Const Functions, like virtual void Function() const; - Epic Wiki
# Const Functions, like virtual void Function() const;
# Contents
# Overview
Const functions can be used to declare intent when writing a function and are also better for performance.
Research C++ const functions for more information on how this can lead to more efficient code.
Const functions are functions that are not allowed to modify any member variables of the class that they are part of.
# Overriding Const Functions
As you are overriding Epic's viritual functions you might encounter function syntax like this!
virtual int32 GetFlowerPetalCount() const;
Okay, maybe you're overriding a virtual function in one of my Flower Island plugins 😃
But anyway!
The point is that when you override const functions like this one, you have to do it like this
# .H
virtual int32 GetFlowerPetalCount() const OVERRIDE;
# .CPP
int32 AMyClass::GetFlowerPetalCount() const { return 7; }
# So What Are Const Functions For?
# Clarity
Use a const function any time you are accessing read-only data, or are doing complex analysis of that data, but not modifying the class's member variables.
# Protection
You can use const functions to protect member variables that you want users of your code to access, but not modify.
# FORCEINLINE Const Functions
FORCEINLINE allows you to declare a function entirely in the .h file and is great for code efficiency, as it means that a function is not added to the stack but is executed in Line.
FORCEINLINE + const is super amazing function efficiency and you will see it often in the UE4 C++ source!
//Member variable TArray<AStar*> Stars; //inline function that is const FORCEINLINE int32 GetStarCount() const { return Stars.Num(); } //inline function that is const FORCEINLINE FVector GetFirstStarPosition() const { if (Stars.Num() < 1 ) return FVector::ZeroVector; if (!Stars[0]) return FVector::ZeroVector; if (!Stars[0].IsValidLowLevel()) return FVector::ZeroVector; //~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ return Stars[0]->GetActorLocation(); } //inline function that cannot be const FORCEINLINE void RemoveLastStar() { if (Stars.Num() < 1 ) return; //this is a modification to the class member variable // so it cannot be const Stars.RemoveAt(Stars.Num() - 1); }
# Summary
Use const functions to:
declare that a function should never modify it's class member variables, for anyone who will be extending your viritual function,
and also as method of improving code performance!
Enjoy!
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