1、适配器

2、函数适配器

#include <iostream>
using namespace std;

#include <algorithm>
#include <vector>
#include <functional>

bool isOdd(int n)
{
    return n % 2 == 1;
}
int main() {
    int a[] = {1, 2, 3, 4, 5};
    vector <int> v(a, a + 5);

    cout << count_if(v.begin(), v.end(), isOdd) << endl;

    // binder2nd将二元函数对象modulus转换为医院函数对象。
    // binder2nd(op, value)(param)相当于op(param, value)
    cout << count_if(v.begin(), v.end(), binder2nd(modulus<int>(), 2)) << endl;

    // binder1st(op, value)(param)相当于op(value, param)
    cout << count_if(v.begin(), v.end(), binder1st(less<int>(), 4)) << endl;
    return 0;
}

// 输出
3
3
1

3、针对成员函数的函数适配器

#include <iostream>
using namespace std;

#include <algorithm>
#include <vector>
#include <functional>
#include <string>

class Person
{
public:
    Person(const string& name) : name_(name)
    {

    }

    void print() const
    {
        cout << name_ << endl;
    }
    void printWithPrefix(string prefix) const
    {
        cout << prefix << name_ << endl;
    }

private:
    string name_;
};

void foo(const vector<Person>& v)
{
    for_each(v.begin(), v.end(), mem_fun_ref(&Person::print));
    for_each(v.begin(), v.end(), binder2nd(mem_fun_ref(&Person::printWithPrefix), "Person: "));
}

void foo2(const vector<Person*>& v)
{
    for_each(v.begin(), v.end(), mem_fun(&Person::print));
    for_each(v.begin(), v.end(), binder2nd(mem_fun(&Person::printWithPrefix), "Person: "));
}
int main() {
    vector<Person> v;
    v.push_back(Person("tom"));
    v.push_back(Person("jer"));
    foo(v);

    vector<Person*> v2;
    v2.push_back(new Person("tom"));
    v2.push_back(new Person("jer"));
    foo2(v2);
    return 0;
}

// 输出
tom
jer
Person: tom
Person: jer
tom
jer
Person: tom
Person: jer

4、针对一般函数的函数适配器

#include <iostream>
using namespace std;

#include <algorithm>
#include <vector>
#include <functional>
#include <string>
#include <cstring>

int main() {
    char* a[] = {"", "BBB", "CCC"};
    vector<char*> v(a, a + 2);
    vector<char*>::iterator it;
    it = find_if(v.begin(), v.end(), binder2nd(ptr_fun(strcmp), ""));
    if (it != v.end())
    {
        cout << *it << endl;
    }
    return 0;
}
// 输出
BBB