diff options
| -rw-r--r-- | c++.html.markdown | 70 |
1 files changed, 70 insertions, 0 deletions
diff --git a/c++.html.markdown b/c++.html.markdown index f4aa2f5a..44cad665 100644 --- a/c++.html.markdown +++ b/c++.html.markdown @@ -820,6 +820,76 @@ std::map<Foo, int, compareFunction> fooMap; fooMap[Foo(1)] = 1; fooMap.find(Foo(1)); //true +/////////////////////////////////////// +// Lambda Expressions (C++11 and above) +/////////////////////////////////////// + +// lambdas are a convenient way of defining an anonymous function +// object right at the location where it is invoked or passed as +// an argument to a function. + +// For example, consider sorting a vector of pairs using the second +// value of the pair + +vector<pair<int, int> > tester; +tester.push_back(make_pair(3, 6)); +tester.push_back(make_pair(1, 9)); +tester.push_back(make_pair(5, 0)); + +// Pass a lambda expression as third argument to the sort function +// sort is from the <algorithm> header + +sort(tester.begin(), tester.end(), [](const pair<int, int>& lhs, const pair<int, int>& rhs) { + return lhs.second < rhs.second; + }); + +// Notice the syntax of the lambda expression, +// [] in the lambda is used to "capture" variables +// The "Capture List" defines what from the outside of the lambda should be available inside the function body and how. +// It can be either: +// 1. a value : [x] +// 2. a reference : [&x] +// 3. any variable currently in scope by reference [&] +// 4. same as 3, but by value [=] +// Example: + +vector<int> dog_ids; +// number_of_dogs = 3; +for(int i = 0; i < 3; i++) { + dog_ids.push_back(i); +} + +int weight[3] = {30, 50, 10}; + +// Say you want to sort dog_ids according to the dogs' weights +// So dog_ids should in the end become: [2, 0, 1] + +// Here's where lambda expressions come in handy + +sort(dog_ids.begin(), dog_ids.end(), [&weight](const int &lhs, const int &rhs) { + return weight[lhs] < weight[rhs]; + }); +// Note we captured "weight" by reference in the above example. +// More on Lambdas in C++ : http://stackoverflow.com/questions/7627098/what-is-a-lambda-expression-in-c11 + +/////////////////////////////// +// Range For (C++11 and above) +/////////////////////////////// + +// You can use a range for loop to iterate over a container +int arr[] = {1, 10, 3}; + +for(int elem: arr){ + cout << elem << endl; +} + +// You can use "auto" and not worry about the type of the elements of the container +// For example: + +for(auto elem: arr) { + // Do something with each element of arr +} + ///////////////////// // Fun stuff ///////////////////// |