【足迹C++primer】48、函数引用操作符

2021-08-29 20:35:15

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";

}

【足迹C++primer】48、函数引用操作符

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;

    }

}

【足迹C++primer】48、函数引用操作符

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";

}

【足迹C++primer】48、函数引用操作符

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;

}

【足迹C++primer】48、函数引用操作符

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！！！

码农公寓

Function-Object Classes with State 函数对象类的状态

14.8.1. Lambdas Are Function Objects

Classes Representing Lambdas with Captures

14.8.2. Library-Defined Function Objects

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

Different Types Can Have the Same Call Signature

库函数类型

Overloaded Functions and function 重载的函数和功能

全代码！

相关文章

Function-Object Classes with State

函数对象类的状态

14.8.3. Callable Objects and function

可调用对象和函数

Overloaded Functions and function

重载的函数和功能