#include<iostream>
#include<string>class Entity
{
public:std::string name;int age;Entity(int x) {age = x;}Entity(std::string x){name = x;}
};
void PrintEntity(Entity e)
{std::cout << e.age << ":" << e.name << std::endl;
}
int main()
{PrintEntity(20);    //隐式转换，调用Entity(int x)构造函数将20隐式转换为Entity对象PrintEntity(std::string("pcop"));    //隐式转换，调用Entity(std::string x)构造函数将"20"pcop"隐式转换为Entity对象std::cin.get();return 0;
}

#include<iostream>
#include<string>class Entity
{
public:std::string name;int age;Entity(int x) {age = x;}Entity(std::string x){name = x;}
};
void PrintEntity(Entity e)
{std::cout << e.age << ":" << e.name << std::endl;
}
int main()
{PrintEntity(20);    //隐式转换，调用Entity(int x)构造函数将20隐式转换为Entity对象PrintEntity(std::string("pcop"));    //隐式转换，调用Entity(std::string x)构造函数将"20"pcop"隐式转换为Entity对象PrintEntity("pcop");  //报错，因为pcop时const char*类型的，编译器调用隐式转换将时const char*类型转换为string，但仅能隐式转换一次，故编译器不能将string类型隐式转换为Entity类型std::cin.get();return 0;
}

explicit关键字放在构造函数前面，意味着该构造函数不允许进行隐式转换。示例如下：

#include<iostream>
#include<string>class Entity
{
public:std::string name;int age;explicit Entity(int x) {age = x;}Entity(std::string x){name = x;}
};
void PrintEntity(Entity e)
{std::cout << e.age << ":" << e.name << std::endl;
}
int main()
{PrintEntity(20);    //不能进行隐式转换，因为调用Entity(int x)构造函数前面有explicit关键字PrintEntity(std::string("pcop"));    //隐式转换，调用Entity(std::string x)构造函数将"20"pcop"隐式转换为Entity对象std::cin.get();return 0;
}