The road to learning C++ primer-(Chapter 16 Function Objects)

The concept of function symbols :

• A generator is a function symbol that can be called without parameters
• Unary function is a function symbol that can be called with one parameter
• The second hospital function uses two parameters to call the function symbol
• The unary function operator that returns a bool value is a predicate
• The binary function operator that returns the bool value is a binary predicate

 Use bind1st or bind2nd function to convert one or two parameters into a single parameter function symbol

 1. The use of transform ()

 

#include <iostream>
#include <iterator>
#include <algorithm>
#include <vector>
#include <cmath>
#include <functional> /*定义了多个模板类函数对象*/
double mean(double x, double y)
{
	return x + y;
}
int main()
{
	using namespace std;
	const int LIM = 5;
	double arr1[LIM] = { 36,39,42,45,48 };
	vector<double>ar8(arr1, arr1 + LIM);
	ostream_iterator<double, char>out(cout, " ");
	vector<double>a = { 33,69,18,38,96 };
	transform(ar8.begin(), ar8.end(), a.begin(),out, mean); /*这时候ar8的区间长度必须与a的长度一致*/
	cout << endl;
	plus<double>add;/*头文件functional定义的 来完成常规相加运算*/
	
	transform(ar8.begin(), ar8.end(), a.begin(), out, add);
	cout << endl;
	transform(ar8.begin(), ar8.end(), out, bind1st(multiplies<double>(), 2.5));/*1st只是将第一个参数是常数赋值，第二个接受一个*/


	system("pause");
	return 0;
}