STL算法设计理念 - 预定义函数对象

预定义函数对象基本概念：标准模板库STL提前定义了很多预定义函数对象

1）使用预定义函数对象：

#include <iostream>#include <cstdio>#include <algorithm>#include <string>#include <vector>#include <functional>using namespace std;// plus，预定义好的函数对象，能实现不同类型数据的 + 运算// 实现了数据类型和算法的分离，通过函数对象技术实现的void play01(){/* plus函数对象原型template<class _Ty = void>struct plus: public binary_function < _Ty, _Ty, _Ty >{// functor for operator+_Ty operator()(const _Ty& _Left, const _Ty& _Right) const{// apply operator+ to operandsreturn (_Left + _Right);}};*/plus<int> intAdd; // 预定义函数对象int x = 10;int y = 20;int z = intAdd(x, y); // x + y;cout << "z: " << z << endl;// z : 30plus<string> stringAdd;string s1 = "lucifer";string s2 = "zhang";string s3 = stringAdd(s1, s2);cout << "s3: " << s3 << endl;// s3: luciferzhang}void play02(){vector<string> v;v.push_back("lucifer");v.push_back("zhang");v.push_back("yao");v.push_back("qi");/*template<class _Ty = void>struct greater: public binary_function < _Ty, _Ty, bool >{// functor for operator>bool operator()(const _Ty& _Left, const _Ty& _Right) const{// apply operator> to operandsreturn (_Left > _Right);}};*///缺省情况下，sort()用底层元素类型的小于操作符以升序排列容器的元素。//为了降序，可以传递预定义的类模板greater,它调用底层元素类型的大于操作符：sort(v.begin(), v.end(), greater<string>()); // 从大到小排序for (vector<string>::iterator it = v.begin(); it != v.end(); ++it) {cout << *it << ' ';}cout << endl;// zhang yao qi luciferstring sl = "lucifer";int num = count_if(v.begin(), v.end(), bind2nd(equal_to<string>(), sl));cout << "count of 'lucifer': " << num << endl;// count of 'lucifer': 1}int main(){play01();play02();return 0;}

2）算术函数对象
预定义的函数对象支持加、减、乘、除、求余和取反。调用的操作符是与type相关联的实例
加法：plus<Types>
plus<string> stringAdd;
sres = stringAdd(sva1,sva2);
减法：minus<Types>
乘法：multiplies<Types>
除法divides<Tpye>
求余：modulus<Tpye>
取反：negate<Type>
negate<int> intNegate;
ires = intNegate(ires);
Ires= UnaryFunc(negate<int>(),Ival1);

3）关系函数对象
等于equal_to<Tpye>
equal_to<string> stringEqual;
sres = stringEqual(sval1,sval2);
不等于not_equal_to<Type>
大于 greater<Type>
大于等于greater_equal<Type>
小于 less<Type>
小于等于less_equal<Type>

4）逻辑函数对象
逻辑与 logical_and<Type>
logical_and<int> indAnd;
ires = intAnd(ival1,ival2);
dres=BinaryFunc( logical_and<double>(),dval1,dval2);
逻辑或logical_or<Type>
逻辑非logical_not<Type>
logical_not<int> IntNot;
Ires = IntNot(ival1);
Dres=UnaryFunc( logical_not<double>,dval1);