Introduction to C + + lambda expressions

Lambda expression

The primary purpose of the C++11 standard lambda introduction is to:

A function-like expression can be used as a function parameter that accepts a function pointer or function, so a typical lambda expression is a test expression or a comparison expression that can be written as a statement, making Lambda simple and easy to understand.

1. A lambda expression has the following types:

[Capture List] (parameter list)->returntype{function body}

Capture list is a list of local function variables defined in a function that contains a lambda, return type, parameter list, and function list, respectively, representing return types, argument lists, and body of functions.

2. Lambda Capture and return

(1), Value capture

size_tv1=23;

Autof2=[v1]{return v1;}

v1=0;

Autoj=f ();//j=23

(2), reference capture

size_tv2=34;

Autof2=[&v2]{return v2;}

v1=0;

Autoj=f ();//j=0

(3), implicit capture

W=find_if (Q.begin (), Q.end (), [=] (conststring &s) {return s.size () >=sz;}) = Capture for value,& for reference

(4), variable lambda

If you want to change the captured variable, you must precede the parameter with mutable, as in the following example:

size_tv1=23;

AUTOF2=[V1] () Mutable{return ++v1;}

v1=0;

Autoj=f ();//j=23//j=24

size_tv2=34;

Autof2=[&v2]{return ++v2;}

v1=0;

Autoj=f ();//j=1

Capture List of lambda

[]-------An empty capture list, lambda cannot use the function variable in which it is located, and a lambda can only use it after capturing the variable;

[Names]--------names is a comma-separated list of names;

[&]----------An implicit capture list, using a reference capture method;

[=]-----------An implicit capture list, using the value capture method;

Use the sample code:

Use of/*LAMBDA expressions */#include <iostream> #include <vector> #include <cmath> #include <algorithm># Include<ctime>using namespace Std;void lambda () {vector<int> numbers (Size), Srand (Time (0)); Generate (Numbers.begin (), Numbers.end (), Rand);//Generate a random number and join the container cout<< "size=" <<numbers.size () << ' \ n ';//the size of the container int count3=count_if (Numbers.begin (), Numbers.end (), [] (int x) {return x%3==0;}); The/LAMBDA expression implements the number of computations divisible by 3 cout<< "count3=" <<count3<< ' \ n '; int Count13=0;for_each (Numbers.begin (), Numbers.end (), [&count13] (int x) {count13+=x%13==0;}); cout<< "count13=" <<count13<< ' \ n '; Count3=count13=0;for_each (Numbers.begin (), Numbers.end (), [ &] (int x) {count3+=x%3==0;count13==x%13==0;}); cout<< "count3=" <<count3<< ' \ n '; cout<< "count13=" <<count13<< ' \ n ';} int main () {lambda (); return 0;}

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Introduction to C + + lambda expressions