那又怎么样，不就是多个模板参数吗？
其实也不怎么样，主要是在模板定义内，由于参数可以省略，编译器无法识别是模板，还是类型，还是构造函数，当然新的C++标准可能会解决这个问题；
就好像枚举，如果两个枚举的项的名称相同，就会出现重名错误，而C++11新增的强枚举类型则可以重名；
越扯越长，我们还是说说构造函数吧
那是我对小姐姐，呸呸，对C++最感兴趣的部分
直接把上文的类，全部模板化一遍，分别是：
BaseT.hpp
template
class BaseT {
protected:
// for further test
T *ptr;
public:
BaseT() { printf("BaseT::BaseT(), this=%p\n", this); }
BaseT(const BaseT &rhs) { printf("BaseT::BaseT(const BaseT &rhs), this=%p, &rhs=%p\n", this, &rhs); }
BaseT(BaseT &&rhs) { printf("BaseT::BaseT(BaseT &&rhs), this=%p, &rhs=%p\n", this, &rhs); }
BaseT(T *p) { printf("BaseT::BaseT(T *p), this=%p\n", this); this->ptr = p; }
virtual ~BaseT() { printf("BaseT::~BaseT(), this=%p\n", this); }
BaseT &operator=(const BaseT &rhs)
{
printf("BaseT::operator=(const BaseT &rhs), this=%p, &rhs=%p\n", this, &rhs);
if (&rhs != this) {}
return *this;
}
BaseT &operator=(BaseT &&rhs)
{
printf("BaseT::operator=(const BaseT &&rhs), this=%p, &rhs=%p\n", this, &rhs);
if (&rhs != this) {}
return *this;
}
};
MemberObjectT.hpp
template
class MemberObjectT {
public:
MemberObjectT() { printf("MemberObjectT::MemberObjectT(), this=%p\n", this); }
MemberObjectT(const MemberObjectT &rhs) { printf("MemberObjectT::MemberObjectT(const MemberObjectT &rhs), this=%p\n", this); }
MemberObjectT(MemberObjectT &&rhs) { printf("MemberObjectT::MemberObjectT(MemberObjectT &&rhs), this=%p\n", this); }
virtual ~MemberObjectT() { printf("MemberObjectT::~MemberObjectT(), this=%p\n", this); }
MemberObjectT &operator=(const MemberObjectT &rhs)
{
printf("MemberObjectT::operator=(const MemberObjectT &rhs), this=%p\n", this);
if (&rhs != this) {}
return *this;
}
MemberObjectT &operator=(MemberObjectT &&rhs)
{
printf("MemberObjectT::operator=(const MemberObjectT &&rhs), this=%p\n", this);
if (&rhs != this) {}
return *this;
}
};
ObjectT.hpp
template
class ObjectT : public BaseT {
protected:
MemberObjectT mo;
public:
ObjectT() { printf("ObjectT::ObjectT(), this=%p\n", this); }
ObjectT(const ObjectT &rhs) { printf("ObjectT::ObjectT(const ObjectT &rhs), this=%p\n", this); }
ObjectT(ObjectT &&rhs) { printf("ObjectT::ObjectT(ObjectT &&rhs), this=%p\n", this); }
ObjectT(T *p) { printf("ObjectT::ObjectT(T *p), this=%p\n", this); }
virtual ~ObjectT() { printf("ObjectT::~ObjectT(), this=%p\n", this); }
ObjectT &operator=(const ObjectT &rhs)
{
printf("ObjectT::operator=(const ObjectT &rhs), this=%p\n", this);
if (&rhs != this) {}
return *this;
}
ObjectT &operator=(ObjectT &&rhs)
{
printf("ObjectT::operator=(const ObjectT &&rhs), this=%p\n", this);
if (&rhs != this) {}
return *this;
}
ObjectT operator+(const ObjectT &rhs) const
{
printf("ObjectT::operator+(const ObjectT &rhs), this=%p\n", this);
ObjectT o1;
return o1;
}
};
现在执行：
test_cpp, ObjectT>(); 结果
BaseT::BaseT(), this=000000573E15F168
MemberObjectT::MemberObjectT(), this=000000573E15F178
ObjectT::ObjectT(), this=000000573E15F168
BaseT::BaseT(), this=000000573E15F198
MemberObjectT::MemberObjectT(), this=000000573E15F1A8
ObjectT::ObjectT(const ObjectT &rhs), this=000000573E15F198
BaseT::BaseT(), this=000000573E15F1C8
MemberObjectT::MemberObjectT(), this=000000573E15F1D8
ObjectT::ObjectT(const ObjectT &rhs), this=000000573E15F1C8
ObjectT::operator+(const ObjectT &rhs), this=000000573E15F168
BaseT::BaseT(), this=000000573E15EFF8
MemberObjectT::MemberObjectT(), this=000000573E15F008
ObjectT::ObjectT(), this=000000573E15EFF8
BaseT::BaseT(), this=000000573E15F1F8
MemberObjectT::MemberObjectT(), this=000000573E15F208
ObjectT::ObjectT(ObjectT &&rhs), this=000000573E15F1F8
ObjectT::~ObjectT(), this=000000573E15EFF8
MemberObjectT::~MemberObjectT(), this=000000573E15F008
BaseT::~BaseT(), this=000000573E15EFF8
BaseT::BaseT(), this=00000159706A27B0
MemberObjectT::MemberObjectT(), this=00000159706A27C0
ObjectT::ObjectT(T *p), this=00000159706A27B0
ObjectT::operator=(const ObjectT &rhs), this=000000573E15F198
ObjectT::operator+(const ObjectT &rhs), this=000000573E15F168
BaseT::BaseT(), this=000000573E15EFF8
MemberObjectT::MemberObjectT(), this=000000573E15F008
ObjectT::ObjectT(), this=000000573E15EFF8
BaseT::BaseT(), this=000000573E15F348
MemberObjectT::MemberObjectT(), this=000000573E15F358
ObjectT::ObjectT(ObjectT &&rhs), this=000000573E15F348
ObjectT::~ObjectT(), this=000000573E15EFF8
MemberObjectT::~MemberObjectT(), this=000000573E15F008
BaseT::~BaseT(), this=000000573E15EFF8
ObjectT::operator=(const ObjectT &&rhs), this=000000573E15F1C8
ObjectT::~ObjectT(), this=000000573E15F348
MemberObjectT::~MemberObjectT(), this=000000573E15F358
BaseT::~BaseT(), this=000000573E15F348
ObjectT::~ObjectT(), this=00000159706A27B0
MemberObjectT::~MemberObjectT(), this=00000159706A27C0
BaseT::~BaseT(), this=00000159706A27B0
ObjectT::~ObjectT(), this=000000573E15F1F8
MemberObjectT::~MemberObjectT(), this=000000573E15F208
BaseT::~BaseT(), this=000000573E15F1F8
ObjectT::~ObjectT(), this=000000573E15F1C8
MemberObjectT::~MemberObjectT(), this=000000573E15F1D8
BaseT::~BaseT(), this=000000573E15F1C8
ObjectT::~ObjectT(), this=000000573E15F198
MemberObjectT::~MemberObjectT(), this=000000573E15F1A8
BaseT::~BaseT(), this=000000573E15F198
ObjectT::~ObjectT(), this=000000573E15F168
MemberObjectT::~MemberObjectT(), this=000000573E15F178
BaseT::~BaseT(), this=000000573E15F168
看来没什么可以说的，跟上文的情形一样，只是模板类具体化了而已；
模板类如何显式调用基类的构造函数？
我们把Object2模板化为ObjectT2.hpp
template
class ObjectT2 : public BaseT {
protected:
MemberObjectT mo;
public:
ObjectT2() { printf("ObjectT2::ObjectT2(), this=%p\n", this); }
ObjectT2(const ObjectT2 &rhs) : BaseT(rhs), mo(rhs.mo) { printf("ObjectT2::ObjectT2(const ObjectT2 &rhs), this=%p\n", this); }
ObjectT2(ObjectT2 &&rhs) : BaseT(rhs), mo(rhs.mo) { printf("ObjectT2::ObjectT2(ObjectT2 &&rhs), this=%p\n", this); }
ObjectT2(T *p) : BaseT(p) { printf("ObjectT2::ObjectT2(T *p), this=%p\n", this); }
virtual ~ObjectT2() { printf("ObjectT2::~ObjectT2(), this=%p\n", this); }
ObjectT2 &operator=(const ObjectT2 &rhs)
{
printf("ObjectT2::operator=(const ObjectT2 &rhs), this=%p\n", this);
if (&rhs != this) {}
return *this;
}
ObjectT2 &operator=(ObjectT2 &&rhs)
{
printf("ObjectT2::operator=(const ObjectT2 &&rhs), this=%p\n", this);
if (&rhs != this) {}
return *this;
}
ObjectT2 operator+(const ObjectT2 &rhs) const
{
printf("ObjectT2::operator+(const ObjectT2 &rhs), this=%p\n", this);
ObjectT2 o1;
return o1;
}
};
菩萨保佑，编译通过，现在就看看this指针是不是所期待的那样
执行
test_cpp, ObjectT2>(); 结果
BaseT::BaseT(), this=000000573E15F168
MemberObjectT::MemberObjectT(), this=000000573E15F178
ObjectT2::ObjectT2(), this=000000573E15F168
BaseT::BaseT(const BaseT &rhs), this=000000573E15F198, &rhs=000000573E15F168
MemberObjectT::MemberObjectT(const MemberObjectT &rhs), this=000000573E15F1A8
ObjectT2::ObjectT2(const ObjectT2 &rhs), this=000000573E15F198
BaseT::BaseT(const BaseT &rhs), this=000000573E15F1C8, &rhs=000000573E15F168
MemberObjectT::MemberObjectT(const MemberObjectT &rhs), this=000000573E15F1D8
ObjectT2::ObjectT2(const ObjectT2 &rhs), this=000000573E15F1C8
ObjectT2::operator+(const ObjectT2 &rhs), this=000000573E15F168
BaseT::BaseT(), this=000000573E15EFF8
MemberObjectT::MemberObjectT(), this=000000573E15F008
ObjectT2::ObjectT2(), this=000000573E15EFF8
BaseT::BaseT(const BaseT &rhs), this=000000573E15F1F8, &rhs=000000573E15EFF8
MemberObjectT::MemberObjectT(const MemberObjectT &rhs), this=000000573E15F208
ObjectT2::ObjectT2(ObjectT2 &&rhs), this=000000573E15F1F8
ObjectT2::~ObjectT2(), this=000000573E15EFF8
MemberObjectT::~MemberObjectT(), this=000000573E15F008
BaseT::~BaseT(), this=000000573E15EFF8
BaseT::BaseT(T *p), this=00000159706A2210
MemberObjectT::MemberObjectT(), this=00000159706A2220
ObjectT2::ObjectT2(T *p), this=00000159706A2210
ObjectT2::operator=(const ObjectT2 &rhs), this=000000573E15F198
ObjectT2::operator+(const ObjectT2 &rhs), this=000000573E15F168
BaseT::BaseT(), this=000000573E15EFF8
MemberObjectT::MemberObjectT(), this=000000573E15F008
ObjectT2::ObjectT2(), this=000000573E15EFF8
BaseT::BaseT(const BaseT &rhs), this=000000573E15F348, &rhs=000000573E15EFF8
MemberObjectT::MemberObjectT(const MemberObjectT &rhs), this=000000573E15F358
ObjectT2::ObjectT2(ObjectT2 &&rhs), this=000000573E15F348
ObjectT2::~ObjectT2(), this=000000573E15EFF8
MemberObjectT::~MemberObjectT(), this=000000573E15F008
BaseT::~BaseT(), this=000000573E15EFF8
ObjectT2::operator=(const ObjectT2 &&rhs), this=000000573E15F1C8
ObjectT2::~ObjectT2(), this=000000573E15F348
MemberObjectT::~MemberObjectT(), this=000000573E15F358
BaseT::~BaseT(), this=000000573E15F348
ObjectT2::~ObjectT2(), this=00000159706A2210
MemberObjectT::~MemberObjectT(), this=00000159706A2220
BaseT::~BaseT(), this=00000159706A2210
ObjectT2::~ObjectT2(), this=000000573E15F1F8
MemberObjectT::~MemberObjectT(), this=000000573E15F208
BaseT::~BaseT(), this=000000573E15F1F8
ObjectT2::~ObjectT2(), this=000000573E15F1C8
MemberObjectT::~MemberObjectT(), this=000000573E15F1D8
BaseT::~BaseT(), this=000000573E15F1C8
ObjectT2::~ObjectT2(), this=000000573E15F198
MemberObjectT::~MemberObjectT(), this=000000573E15F1A8
BaseT::~BaseT(), this=000000573E15F198
ObjectT2::~ObjectT2(), this=000000573E15F168
MemberObjectT::~MemberObjectT(), this=000000573E15F178
BaseT::~BaseT(), this=000000573E15F168
逐个检查，直到移动赋值 o3=o1+o2
善哉，所有指针正常：
1.基类和成员，未指定时调用的是默认构造函数（我们通过上文已经知晓）
2.移动构造函数的右值，在函数内是左值（我们通过上文已经知晓）
3.可以使用 template_name<...> 在初始化列表中指定基类的构造函数
那么
让我们用小姐姐，呸呸，用C++再做点更加离（变）奇（态）的事情
用名称空间隔离，然后派生同名类模板：
namespace Demo
{
template
class BaseT {
protected:
// for further test
T *ptr;
public:
BaseT() { printf("BaseT::BaseT(), this=%p\n", this); }
BaseT(const BaseT &rhs) { printf("BaseT::BaseT(const BaseT &rhs), this=%p, &rhs=%p\n", this, &rhs); }
BaseT(BaseT &&rhs) { printf("BaseT::BaseT(BaseT &&rhs), this=%p, &rhs=%p\n", this, &rhs); }
BaseT(T *p) { printf("BaseT::BaseT(T *p), this=%p\n", this); this->ptr = p; }
virtual ~BaseT() { printf("BaseT::~BaseT(), this=%p\n", this); }
BaseT &operator=(const BaseT &rhs)
{
printf("BaseT::operator=(const BaseT &rhs), this=%p, &rhs=%p\n", this, &rhs);
if (&rhs != this) {}
return *this;
}
BaseT &operator=(BaseT &&rhs)
{
printf("BaseT::operator=(const BaseT &&rhs), this=%p, &rhs=%p\n", this, &rhs);
if (&rhs != this) {}
return *this;
}
};
template
class MemberObjectT {
public:
MemberObjectT() { printf("MemberObjectT::MemberObjectT(), this=%p\n", this); }
MemberObjectT(const MemberObjectT &rhs) { printf("MemberObjectT::MemberObjectT(const MemberObjectT &rhs), this=%p\n", this); }
MemberObjectT(MemberObjectT &&rhs) { printf("MemberObjectT::MemberObjectT(MemberObjectT &&rhs), this=%p\n", this); }
virtual ~MemberObjectT() { printf("MemberObjectT::~MemberObjectT(), this=%p\n", this); }
MemberObjectT &operator=(const MemberObjectT &rhs)
{
printf("MemberObjectT::operator=(const MemberObjectT &rhs), this=%p\n", this);
if (&rhs != this) {}
return *this;
}
MemberObjectT &operator=(MemberObjectT &&rhs)
{
printf("MemberObjectT::operator=(const MemberObjectT &&rhs), this=%p\n", this);
if (&rhs != this) {}
return *this;
}
};
}
template
class BaseT : public Demo::BaseT {
protected:
Demo::MemberObjectT mo;
public:
BaseT() { printf("::BaseT::BaseT(), this=%p\n", this); }
BaseT(const BaseT &rhs) : Demo::BaseT(rhs), mo(rhs.mo) { printf("::BaseT::BaseT(const BaseT &rhs), this=%p\n", this); }
BaseT(BaseT &&rhs) : Demo::BaseT(rhs), mo(rhs.mo) { printf("::BaseT::BaseT(BaseT &&rhs), this=%p\n", this); }
BaseT(T *p) : Demo::BaseT(p) { printf("::BaseT::BaseT(char *p), this=%p\n", this); }
virtual ~BaseT() { printf("::BaseT::~BaseT(), this=%p\n", this); }
BaseT &operator=(const BaseT &rhs)
{
printf("::BaseT::operator=(const BaseT &rhs), this=%p\n", this);
if (&rhs != this) {}
return *this;
}
BaseT &operator=(BaseT &&rhs)
{
printf("::BaseT::operator=(const BaseT &&rhs), this=%p\n", this);
if (&rhs != this) {}
return *this;
}
BaseT operator+(const BaseT &rhs) const
{
printf("::BaseT::operator+(const BaseT &rhs), this=%p\n", this);
BaseT o1;
return o1;
}
};
执行
test_cpp, BaseT>(); 我知道，那么都清楚做法
那么只是不想动手去试，而到处寻找已有的答案而已
这就是我们国家很少有技术创新的根源，中国人多数喜欢吃现成饭，所以测试结果（略）
硬件：Intel® Core™ i5-1035G1
系统：Windows 10 Professional
软件：Microsoft Visual Studio 2015 Enterprise