boost学习-3.conversion，多态类型之间的安全转型，与数据类型转换

这个库比较简单，看例子就明白啦

1.多态类型之间的安全转型

polymorphic_cast 和 polymorphic_downcast 

namespace boost {
  

template <class Derived, class Base>
inline Derived polymorphic_cast(Base* x);
// 抛出: std::bad_cast 如果 ( dynamic_cast<Derived>(x) == 0 )
// 返回: dynamic_cast<Derived>(x)

template <class Derived, class Base>
inline Derived polymorphic_downcast(Base* x);
// 效果: assert( dynamic_cast<Derived>(x) == x );
// 返回: static_cast<Derived>(x)

}

#include <boost/cast.hpp>
...
class Fruit { public: virtual ~Fruit(){}; ... };
class Banana : public Fruit { ... };
...
void f( Fruit * fruit ) {
  
// ... 我们确信 fruit 是一个 Banana
  Banana * banana = boost::polymorphic_downcast<Banana*>(fruit);
  ...

2.数据类型转换

lexical_cast<>

#include <iostream>

#include <boost/lexical_cast.hpp>

using namespace boost;

using namespace std;

int main()

{
    

    int i = lexical_cast<int>("123444");

    cout<<"i="<<i<<endl;

    string s = lexical_cast<string>(i);

    cout<<"string s = "<<s<<endl;

    double d1 = 1.345678900;

    s = lexical_cast<string>(d1);

    cout<<"string s = "<<s<<endl;

    return 0;

}