1.函式指標

process(think); //函式think()的地址傳給process()
process(think()); //函式think()的返回值傳給process()

2.函式符

函式符是可以以函式方式與()結合使用的任意物件。這包括函式名、指向函式的指標和過載了()

例如：

class f_mod{
	public:
		f_mod(int d = 1) :dv(d){};
		bool operator()(int x){ return x%dv == 0; }

	private:
		int dv;
	};

f_mod obj(3); //f_mod.dv=3

bool is_div_by_3 = obj(7); //等價於obj.operator()(7)
 

名稱lambda來自lambda calculus(λ演算)，一種定義和應用函式的數學系統。這個系統讓您能夠使用匿名函式——即無需給函式命名。在C++11中，對於接受函式指標或函式符的函式，可以使用匿名函式定義(lambda)作為其引數。

例如：

bool f3(int i){ return i % 3 == 0; }

[](int x){ return x % 3 == 0; }

                      2)沒有宣告返回型別。返回型別相當於使用decltyp根據返回值推斷得到的，這裡為bool。

函式指標、函式符和lambda函式code:

#include"iostream"
#include"vector"
#include"algorithm"
#include"cmath"
#include"ctime"

using namespace std;

const long Size1 = 39L;
const long Size2 = 100 * Size1;
const long Size3 = 100 * Size2;

bool f3(int i){ return i % 3 == 0; }
bool f13(int i){ return i % 13 == 0; }

int main()
{
	vector<int> numbers(Size1);
	srand(time(0));
	generate(numbers.begin(), numbers.end(),rand);
//使用函式指標
	cout << "Sample size"<<Size1<< endl;
	int count3 = count_if(numbers.begin(), numbers.end(),f3);
	int count13 = count_if(numbers.begin(), numbers.end(), f13);
	cout << "Conut of numbers divisible by 3：" << count3 << endl;
	cout << "Conut of numbers divisible by 13：" << count13 << endl;
	//增加numbers的個數
	numbers.resize(Size2);
	generate(numbers.begin(), numbers.end(), rand);
	cout << "Sample size" << Size2 << endl;
//使用函式符
	class f_mod
	{
	public:
		f_mod(int d = 1) :dv(d){};
		bool operator()(int x){ return x%dv == 0; }

	private:
		int dv;
	};
	 count3 = count_if(numbers.begin(), numbers.end(), f_mod(3));
	 count13 = count_if(numbers.begin(), numbers.end(), f_mod(13));
	cout << "Conut of numbers divisible by 3：" << count3 << endl;
	cout << "Conut of numbers divisible by 13：" << count13 << endl;
	//增加numbers的個數
	numbers.resize(Size3);
	generate(numbers.begin(), numbers.end(), rand);
	cout << "Sample size" << Size3 << endl;
//使用lambdas表示式
	 count3 = count_if(numbers.begin(), numbers.end(), [](int x){ return x % 3 == 0; });
	 count13 = count_if(numbers.begin(), numbers.end(), [](int x){ return x % 13 == 0; });
	cout << "Conut of numbers divisible by 3：" << count3 << endl;
	cout << "Conut of numbers divisible by 13：" << count13 << endl;
	system("pause");
	return 0;
}