在C ++中从用户定义类型到原始类型的隐式转换

本文介绍了在C ++中从用户定义类型到原始类型的隐式转换的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我能够找到很多有关从隐式转换(例如，从int到用户定义类型)的信息.即，如果构造函数将int作为其参数，并且未以显式"作为前缀，则可能会发生隐式转换.

I am able to find plenty of information about implicit conversion from, say, an int to a user defined type. i.e. if a constructor takes an int as its parameter and is not prefaced by "explicit" then implicit conversions can occur.

如果我希望我的班级将隐式转换为一个整数怎么办?

What if I want my class to implicitly convert to an int?

例如，需要在SimpleClass的内部或外部添加什么函数，以便主函数可以编译并向控制台输出"1"?(请参阅评论)

For example, what function needs to be added either inside or outside of SimpleClass such that the main function will compile and output "1" to the console? (see comments)

#include <iostream> class SimpleClass { private: int m_int; public: SimpleClass(int value) : m_int(value) {} }; int main(int argc, const char * argv[]) { SimpleClass simpleclass(1); int i = simpleclass; // does not complile std::cout << i << std::endl; // should output "1" to the console return 0; }

推荐答案

隐式转换可以通过两种方式定义:

Implicit conversions can be defined in two ways:

• 非显式单参数构造函数.
• 非显式转换函数(又称转换运算符)，N3337 12.3.2

后面的代码允许定义从类类型到原始类型的转换.只需添加

The later allows defining conversion from class type to primitive type. Just add

class SimpleClass { // ... operator int() const; }; SimpleClass::operator int() const { return m_int; }