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effective c++ 条款4 make sure that objects are initialized before they are used

1 c++ 类的数据成员的初始化发生在构造函数前

class InitialData{    public:         int data1;         int data2;                 InitialData(int a, int b)        {            data1 = a; //this is assignment            data2 = b; //this is assignment        }       /*       InitialData(int a, int b):data1(a),data2(b) //this is initial       {}      */}

 2 不同cpp文件中的static变量初始化顺序不确定,千万不要互相引用

     比如有个 FileSystem类

class FileSystem{  public:     ...     int getDiskNum() const;}
extern FileSystem tfs;//in the hfile, used in the future for some other class

 然后在一个叫global.cpp文件中申明了一个全局 FileSystem tfs;

然后有个Directory类用到tfs

#include "FileSystem.h"class Directory{public:	Directory()	{		int t=tfs.numDisks();	}};

 有个人需要用Directory类,于是他申明

Directory tmpDir;这时就出现问题,tmpDir初始化时需要用到tfs,单编译器不能保证在编译tmpDir之前编译tfs,于是就会出现编译错误。

解决方案是采用singleton模式,利用函数得到全局变量

FileSystem& getFileSystem{    static FileSystem tfs;    return tfs;}

 在Directory要调用tfs时用这个函数

#include "FileSystem.h"class Directory{public:	Directory()	{		int t=getFileSystem();	}};