#include "all.h"

/*

* 尽可能使用const

*

* */

class Widget2;

char greeting[] = "ch3";

char *p = greeting;

const char *pp = greeting;

char *const ppp = greeting;

const char *const pppp = greeting;

void f0(const Widget2 *pw); //2种方式作用相同。等价

void f1(Widget2 const *pw);

void f2()

{

std::vector<int> vec;

const std::vector<int>::iterator iter = vec.begin();

*iter = 10; //ok,改变iter指向的内容

// ++iter;//错误，iter 是const

std::vector<int>::const_iterator citer = vec.begin();

//*citer=10; //错误，citer指向的是const对象

++citer; //ok ，citer本身不是const

}

class Rational

{

};

const Rational operator*(const Rational &hls, const Rational &rhs);//返回const对象

//p19

class TextBlock

{

public:

TextBlock(std::string s)

{

text = s;

}

const char &operator[](std::size_t position) const

{

std::cout << "\n调用const版本[]: ";

return text[position];

}

char &operator[](std::size_t position)

{

std::cout << "\n调用non-const版本[]: ";

return text[position];

}

private:

std::string text;

};

void f3()

{

TextBlock tb("hello");

std::cout << tb[0]; //重载了[]运算符

const TextBlock ctb(" world"); //调用const版本

std::cout << ctb[1];

}

void f4(const TextBlock &ctb)

{

// ctb[0]='y'; //错误，ctb[0]返回const对象，故不能修改

std::cout << ctb[0] << ctb[1] << ctb[2];

};

void f5(TextBlock &tb)

{

tb[0] = 'Z'; //正确，tb[0]返回非const对象，string[0]可修改！

//std::cout << std::endl<<tb[0]<<std::endl<<tb[1]<<std::endl<<tb[2];

std::cout << tb[0] << tb[1] << tb[2] << std::endl;

printf("%c ,%c ,", tb[0], tb[1]);

printf("%c ,%c ,", tb[2], tb[3]);

}

int main()

{

f3();

TextBlock tb("hello");

f4(tb);

f5(tb);

return 0;

}