Chapter Summary

小结

Functions are named units of computation and are essential to structuring even modest programs. They are defined by specifying a return type, a name, a (possibly empty) list of parameters, and a function body. The function body is a block that is executed when the function is called. When a function is called, the arguments passed to the function must be compatible with the types of the corresponding parameters.

函数是有名字的计算单元，对程序（就算是小程序）的结构化至关重要。函数的定义由返回类型、函数名、形参表（可能为空）以及函数体组成。函数体是调用函数时执行的语句块。在调用函数时，传递给函数的实参必须与相应的形参类型兼容。

Passing an argument to a function follows the same rules as initializing a variable. Each parameter that has nonreference type is initialized as a copy of the corresponding argument. Any changes made to a (nonreference) parameter are made to the local copy, not to the argument itself.

给函数传递实参遵循变量初始化的规则。非引用类型的形参以相应实参的副本初始化。对（非引用）形参的任何修改仅作用于局部副本，并不影响实参本身。

Copying large, complex values can be expensive. To avoid the overhead of passing a copy, parameters can be specified as references. Changes made to reference parameters are reflected in the argument itself. A reference parameter that does not need to change its argument should be const reference.

复制庞大而复杂的值有昂贵的开销。为了避免传递副本的开销，可将形参指定为引用类型。对引用形参的任何修改会直接影响实参本身。应将不需要修改相应实参的引用形参定义为 const 引用。

In C++, functions may be overloaded. The same name may be used to define different functions as long as the number or types of the parameters in the functions differ. The compiler automatically figures out which function to call based the arguments in a call. The process of selecting the right function from a set of overloaded functions is referred to as function matching.

在 C++ 中，函数可以重载。只要函数中形参的个数或类型不同，则同一个函数名可用于定义不同的函数。编译器将根据函数调用时的实参确定调用哪一个函数。在重载函数集合中选择适合的函数的过程称为函数匹配。

C++ provides two special kinds of functions: inline and member functions. Specifying inline on a function is a hint to the compiler to expand the function into code directly at the call point. Inline functions avoid the overhead associated with calling a function. Member functions are just that: class members that are functions. This chapter introduced simple member functions. Chapter 12 will cover member functions in more detail.

C++ 提供了两种特殊的函数：内联函数和成员函数。将函数指定为内联是建议编译器在调用点直接把函数代码展开。内联函数避免了调用函数的代价。成员函数则是身为类成员的函数。本章介绍了简单的成员函数，在第十二章将会更详细地介绍成员函数。