const

1、使用const来定义常量

const int num = 10; //应该在声明时进行初始化,否则该常量的值是不确定的,而且无法修改

2、const与指针

指向常量的指针(const修饰的是指针指向的内容)

  1. //指向常量的指针
  2. double rates[5] = {88.9, 100.12, 59.2, 111.1, 23.2};
  3. const double *pd = rates;
  4. cout << pd[2] << "\n";
  5. pd[2] = 67.99; //error
  6. cout << pd[2];

pd为指向常量的指针,

不能使用pd来修改它指向的数值,但可以让pd指向其他的地址。通常把指向常量的指针用作函数参量。

指针常量(const 修饰指针)

  1. //指针常量
  2. double rates[5] = {88.9, 100.12, 59.2, 111.1, 23.2};
  3. cout << pd[2] << "\n";
  4. double * const pd2 = rates;
  5. pd2[2] = 67.99; //ok
  6. cout << pd[2];

pd2的值不可改变,只能指向最初赋给它的地址,但pd2可以用来改变它所指向的数据值。

<<effective C++>>上有个好记的方法:const在*号左边修饰的是指针所指的内容;const在*号右边修饰的是指针。
简单记就是:左内容,右指针。
也可以这样理解:先忽略类型名,然后看const离哪个近,就修饰谁。
如:const [int] *p; //先去掉int,这时const 修饰*p, p是指针,*p是指针指向的对象,不可变。

3、const与引用

double value = 100;

const double & v = value;

不能修改const引用所指向的内容

4、const与类成员

  1. class StaticAndConstTest
  2. {
  3. public:
  4. StaticAndConstTest(int _num = 100);
  5. ~StaticAndConstTest(void);
  6. //类的const 成员常量 必须在构造方法中使用初始化列表来初始化
  7. const int num;
  8. };
  9.  
  10. StaticAndConstTest::StaticAndConstTest(int _num)
  11. : num(_num)
  12. {
  13. }

 const成员函数

  1. class StaticAndConstTest
  2. {
  3. public:
  4. StaticAndConstTest(int _num = 100);
  5. ~StaticAndConstTest(void);
  6. //const成员函数
  7. void show() const;
  8. //类的const 成员 必须在构造方法中使用初始化列表来初始化
  9. const int num;
  10. };
  11.  
  12. void StaticAndConstTest::show() const
  13. {
  14. std::cout << num;
  15. }

const成员函数不能修改调用对象,只要类方法不修改调用对象,就应将其声明为const。

static

1、static局部变量

  1. void test()
  2. {
  3. //static 局部变量 在程序的整个生命周期存在,只有一份,作用域为函数局部
  4. static int num = 1000;
  5. num++;
  6. cout << "num=" << num << "\n";
  7. }
  8. int _tmain(int argc, _TCHAR* argv[])
  9. {
  10. for (int i = 0; i < 3; i++)
  11. {
  12. test();
  13. }
  14.  
  15. return 0;
  16. }

输出结果:

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" alt="" />

静态局部变量属于静态存储方式,在函数内定义它的生存期为整个程序生命周期,但是其作用域仍与自动变量相同,只能在定义该变量的函数内使用该变量。
若在声明时未赋以初值,则系统自动赋予0值。而对自动变量不赋初值,则其值是不定的。

2、static全局变量

//静态全局变量 只能在定义它的文件中使用,外部无法访问
static int g_NUM = 100;
非静态全局变量的作用域是整个源程序,也即在各个源文件中都是有效的。

3、static与类

static数据成员与static成员函数函数

  1. class StaticAndConstTest
  2. {
  3. public:
  4. StaticAndConstTest(int _num = 100);
  5. ~StaticAndConstTest(void);
  6. //const成员函数
  7. void show() const;
  8. //静态成员函数 属于类,
  9. //无法访问属于类对象的no-static数据成员,也无法访问no-static成员函数,它只能调用其余的静态成员函数。
  10. static double GetNum();
  11. //类的const 成员 必须在构造方法中使用初始化列表来初始化
  12. const int num;
  13. //类的静态成员变量,属于类,所有类对象共享
  14. static double NUM_2;
  15. //静态成员常量
  16. static const double NUM_3;
  17. //静态成员是整型const可以在类声明中初始化,其他类型不可以
  18. static const int NUM_4 = 4;
  19.  
  20. };
  21.  
  22. //静态全局变量 只能在定义它的文件中使用,外部无法访问
  23. static int g_NUM = 100;
  24. //静态成员变量在类声明中声明,只能在类定义方法的文件中初始化
  25. double StaticAndConstTest::NUM_2 = 100.1;
  26. //静态成员常量
  27. const double StaticAndConstTest::NUM_3 = 200.1;

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