C++ lambda 表達式

lambda 表達式可理解爲匿名函數，或函數符，如函數指針。

bool f3(int x)
{
 return x % 3 == 0;
}
等效於 []（int x）{ return x % 3 == 0 }; 比較其形式，函數名被匿名了。

舉個栗子

#include <stdio.h>
#include <iostream>
#include <stdlib.h>
#include <math.h>
#include <algorithm>
#include <vector>
#include <ctime>
using namespace std;
bool f3(int x)
{
 return x % 3 == 0;
}
//[]（int x）{ return x % 3 == 0 };

#define N1 33
#define N2 N1*10
#define N3 N2*10
int main()
{
 class fmod
 {
 public: fmod(int d = 3) : dv(d) {};
   bool operator() (int x)
   {
    return x % dv == 0;
   }
 private: int dv;
   
 };
 srand(time(0));
 vector<int> Numbers(100);
 std::generate(Numbers.begin(), Numbers.end(), rand);
 cout << "Number of rand numbers divisible by 3 " << count_if(Numbers.begin(), Numbers.end(), [](int x) {return x % 3 == 0; }) << endl;
 Numbers.resize(N2);
 std::generate(Numbers.begin(), Numbers.end(), rand);
 cout << "Number of rand numbers by f3 " << count_if(Numbers.begin(), Numbers.end(), f3) << endl;
 
 Numbers.reserve(N3);
 std::generate(Numbers.begin(), Numbers.end(), rand);
 cout << "Number of rand numbers divisible by 33 " << count_if(Numbers.begin(), Numbers.end(), fmod(33)) << endl;
 getchar();
 return 0;
}