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 个参数 cutter_point-"<<s1<<endl;
}
else
{
os<<"3 个参数 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; //这个是可以加两个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"};
//通过一个临时的函数对象应用<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
我们可以定义一个map，用string类型来关联相应的函数，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，我们可以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
//含有一个很好的办法就是使用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是较早的版本的一部分
标准库。这些类被更一般的结合使用函数取代
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 个参数 cutter_point-"<<s1<<endl;
}
else
{
os<<"3 个参数 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; //这个是可以加两个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"};
//通过一个临时的函数对象应用<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
/*
我们可以定义一个map，用string类型来关联相应的函数，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，我们可以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
//含有一个很好的办法就是使用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是较早的版本的一部分
标准库。这些类被更一般的结合使用函数取代
*/
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点开始，7点起床！！！努力，我要学的东西还很多，远远不够，时间如此紧迫，怎可徒费光阴！！！
时间： 2024-11-03 05:28:21