【足迹C++primer】48、函数引用操作符

函数引用操作符

struct absInt
{
    int operator()(int val) const
    {
        cout<<val<<"<->!!!"<<endl;
        return val<0 ? -val : val;
    }
};

void fun1()
{
    int i=-42;
    absInt absObj;
    int ui=absObj(i);
}

Function-Object Classes with State

函数对象类的状态

class PrintString
{
public:
    PrintString(ostream &o=cout, char c=' '):os(o), sep(c) {}   //构造函数
    void operator()(const string &s) const {os<<">>>>-----<<<<"<<s<<sep<<"yeah!"<<endl;}   //函数操纵符
    void operator()(const int i, const string &s1, const string &s2) const
    {
        if(i)
        {
            os<<"3 个參数 cutter_point-"<<s1<<endl;
        }
        else
        {
            os<<"3 个參数 cutter_point-"<<s2<<endl;
        }
    }

private:
    ostream &os;    //输出流
    char    sep;
};

void fun2()
{
    string s="cutter_point";
    PrintString printer;        //默认构造函数
    printer(s);     //调用操作符函数,输出:>>>>-----<<<<cutter_point yeah!
    PrintString errors(cerr, '\n'); //上面yeah!前面变成换行
    errors(s);

    vector<string> vs;
    for(size_t i=0 ; i != 7 ; ++i)
    {
        stringstream ss;
        ss<<i<<"-cutter_point";
        vs.push_back(ss.str());
    }
    for_each(vs.begin(), vs.end(), PrintString(cerr, '\n'));

    PrintString three;
    three(1, "我就是这么屌！", "没有，也就一般般啦！");
}

14.8.1. Lambdas Are Function Objects

void fun3()
{
    vector<string> words;
    for(size_t i=0 ; i != 7 ; ++i)
    {
        stringstream ss;
        ss<<i<<"-cutter_point";
        words.push_back(ss.str());
    }
    stable_sort(words.begin(), words.end(), [](const string &a, const string &b){return a.size()<b.size();});
    for_each(words.begin(), words.end(), PrintString(cout, '3'));
}

class ShorterString
{
public:
    bool operator()(const string &s1, const string &s2) const
    {return s1.size()<s2.size(); }
};

void fun4()
{
    vector<string> words;
    for(size_t i=8 ; i != -1 ; --i)
    {
        stringstream ss;
        ss<<i<<"-cutter_point";
        words.push_back(ss.str());
    }
    words.push_back("test排序");

    stable_sort(words.begin(), words.end(), ShorterString());
    for(vector<string>::iterator it=words.begin() ; it != words.end() ; ++it)
        cout<<*it<<"\t";
}

Classes Representing Lambdas with Captures

void fun5()
{
    vector<string> words;
    vector<string>::size_type sz=5;
    for(size_t i=8 ; i != -1 ; --i)
    {
        stringstream ss;
        ss<<i<<"-cutter_point";
        words.push_back(ss.str());
    }
    words.push_back("test排序");

    //得到一个指向第一个s.size()>sz的元素
    auto wc=find_if(words.begin(), words.end(), [sz](const string &a){return a.size() >= sz;});
    for(vector<string>::iterator it=words.begin() ; it != words.end() ; ++it)
        cout<<*it<<"\t";
    if(wc != words.end())
    {
        cout<<"wc:"<<*wc<<endl;
    }

}

class SizeComp
{
public:
    SizeComp(size_t n):sz(n) {} //构造函数
    bool operator()(const string &s) const {return s.size()>=sz;}
private:
    size_t sz;
};

void fun6()
{
    vector<string> words;
    vector<string>::size_type sz=6;
    for(size_t i=8 ; i != -1 ; --i)
    {
        stringstream ss;
        ss<<i<<"-cutter_point";
        words.push_back(ss.str());
    }
    words.push_back("test排序");

    //得到一个指向第一个s.size()>sz的元素
    auto wc=find_if(words.begin(), words.end(), SizeComp(sz));
    ///这里为什么会引用operator()操作呢？？

    cout<<endl;
    if(wc != words.end())
    {
        cout<<"wc:"<<*wc<<endl;
    }
}

14.8.2. Library-Defined Function Objects

void fun7()
{
    plus<int> intAdd;       //这个是能够加两个int型数字
    negate<int> intNegate;  //求相反数
    int sum=intAdd(10, 20); //结果30
    cout<<sum<<endl;
    sum=intNegate(intAdd(10, 20));  //结果-30
    cout<<sum<<endl;
    sum=intAdd(10, intNegate(10));  //结果0
    cout<<sum<<endl;
}

Using a Library Function Object with the Algorithms

void fun8()
{
    vector<string> svec={"i","like","china","so","much","I","can","just","do","it"};
    //通过一个暂时的函数对象应用<操作对两个string
    sort(svec.begin(), svec.end(), greater<string>());
    //输出结果按字典位置排序，然后大写在后,递减排序
    for_each(svec.begin(), svec.end(), [](string &s){cout<<s<<"\t";});
}

通过指针直接操作内存的地址，来改变排序

void fun9()
{
    vector<string> svec={"i","like","china","so","much","I","can","just","do","it"};
    vector<string*> nameTable;
    for(vector<string>::iterator it=svec.begin() ; it != svec.end() ; ++it)
    {
        string* s=new string;   //这里new string一定要加！！,为了给s分配空间
        *s=*it;
        nameTable.push_back(s);
    }

//    sort(nameTable.begin(), nameTable.end(), [](string* a, string* b){return a<b;});
    sort(nameTable.begin(), nameTable.end(), less<string*>());
    //输出的是按内存位置来输出的
    for(vector<string*>::iterator it=nameTable.begin() ; it != nameTable.end() ; ++it)
        cout<<*(*it)<<"\t";
}

14.8.3. Callable Objects and function

可调用对象和函数

Different Types Can Have the Same Call Signature

int add(int i, int j) {return i+j;}
void fun10()
{
    auto mod=[](int i, int j){return i%j;};
}
struct div2 //这里不要用div好像是和stdlib.h冲突了
{
    int operator()(int denominator, int divisor){return denominator/divisor;}
};

//上面三个都是int(int, int)类型的

我们能够定义一个map，用string类型来关联对应的函数，用string作为标识

void fun11()
{
    auto mod=[](int i, int j){return i%j;};
    map<string, int(*)(int, int)> binops;   //这是一个函数指针,返回一个int类型
    //这里add是一个指向+运算的指针,div是不能这样加的，它不是指针
    binops.insert({"+", add});
    binops.insert({"%", mod});
//    binops.insert({"/", div2});
}

库函数类型

void fun12()
{
    function<int(int, int)> f1=add;     //函数指针,这个是加法
    function<int(int, int)> f2=div2();   //调用()操作符,这个是除法
    function<int(int, int)> f3=[](int i, int j) {return i*j;};  //lambda返回乘法
    cout<<f1(4,2)<<endl;    //6
    cout<<f2(4,2)<<endl;    //2
    cout<<f3(4,2)<<endl;    //8
}

void fun13()
{
    auto mod=[](int i, int j){return i%j;};
    map<string, function<int(int, int)>> binops=
    {
        {"+", add},{"-", std::minus<int>()},{"/", div2()},{"*", [](int i, int j){return i*j;}},
        {"%", mod}
    };  //这个map有五个元素，当我们索引这个map的时候，我们能够调用这五个函数类型

    cout<<"+ <--->"<<binops["+"](10, 5)<<endl;
    cout<<"- <--->"<<binops["-"](10, 5)<<endl;
    cout<<"/ <--->"<<binops["/"](10, 5)<<endl;
    cout<<"* <--->"<<binops["*"](10, 5)<<endl;
    cout<<"% <--->"<<binops["%"](10, 5)<<endl;
}

Overloaded Functions and function

重载的函数和功能

void fun14()
{
    map<string, function<int(int, int)>> binops;
    int (*fp)(int, int)=add;
    binops.insert({"+", fp});   //用函数指针来避免重载,或者同名函数的含糊不清
    //含有一个非常好的办法就是使用lambda来消除歧义是非常好的
    binops.insert({"+", [](int a, int b){return add(a,b);}});

}

在新的库函数类是不相关的类命名为

unary_function和binary_function是较早的版本号的一部分

标准库。这些类被更一般的结合使用函数代替

全代码！

/**
* 功能:函数引用操作符
* 时间:2014年7月18日16:11:45
* 作者:cutter_point
*/

#include<iostream>
#include<cstring>
#include<vector>
#include<algorithm>
#include<sstream>
#include<string>
#include<map>
#include<functional>

using namespace std;

struct absInt
{
    int operator()(int val) const
    {
        cout<<val<<"<->!!!"<<endl;
        return val<0 ? -val : val;
    }
};

void fun1()
{
    int i=-42;
    absInt absObj;
    int ui=absObj(i);
}

/**
Function-Object Classes with State
函数对象类的状态
*/
class PrintString
{
public:
    PrintString(ostream &o=cout, char c=' '):os(o), sep(c) {}   //构造函数
    void operator()(const string &s) const {os<<">>>>-----<<<<"<<s<<sep<<"yeah!"<<endl;}   //函数操纵符
    void operator()(const int i, const string &s1, const string &s2) const
    {
        if(i)
        {
            os<<"3 个參数 cutter_point-"<<s1<<endl;
        }
        else
        {
            os<<"3 个參数 cutter_point-"<<s2<<endl;
        }
    }

private:
    ostream &os;    //输出流
    char    sep;
};

void fun2()
{
    string s="cutter_point";
    PrintString printer;        //默认构造函数
    printer(s);     //调用操作符函数,输出:>>>>-----<<<<cutter_point yeah!
    PrintString errors(cerr, '\n'); //上面yeah!前面变成换行
    errors(s);

    vector<string> vs;
    for(size_t i=0 ; i != 7 ; ++i)
    {
        stringstream ss;
        ss<<i<<"-cutter_point";
        vs.push_back(ss.str());
    }
    for_each(vs.begin(), vs.end(), PrintString(cerr, '\n'));

    PrintString three;
    three(1, "我就是这么屌！", "没有，也就一般般啦！");
}

/**
14.8.1. Lambdas Are Function Objects
*/
void fun3()
{
    vector<string> words;
    for(size_t i=0 ; i != 7 ; ++i)
    {
        stringstream ss;
        ss<<i<<"-cutter_point";
        words.push_back(ss.str());
    }
    stable_sort(words.begin(), words.end(), [](const string &a, const string &b){return a.size()<b.size();});
    for_each(words.begin(), words.end(), PrintString(cout, '3'));
}

class ShorterString
{
public:
    bool operator()(const string &s1, const string &s2) const
    {return s1.size()<s2.size(); }
};

void fun4()
{
    vector<string> words;
    for(size_t i=8 ; i != -1 ; --i)
    {
        stringstream ss;
        ss<<i<<"-cutter_point";
        words.push_back(ss.str());
    }
    words.push_back("test排序");

    stable_sort(words.begin(), words.end(), ShorterString());
    for(vector<string>::iterator it=words.begin() ; it != words.end() ; ++it)
        cout<<*it<<"\t";
}

/**
Classes Representing Lambdas with Captures
*/
void fun5()
{
    vector<string> words;
    vector<string>::size_type sz=5;
    for(size_t i=8 ; i != -1 ; --i)
    {
        stringstream ss;
        ss<<i<<"-cutter_point";
        words.push_back(ss.str());
    }
    words.push_back("test排序");

    //得到一个指向第一个s.size()>sz的元素
    auto wc=find_if(words.begin(), words.end(), [sz](const string &a){return a.size() >= sz;});
    for(vector<string>::iterator it=words.begin() ; it != words.end() ; ++it)
        cout<<*it<<"\t";
    if(wc != words.end())
    {
        cout<<"wc:"<<*wc<<endl;
    }

}

class SizeComp
{
public:
    SizeComp(size_t n):sz(n) {} //构造函数
    bool operator()(const string &s) const {return s.size()>=sz;}
private:
    size_t sz;
};

void fun6()
{
    vector<string> words;
    vector<string>::size_type sz=6;
    for(size_t i=8 ; i != -1 ; --i)
    {
        stringstream ss;
        ss<<i<<"-cutter_point";
        words.push_back(ss.str());
    }
    words.push_back("test排序");

    //得到一个指向第一个s.size()>sz的元素
    auto wc=find_if(words.begin(), words.end(), SizeComp(sz));
    ///这里为什么会引用operator()操作呢？？

    cout<<endl;
    if(wc != words.end())
    {
        cout<<"wc:"<<*wc<<endl;
    }
}

/**************************************
14.8.2. Library-Defined Function Objects
**************************************/
void fun7()
{
    plus<int> intAdd;       //这个是能够加两个int型数字
    negate<int> intNegate;  //求相反数
    int sum=intAdd(10, 20); //结果30
    cout<<sum<<endl;
    sum=intNegate(intAdd(10, 20));  //结果-30
    cout<<sum<<endl;
    sum=intAdd(10, intNegate(10));  //结果0
    cout<<sum<<endl;
}

/**************************************
Using a Library Function Object with the Algorithms
**************************************/
void fun8()
{
    vector<string> svec={"i","like","china","so","much","I","can","just","do","it"};
    //通过一个暂时的函数对象应用<操作对两个string
    sort(svec.begin(), svec.end(), greater<string>());
    //输出结果按字典位置排序，然后大写在后,递减排序
    for_each(svec.begin(), svec.end(), [](string &s){cout<<s<<"\t";});
}

//通过指针直接操作内存的地址，来改变排序
void fun9()
{
    vector<string> svec={"i","like","china","so","much","I","can","just","do","it"};
    vector<string*> nameTable;
    for(vector<string>::iterator it=svec.begin() ; it != svec.end() ; ++it)
    {
        string* s=new string;   //这里new string一定要加！！,为了给s分配空间
        *s=*it;
        nameTable.push_back(s);
    }

//    sort(nameTable.begin(), nameTable.end(), [](string* a, string* b){return a<b;});
    sort(nameTable.begin(), nameTable.end(), less<string*>());
    //输出的是按内存位置来输出的
    for(vector<string*>::iterator it=nameTable.begin() ; it != nameTable.end() ; ++it)
        cout<<*(*it)<<"\t";
}

/**************************************
14.8.3. Callable Objects and function
可调用对象和函数
**************************************/

/**
Different Types Can Have the Same Call Signature
*/
int add(int i, int j) {return i+j;}
void fun10()
{
    auto mod=[](int i, int j){return i%j;};
}
struct div2 //这里不要用div好像是和stdlib.h冲突了
{
    int operator()(int denominator, int divisor){return denominator/divisor;}
};

//上面三个都是int(int, int)类型的

/*
我们能够定义一个map，用string类型来关联对应的函数，用string作为标识
*/
void fun11()
{
    auto mod=[](int i, int j){return i%j;};
    map<string, int(*)(int, int)> binops;   //这是一个函数指针,返回一个int类型
    //这里add是一个指向+运算的指针,div是不能这样加的，它不是指针
    binops.insert({"+", add});
    binops.insert({"%", mod});
//    binops.insert({"/", div2});
}

/**
库函数类型
*/
void fun12()
{
    function<int(int, int)> f1=add;     //函数指针,这个是加法
    function<int(int, int)> f2=div2();   //调用()操作符,这个是除法
    function<int(int, int)> f3=[](int i, int j) {return i*j;};  //lambda返回乘法
    cout<<f1(4,2)<<endl;    //6
    cout<<f2(4,2)<<endl;    //2
    cout<<f3(4,2)<<endl;    //8
}

void fun13()
{
    auto mod=[](int i, int j){return i%j;};
    map<string, function<int(int, int)>> binops=
    {
        {"+", add},{"-", std::minus<int>()},{"/", div2()},{"*", [](int i, int j){return i*j;}},
        {"%", mod}
    };  //这个map有五个元素，当我们索引这个map的时候，我们能够调用这五个函数类型

    cout<<"+ <--->"<<binops["+"](10, 5)<<endl;
    cout<<"- <--->"<<binops["-"](10, 5)<<endl;
    cout<<"/ <--->"<<binops["/"](10, 5)<<endl;
    cout<<"* <--->"<<binops["*"](10, 5)<<endl;
    cout<<"% <--->"<<binops["%"](10, 5)<<endl;
}

/**
Overloaded Functions and function
重载的函数和功能
*/
void fun14()
{
    map<string, function<int(int, int)>> binops;
    int (*fp)(int, int)=add;
    binops.insert({"+", fp});   //用函数指针来避免重载,或者同名函数的含糊不清
    //含有一个非常好的办法就是使用lambda来消除歧义是非常好的
    binops.insert({"+", [](int a, int b){return add(a,b);}});

}

/*
在新的库函数类是不相关的类命名为
unary_function和binary_function是较早的版本号的一部分
标准库。这些类被更一般的结合使用函数代替
*/

int main()
{
    cout<<">>----------------fun1---------------------<<"<<endl;
    fun1();
    cout<<">>----------------fun2---------------------<<"<<endl;
    fun2();
    cout<<">>----------------fun3---------------------<<"<<endl;
    fun3();
    cout<<">>----------------fun4---------------------<<"<<endl;
    fun4();
    cout<<">>----------------fun5---------------------<<"<<endl;
    fun5();
    cout<<">>----------------fun6---------------------<<"<<endl;
    fun6();
    cout<<">>----------------fun7---------------------<<"<<endl;
    fun7();
    cout<<">>----------------fun8---------------------<<"<<endl;
    fun8();
    cout<<">>----------------fun9---------------------<<"<<endl;
    fun9();
    cout<<">>----------------fun12---------------------<<"<<endl;
    fun12();
    cout<<">>----------------fun13---------------------<<"<<endl;
    fun13();

    system("pause");
    return 0;
}

PS：今天早上有点晚了，不行，以后每天早上坚持至少8点開始，7点起床！！！努力，我要学的东西还非常多，远远不够，时间如此紧迫，怎可徒费光阴！！！