C++中的lambda表达式

2014-08-27

lambda是什么

许多语言支持匿名函数的概念。这些函数有函数体、但是没有函数名称。lambda隐式定义函数对象类并构造该类类型的函数对象。

示例

排序的例子

#include <algorithm>
#include <iostream>
#include <vector>   

using namespace std;    

void abssort(vector<float> &numbers) {
    std::sort(numbers.begin(), numbers.end(),
            [](float a, float b) {
                return std::abs(a) < std::abs(b);
            });
}   

int main(){
    vector<float> numbers = {1,-1, -0.3, -101.1, 99};
    abssort(numbers);
    for(auto x:numbers){
        cout <<x << " ";
    }
    cout<< endl;
}

运行结果：

-0.3 1 -1 99 -101.1

保持状态的例子

void lambda_even() {
vector<int> v;
for (int i = 0; i < 10; ++i) {
  v.push_back(i);
}

// Count the number of even numbers in the vector by 
// using the for_each function and a lambda.
int evenCount = 0;
for_each(v.begin(), v.end(),[&evenCount] (int n) {
   cout << n;
   if (n % 2 == 0) {
      cout << " is even " << endl;
      ++evenCount;
   } else {
      cout << " is odd " << endl;
   }
});  

// Print the count of even numbers to the console.
cout << "There are " << evenCount 
     << " even numbers in the vector." << endl;
}

运行结果：

0 is even 
1 is odd 
2 is even 
3 is odd 
4 is even 
5 is odd 
6 is even 
7 is odd 
8 is even 
9 is odd 
There are 5 even numbers in the vector.

其他示例

其他示例，可以看msdn的：demo

语法

语法，也参考msdn：lambda语法

小结