[英]up casting with CRTP using std::unique_ptr
我指的是這並使用CRTP跟蹤所創建的對象的數量。 但我碰到編譯問題,當我嘗試了鑄Professor
或Student
class
以Person
class
具有std::unique_ptr
。 請參考下面的代碼段,鏈接在這里
#include <iostream>
#include <vector>
#include <memory>
#include <numeric>
#include <exception>
using namespace std;
template<typename T>
class Person
{
public:
Person(string Name="", int Age=0) : name(Name), age(Age)
{
++cur_id;
}
virtual ~Person() {}
virtual void getdata() = 0;
virtual void putdata() = 0;
protected:
string name;
int age;
static int cur_id;
};
template<typename T> int Person<T>::cur_id = 0;
class Professor : public Person<Professor>
{
public:
Professor(string Name="", int Age=0, int Publications=0);
~Professor() {}
void getdata() override;
void putdata() override;
protected:
bool IsValidInput();
private:
int publications;
};
Professor::Professor(string Name, int Age, int Publications) try : Person(Name,Age), publications(Publications)
{
}
// Catch constructor that fails
catch(std::exception & e)
{
std::cout<<"\n Exception - "<<e.what()<<std::endl;
exit(1);
}
bool Professor::IsValidInput()
{
if (name.empty() || (name.length() > 100))
{
return false;
}
if ( age <= 0 || age > 80 )
{
return false;
}
if ( publications <= 0 || publications > 1000)
{
return false;
}
return true;
}
void Professor::getdata()
{
cout<< "Enter Name age publications" << endl;
cin >> name >> age >> publications;
if (!IsValidInput())
{
throw std::invalid_argument("wrong arguments");
}
}
void Professor::putdata()
{
cout << name << " " << age << " " << publications << " " << cur_id << endl;
}
class Student : public Person<Student>
{
public:
Student(string Name="", int Age=0, const vector<int> & Marks = vector<int>());
~Student() {}
void getdata() override;
void putdata() override;
protected:
bool IsValidInput();
private:
vector<int> marks;
static const int TOTAL_MARKS = 5;
};
Student::Student(string Name, int Age, const vector<int> & Marks) try : Person(Name,Age), marks(Marks)
{
}
// Catch constructor that fails
catch(std::exception & e)
{
std::cout<<"\n Exception - "<<e.what()<<std::endl;
exit(1);
}
void Student::getdata()
{
int mark = 0;
cout<< "Enter Name age marks(5)" << endl;
cin >> name >> age;
for (size_t idx = 0; idx < TOTAL_MARKS; ++idx)
{
cin >> mark;
marks.push_back(mark);
}
if (!IsValidInput())
{
throw std::invalid_argument("wrong arguments");
}
}
void Student::putdata()
{
cout << name << " " << age << " " << std::accumulate(marks.begin(),marks.end(),0) << " " << cur_id << endl;
}
bool Student::IsValidInput()
{
if (name.empty() || (name.length() > 100))
{
return false;
}
if ( age <= 0 || age > 80 )
{
return false;
}
for (size_t idx = 0; idx < marks.size(); ++idx)
{
if ( marks[idx] < 0 || marks[idx] > 100 )
{
return false;
}
}
return true;
}
int main()
{
int totalObj = 0, type = 0;
cout<< "Enter total obj : ";
cin >> totalObj;
std::vector<std::unique_ptr<Person<int>>> person;
for (int idx = 0; idx < totalObj; ++idx)
{
cout<< "Enter obj type (1 or 2) : ";
cin >> type;
switch(type)
{
case 1:
{
std::unique_ptr<Person<int>> temp(std::make_unique<Professor>());
temp->getdata();
person.push_back(std::move(temp));
}
break;
case 2:
{
std::unique_ptr<Person<int>> temp(std::make_unique<Student>());
temp->getdata();
person.push_back(std::move(temp));
}
break;
default:
break;
}
}
for (auto itr = person.begin(); itr != person.end(); ++itr)
{
(*itr)->putdata();
}
return 0;
}
問題出在switch case 1 and 2
。 我只是使用int
實例化class Person
。 當我編譯它時,出現以下錯誤
In function 'int main()':
181:80: error: no matching function for call to 'std::unique_ptr<Person<int> >::unique_ptr(std::_MakeUniq<Professor>::__single_object)'
181:80: note: candidates are:
In file included from /usr/include/c++/4.9/memory:81:0,
from 3:
/usr/include/c++/4.9/bits/unique_ptr.h:228:2: note: template<class _Up, class> std::unique_ptr<_Tp, _Dp>::unique_ptr(std::auto_ptr<_Up>&&)
unique_ptr(auto_ptr<_Up>&& __u) noexcept;
^
/usr/include/c++/4.9/bits/unique_ptr.h:228:2: note: template argument deduction/substitution failed:
181:80: note: 'std::_MakeUniq<Professor>::__single_object {aka std::unique_ptr<Professor, std::default_delete<Professor> >}' is not derived from 'std::auto_ptr<_Up>'
In file included from /usr/include/c++/4.9/memory:81:0,
from 3:
請提出如何將Professor and Student
為Person std::unique_ptr
。
您的問題是Student
和Professor
沒有擴展Person<int>
。 實際上, Person<int>
與Professor
無關,每個Person<...>
都是完全不同的類,彼此之間沒有關系。
如果要將所有人員類型保留在向量中,則需要一個多態類,該類在所有Person<...>
上提供一個接口。
您的問題的解決方案是創建一個抽象的人:
struct AbstractPerson {
virtual void getdata() = 0;
virtual void putdata() = 0;
virtual ~AbstractPerson() = default;
};
然后,使Person<T>
從該類繼承:
template<typename T>
struct Person : AbstractPerson {
// ...
};
然后,將不相關的std::vector<Person<int>>
替換為:
std::vector<std::unique_ptr<AbstractPerson>> person;
// ...
person.emplace_back(std::make_unique<Student>()); // works!
這是您工作的實時版本,代碼略有現代化: 在Coliru上實時運行
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