1、Problom
class GeoNeighborsTimer : public TimerCallback {
public:
GeoNeighborsTimer(GeoRoutingFilter *agent) : agent_(agent) {};
~GeoNeighborsTimer() {};
int expire();
GeoRoutingFilter *agent_;
};
只知道在类后加冒号后跟继承的父类,可这构造函数后跟一个冒号,后边又有类的成员,又有构造函数的参数,这是什么意思呢?
2、Anwser
构造函数后跟冒号
表示先对冒号后的类成员(参数中的哪个)进行初始化,然后做为冒号前类的成员。
class Student {
public:
Student() {}
Student( const string& nm, int sc = 0 )
: name( nm ), score( sc ) {}
//这个跟name=nm ;score=sc;语句效果一样
private:
string name;
int score;
};
关于什么时候得这么用?是不是必须得这么用?和是不是只能用在构造函数?待考证 。。。。
from: c++ primer
Constructors
构造函数
When we create an object of a class type, the compiler automatically uses a constructor (Section 2.3.3, p. 49)
to initialize the object. A constructor is a special member function
that has the same name as the class. Its purpose is to ensure that each
data member is set to sensible initial values.
创建一个类类型的对象时,编译器会自动使用一个构造函数(第 2.3.3 节)来初始化该对象。构造函数是一个特殊的、与类同名的成员函数,用于给每个数据成员设置适当的初始值。
A constructor generally should use a constructor initializer list (Section 7.7.3, p. 263), to initialize the data members of the object:
构造函数一般就使用一个构造函数初始化列表(第 7.7.3 节),来初始化对象的数据成员:
// default constructor needed to initialize members of built-in type Sales_item(): units_sold(0), revenue(0.0) { }
The constructor initializer list is a list of member names and
parenthesized initial values. It follows the constructor's parameter
list and begins with a colon. |