Lambda Function in C++

Introduction

Lambda functions are quite popular in .net world and with standardization in C++11, its get included in the language standard and available with VS2010. These are type of function which can be declared anonymously and without having name.

Using the code   

[1] (2) ->type {function body}(actual argument);

Here

Now let discuss it further with the example:-

Ex1 : Lambda function without parameter

This lambda function would return earth gravity as double type

double earthGravity = []()->double { return 9.81;}();

Ex2 : Lambda function with parameter

Say if you want to get area of rectangle by passing length and breath

int rectangleArea = [](int ilength,int iBreath)-> int
                    { return ilength*iBreath;}(10,20);

Here I create a lambda function with two parameter, return type int and passed the argument 10 and 20 and rectangleArea would contain the result 200,  once it's get executed

Ex3 : Lambda function with parent scope variable

Here I am creating two vector, first vector will contain the all the natural number from 1-10 and using lambda function we will add all the even number into the new vector which I going to pass by reference. I have explained the code in comments

#include <iostream>
#include <vector>

using namespace std;

int _tmain(int argc, _TCHAR* argv[])
{
	vector <int>vecInt;
	vector <int>evenNumberVec;

	//fill our main vector with dummy data
	for(int iCount =1;iCount<10;iCount++) 
          vecInt.push_back(iCount);

	//get all even number from vector using anonymous function
	bool rFlag =
	[vecInt](vector<int> &vecTmp)->bool{
		vector<int>::const_iterator it = vecInt.begin();
		while(it!=vecInt.end())
		{
			if((*it%2)==0)
				vecTmp.push_back(*it);
			it++;
		}
		return true;
	}(evenNumberVec);

	// print them
	for(int iCount =0;iCount <evenNumberVec.size();iCount++)
                std::cout<<evenNumberVec.at(iCount)<<std::endl;
	return 0;
}

Ex4 : Lambda function with parent scope variable (Pass By Reference)

bool rFlag =
    [&vecInt,&evenNumberVec]()->bool{
        vector<int>::const_iterator it = vecInt.begin();
        while(it!=vecInt.end())
        {
            if((*it%2)==0)
                evenNumberVec.push_back(*it);
            it++;
        }
        return true;
    }();

Points of Interest