func( )
到底是什么ret = func(x);
template<class F, class T>
T useF(F f, T x)
{
static int count = 0;
cout << "count:" << ++count << endl;
cout << "count:" << &count << endl;
return f(x);
}
double f(double i)
{
return i / 2;
}
struct Functor
{
double operator()(double d)
{
return d / 3;
}
};
int main()
{
// 函数指针
cout << useF(f, 11.11) << endl;
// 函数对象
cout << useF(Functor(), 11.11) << endl;
// lambda表达式
cout << useF([](double d)->double { return d / 4; }, 11.11) << endl;
return 0;
}
std::function在头文件<functional>
// 类模板原型如下
template <class T> function; // undefined
template <class Ret, class... Args>
class function<Ret(Args...)>;
模板参数说明:
Ret: 被调用函数的返回类型
Args…:被调用函数的形参
ret = func(x);(可能是函数名?函数指针?函数对象(仿函数对象)?也有可能是lamber表达式对象)
template<class F, class T>
T useF(F f, T x)
{
static int count = 0;
cout << "count:" << ++count << endl;
cout << "count:" << &count << endl;
return f(x);
}
double f(double i)
{
return i / 2;
}
struct Functor
{
double operator()(double d)
{
return d / 3;
}
};
int main()
{
// 函数指针
cout << useF(f, 11.11) << endl;
// 函数对象
cout << useF(Functor(), 11.11) << endl;
// lambda表达式
cout << useF([](double d)->double { return d / 4; }, 11.11) << endl;
// 可调用对象存储到容器中
//vector<>
// 包装器 -- 可调用对象的类型问题
//function<返回值类型(参数类型)>
function<double(double)> f1 = f;// 函数名
function<double(double)> f2 = [](double d)->double { return d / 4; };// 函数对象
function<double(double)> f3 = Functor();// lamber表达式
//vector<function<double(double)>> v = { f1, f2, f3 };//写法一
//我们 通过function语法即可成功把他们放到vector中
vector<function<double(double)>> v = { f, [](double d)->double { return d / 4; }, Functor() };//写法二
double n = 3.3;
for (auto f : v)
{
cout << f(n++) << endl;//遍历vector,每个元素是一个包装器
}
return 0;
}
rSub(10,5)
通过变换bind 函数包装器 中placeholders::_1, placeholders::_2
,可以实现10-5&5-10
double Plus(int a, int b, double rate)
{
return (a + b) * rate;
}
int main()
{
function<double(int, int)> Plus1 = bind(Plus, placeholders::_1, placeholders::_2, 4.0);
function<double(int, int)> Plus2 = bind(Plus, placeholders::_1, placeholders::_2, 4.2);
function<double(int, int)> Plus3 = bind(Plus, placeholders::_1, placeholders::_2, 4.4);
cout << Plus1(5, 3) << endl;
cout << Plus2(5, 3) << endl;
cout << Plus3(5, 3) << endl;
return 0;
}
double Plus(int a, double rate,int b)
{
return (a + b) * rate;
}
int main()
{
function<double(int, int)> Plus1 = bind(Plus, placeholders::_1, 4.0 placeholders::_2);
function<double(int, int)> Plus2 = bind(Plus, placeholders::_1, 4.2,placeholders::_2);
function<double(int, int)> Plus3 = bind(Plus, placeholders::_1,4.4 ,placeholders::_2);
cout << Plus1(5, 3) << endl;
cout << Plus2(5, 3) << endl;
cout << Plus3(5, 3) << endl;
return 0;
}
主要方法分为下面三种:
&SubType::sub
&SubType::sub
,法一:先实例化出一个类SubType st;
,取其地址&st
&SubType::sub
,法二:直接传入一个匿名对象SubType()
class SubType
{
public:
static int sub(int a, int b)
{
return a - b;
}
int ssub(int a, int b, int rate)
{
return (a - b) * rate;
}
};
int main()
{
//对于静态成员函数
function<double(int, int)> Sub1 = bind(&SubType::sub, placeholders::_1, placeholders::_2);
cout << Sub1(1, 2) << endl;
//对于非静态成员函数,法一
SubType st;
function<double(int, int)> Sub2 = bind(&SubType::ssub, &st, placeholders::_1, placeholders::_2, 3);
cout << Sub2(1, 2) << endl;
//对于非静态成员函数,法二
function<double(int, int)> Sub3 = bind(&SubType::ssub, SubType(), placeholders::_1, placeholders::_2, 3);
cout << Sub3(1, 2) << endl;
return 0;
}