Intermediate C++ Game Programming Tutorial 16

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In the video we take a look at a couple of bangers from <algorithm>, and we learn what lambda functions are and how to use them.

Topics Covered

  • Algorithms std::sort and std::remove_if
  • Concepts (as in, type concepts like Comparable)
  • <functional> functors as predicates
  • Lambda functions


In the video Chili states that std::remove does not preserve the relative order of elements in the container, but this is fake news! Relative order is preserved: [1]

In the homework solution there is a part where Chili uses an iterator into a stringstream [2]. This code no longer works due to changes (improvements) to the Visual Studio compiler. Basically, you cannot pass a temporary stream into the iterator constructor. See this: [3]

Video Timestamp Index

Tutorial 16

  • Generic Algorithms: how Templates and Iterators make Algorithms independent of Data Types and Containers 0:17
  • The std::sort algorithm and its requirements 0:43
  • Sorting a (forward) list std::list, using its member function std::list::sort() 2:16
  • Introducing Concepts / named requirements of types (e.g., the Compare requirement of std::sort) 2:54
  • Modyfing sorting order by passing a comparison function object (functor) as a predicate, like so:
    std::sort(vec.begin(),vec.end(),std::greater<int>{}); 3:17
    Note: vec is a std::vector of integers
  • Sort custom types, example code for sorting a custom class object by creating a functor, called like so:
    std::sort(vecObj.begin(),vecObj.end(),Obj::YLess{}); 4:07
  • Removing items from a container, std::remove and std::remove_if 6:11
    • Create a functor as a unary predicate for the std::remove function to remove elements using a threshold variable 8:28
    • Use container member function erase() to correct the endpoint of the container after the remove operation 9:51
  • Introducing Lambda functions to replace custom functors 11:51
  • Using the Lambda capture to bring in variables into the Lambda function 13:34
    • Capture syntax explained: [var],[&var],[=],[&],[newvar=var+10],[this], capture multiple variables, mix&match capture modes
    • Stateful Lambdas; changing captured lambda variables using the mutable flag 15:59
  • Some anxiety-reducing consolation by Chili 16:40
  • Syntax for a callable Lambda function 17:03
    • Make it callable once: [...](...){...}(vec.front());, functor is destroyed immediately
    • Keep the functor using auto mylamb = [...](...){...};, which can be called by bool result = mylamb(vec.front());, or std::remove_if(...,...,mylamb);
  • The power of C++ is in its flexibility. Example code for converting a string to lowercase:
  • Homework assignment 18:39
  • Introducing the Algorithm STD Gems series that takes a deep dive into its functionality 19:20


Solve the problems in Source.cpp attached below using the <algorithm> library and other parts of the standard library as extensively as possible. As a bonus problem, implement the sprite drawing effect shown at the end of the video using a lambda function.

The homework solution video can be found here

Related Series

For an in-depth look into the <algorithm> library and beyond, check out STD Gems.


Algorithms Library

See also