标准库定义的函数对象--接“将函数对象用于标准库算法”

标准库<functional>头文件中定义了一组类似于前边的GT_cls的函数对象。奇怪的是不需要include<functional>(mark)

有一元函数对象：一元减minus<Type>和逻辑非logical_not<Type>

其余都是二元函数对象

一个简单实例：

chap/functionObject.cpp

#include"head.h"

//#include<functional>

int main(){
	std::plus<int> intAdd;//function object that can add two int values.二元加
	std::negate<int> intNegate;//function object that can negate an int value/一元减
	
	//uses intAdd::operator(int, int) to add 10 and 20
	int sum = intAdd(10, 20);
	std::cout << sum << std::endl;
	//uses intNegate::operator(int) to generate -10 as second parameter
	//to intAdd::operator(int, int)
	sum = intAdd(10, intNegate(11));
	std::cout << sum << std::endl;
	
	
	//在算法中使用标准库函数对象
	std::vector<std::string> words(3, "fuck");
	words.push_back("killer");
	words.push_back("kiss");
	words.push_back("kif");
	words.push_back("asdad");
	
	for(std::vector<std::string>::iterator iter = words.begin(); iter != words.end(); iter++)
		std::cout << *iter << "\t";
	std::cout << std::endl << "After sort():" << std::endl;
	sort(words.begin(), words.end());//正常：operator< 按字符串（字母）升序
	for(std::vector<std::string>::iterator iter = words.begin(); iter != words.end(); iter++)
		std::cout << *iter << "\t";
	std::cout << std::endl << "After sort(b, e, greater<Type>):" << std::endl;
	//类似于GT_cls，不过后者是返回bool类型以供判断，
	//前者是要代替特定的（以operator<（也是返回bool估计，根据bool做排序）做升序排列的操作），达到以别的方式做升降序（严格来讲就是根据bool排序）排列
	sort(words.begin(), words.end(), std::greater<std::string>());//定制：greater<string> stands for operator<  按字符串（字母）降序
	for(std::vector<std::string>::iterator iter = words.begin(); iter != words.end(); iter++)
		std::cout << *iter << "\t";
}

function adapter 函数适配器

//函数对象的函数适配器
#include"head.h"

int main(){
    //绑定器binder:bind1st,bind2nd;绑定一个现成的实参到二元函数对象函数第一个或第二个参数，使之变成一元函数
    int a[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
    std::vector<int> vec(a, a + 10);
    std::cout << count_if(vec.begin(), vec.end(), std::bind2nd(std::less_equal<int>(), 7)) << std::endl;
    //less_equal<Type> 不支持std::string类型
    
    //求反器negator:not1,not2;将一元函数对象或二元函数对象的真值求反
    //求反与绑定的嵌套使用
    std::cout << count_if(vec.begin(), vec.end(), not1(std::bind2nd(std::less_equal<int>(), 7))) << std::endl;
    
}

pe14_37.cpp