什么时候使用动态的可接受示例
这个问题在这里已经有了答案：
@ user997112
[在底部编辑]
你好。 下面我们使用具有共同祖先的随机多态指针集合
通过通用接口。
额外的工作是使用其中一个特定派生类完成的
我们需要dynamic_cast或typeid来了解这个....
主要功能有呼叫
然后是类声明
那么动态演员阵容就结束了
没有显示用new创建的对象的删除
#include <iostream>
#include <algorithm>
#include <random>
#include <exception>
using namespace std;
int dynamic_test();
int main()
{
cout << "Hello world!" << endl;
dynamic_test();
return 0;
}
............
class basex {
public:
virtual ~basex() {};
virtual void work() const = 0;
};
class next1x : public basex {
public:
void work() const override {cout << "1";/*secret*/}
};
class next2x : public basex {
public:
void work() const override {cout << "2";/*secret*/}
};
class next3x : public basex {
public:
void work() const override {cout << "3";/*secret*/}
};
std::vector<basex *> secret_class_picker()
{
//pick classes with common base at random
std::random_device rd;
std::uniform_int_distribution<int> ud(1,3);
std::mt19937 mt(rd());
std::vector<int> random_v;
for (int i = 0; i < 22; ++i)
random_v.push_back( ud(mt) );
cout << "Random" << endl;
for ( auto bq : random_v) //inspecting for human reader
cout << bq << " ";
std::vector<basex *> v;
basex * bptr;
for (auto bq : random_v) {
switch(bq)
{
default: throw std::exception(); break;
case 1: bptr = new next1x; break;
case 2: bptr = new next2x; break;
case 3: bptr = new next3x; break;
}
v.push_back(bptr);
}
cout << "Objects Created " << v.size() << endl;
return v;
}
//this function demands a more derived class
int special_work(const next3x *)
{
//elided
cout <<"[!]";
return 0;
}
int dynamic_test()
{
std::vector<basex *> v = secret_class_picker();//delete these pointer later
cout <<"Working with random polymorphic pointers"<<endl;
for (const auto bq : v)
{
bq->work();//polymorphic
next3x * ptr = dynamic_cast<next3x *>(bq);
if (nullptr != ptr) special_work(ptr); //reserved for particular type
}
return 0;
}
......................另类
int dynamic_static_typeid()
{
std::vector<basex *> v = secret_class_picker();
cout <<"Working with random polymorphic pointers"<<endl;
int k(0);
for (const auto bq : v)
{
bool flipflop = (k % 2) == 0;
bq->work();//polymorphic
//cout << "[*]"<< typeid(*bq).name();//dereference
if (flipflop) {
next3x * dc_ptr = dynamic_cast<next3x *>(bq);//not constant time in general
if (nullptr != dc_ptr) {
special_work(dc_ptr); //reserved for particular type
++k;
}
}
else {
if (typeid(next3x) == typeid(*bq)){//constant time
auto sc_ptr = static_cast<next3x *>(bq);//constant time
special_work(sc_ptr);
++k; cout <<"[sc]";
}
}
cout << endl;
}
return 0;
}