开发工具VC++ 6.0，举例类CEmployee
按照习惯，我们在头文件中如果已经声明了变量，我们在源文件中就可以直接使用了。
1: protected:
2: static string m_EmployeeName;
我们在构造函数初始化它，
1: CEmployee::CEmployee()
2: {
3:
4: m_EmployeeName ="Rock";
5: }
编译没有问题，但连接的时候有问题：
Linking...
Employee.obj : error LNK2001: unresolved external symbol "protected: static class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > CEmployee::m_EmployeeName" (?m_EmployeeName@CEmployee@@1V?$basic_string@DU?$char_trai
ts@D@std@@V?$allocator@D@2@@std@@A)
Debug/TestStaticVariable.exe : fatal error LNK1120: 1 unresolved externals
Error executing link.exe.
正确的申明方式应该做到两点：
1. 在头文件中申明
2. 在源文件中再次声明。
头文件中：
1: private:
2: static string m_EmployeeName;
3: static int m_count;
源文件：
1: string CEmployee::m_EmployeeName;
2: int CEmployee::m_count;
3:
4:
5:
6: CEmployee::CEmployee()
7: {
8:
9: m_EmployeeName ="Rock";
10: m_count++;
11: }
这样的申明方式很容易让人疑惑。
疑惑一：源文件再次申明静态变量不需要再加static前缀。
疑惑二：理论上，静态变量是不可继承的，因此访问方式只能是类的公开或私有。但是，我们把它定义为保护类型编译运行也没有错。
1:
2: protected:
3: static string m_EmployeeName;
4: static int m_count;
5:
我经常使用java或C#, 对于这种违背OO的语法自然有所疑惑. 不过:C++确实是有其与OO不同的语法之处.
为了测试静态变量是否确实像我们想象那样,我定义几个函数,并做了测试.
注意:静态函数的申明也如同静态变量一样.
1: // Employee.h: interface for the CEmployee class.
2: //
3: //////////////////////////////////////////////////////////////////////
4:
5: #if !defined(AFX_EMPLOYEE_H__CD070057_6BC8_4639_BA5B_8EBD94A191BD__INCLUDED_)
6: #define AFX_EMPLOYEE_H__CD070057_6BC8_4639_BA5B_8EBD94A191BD__INCLUDED_
7:
8: #if _MSC_VER > 1000
9: #pragma once
10: #endif // _MSC_VER > 1000
11: #include <iostream>
12: using namespace std;
13:
14: class CEmployee
15: {
16:
17: public:
18: CEmployee();
19: virtual ~CEmployee();
20: static intilizeCount(int in_count);
21: int& getCount();
22:
23:
24:
25: protected:
26: static string m_EmployeeName;
27: static int m_count;
28:
29:
30: };
31:
32: #endif // !defined(AFX_EMPLOYEE_H__CD070057_6BC8_4639_BA5B_8EBD94A191BD__INCLUDED_)
1: // Employee.cpp: implementation of the CEmployee class.
2: //
3: //////////////////////////////////////////////////////////////////////
4:
5: #include "stdafx.h"
6: #include "Employee.h"
7:
8: //////////////////////////////////////////////////////////////////////
9: // Construction/Destruction
10: //////////////////////////////////////////////////////////////////////
11:
12: string CEmployee::m_EmployeeName;
13: int CEmployee::m_count;
14:
15:
16:
17: CEmployee::CEmployee()
18: {
19:
20: m_EmployeeName ="Rock";
21: m_count++;
22: }
23:
24: CEmployee::~CEmployee()
25: {
26:
27: }
28:
29: CEmployee::intilizeCount(int in_count)
30: {
31: m_count = in_count;
32: }
33: int& CEmployee::getCount()
34: {
35: return m_count;
36: }
main文件:
1: // TestStaticVariable.cpp : Defines the entry point for the console application.
2: //
3:
4: #include "stdafx.h"
5: #include "Employee.h"
6: #include <iostream>
7: using namespace std;
8:
9: int main(int argc, char* argv[])
10: {
11: //静态调用,用类的静态函数来初始化静态变量
12: CEmployee::intilizeCount(0);
13:
14:
15: CEmployee empl;
16: printf("Now current instance count: %d ", empl.getCount());
17:
18: CEmployee empl2;
19: printf("Now current instance count: %d ", empl.getCount());
20:
21:
22: CEmployee empl3;
23: printf("Now current instance count: %d ", empl.getCount());
24:
25:
26:
27: cin.get();
28:
29: return 0;
30: }
31:
可以看见,运行正常.