Unreal Engine C++: TArray doc sheet

Cheat sheet to unreal's TArray and equivalence with std::vector.

Basic

Advanced

Others

#include <algorithm>
std::vector<T> vec; 
typedef std::vector<T>::iterator it;
T item;
it = std::find(vec.begin(), vec.end(), item);

if( it != vec.end() ){
    //found
}

#include "Containers/Array.h"
TArray<T> array;
int32 index;
T item;
if( array.find(itm, index) )
{
    // found at 
    item == array[index];
}

Reduction

Find max

const TArray<float>& floatList;
float maxValue = 0.f;
if (const float* maxValuePtr = Algo::MaxElement(floatList))
    maxValue = FMath::Clamp(*maxValuePtr, 0.f, 1.f);

TArray<SomeStruct> myArray;
const SomeStruct* maxEltPtr = Algo::MaxElementBy(
    myArray, [](const SomeStruct& info) { return info.getMember(); }
);

float maxValue = (nullptr != maxEltPtr) ? *maxEltPtr : /*default value:*/ -1.0f;

TArray<float> myArray;
float maxValue = TNumericLimits<float>::Lowest();
for(int32 i = 0; i < myArray.Num(); ++i)
    maxValue = FMath::Max(myArray[i], maxValue);

if(myArray.Num() != 0){
    // Found
}

Code sample

{
    // []
    TArray<float> my_array;
    std::vector<float> my_vector;

    // ------------------------------------
    // Add/Push elements to the last entry
    // ------------------------------------
    
    // std::vector<>::push_back() <=> TArray<>::Add(), TArray<>::Push()
    
    // {1.0f}
    my_array.Add(1.0f); // Num=1; Max=4
    my_vector.push_back(1.0f); // size=1; capacity=1	

    // {1.0f, 2.0f}
    my_array.Add(2.0f); // Num=2
    my_vector.push_back(2.0f); // size=2

    // {1.0f, 2.0f, 3.0f}
    my_array.Push(3.0f); // Alias to my_array.Add(3.0f);
    my_vector.push_back(3.0f); 

    // std::vector<>::size() <=> TArray<>::Num()

    int32 size_a = my_array.Num(); // size_a = 3
    size_t size_v = my_vector.size(); // size_v = 3

    // std::vector<>::capacity() <=> TArray<>::Max()

    int32 unreal_max = my_array.Max(); // unreal_max = 4
    size_t std_capacity = my_vector.capacity(); // std_capacity = 3

    // ----------------------------
    // Get raw pointer to the array
    // ----------------------------
    
    // std::vector<>::data() <=> TArray<>::GetData()

    float* raw0 = my_array.GetData();
    float* raw1 = my_vector.data();		

    //-----------------
    // Get last element (index: 2, value: 3.0f)
    //-----------------

    // std::vector<>::back() <=> TArray<>::Last(), TArray<>::Top()

    float elt2 = my_array.Last(); // elt2 = 3.0f 
    elt2 = my_array.Top(); // elt2_ = 3.0f 
    float elt2_ = my_vector.back(); // elt2_ = 3.0f 

    //------------------
    // Get first element (index: 0, value: 1.0f)
    //------------------

    // std::vector<>::front() <=> TArray<>::[0], *TArray<>::begin()

    float elt0_ = my_vector.front(); // elt0_ = 1.0f 
    // no equivalent of the above
    float elt0 = my_array[0]; // elt0 = 1.0f 
    elt0 = *(my_array.begin()); // elt0 = 1.0f 
}

{
    // []
    TArray<float> my_array = {1.0f, 2.0f, 3.0f}; // Num=3
    std::vector<float> my_vector = { 1.0f, 2.0f, 3.0f }; // size=3; capacity=3

    //todo: my_array.Reset()
    my_array.Empty(); // Num=0; Max=0
    my_vector.clear(); // size=0; capacity=3

    bool s0 = my_array.IsEmpty(); // true
    bool s1 = my_vector.empty(); // true

}

/*
 Resizing and reserving memory:	
*/

struct Stuff {
    int a = -2;
};

{
    // Initialize and fill with default constructor T() of the container:

    std::vector<Stuff> my_vector(10);
    // note: TArray<float> my_array(10); not available in unreal
    // instead we use:
    TArray<Stuff> my_array; 
    // or perhaps alternatively: my_array.Init(Stuff(), 10); // ??
    my_array.SetNum(10);

    
    my_vector.reserve(20);		
    my_array.Reserve(20);

    // Resize and fill with default constructor T() of the container:		
    my_vector.resize(30); // Num=30;
    my_array.SetNum(30); // size=30	
}

/*
     Resizing and reserving memory:
     (unreal only features)
*/

{		
    // Specific to unreal				
    TArray<Stuff> my_array;
    my_array.AddDefaulted(2);     // {Stuff.a = -2, Stuff.a = -2 } same as std::vector<float> my_vector(2);
    my_array.AddUninitialized(2); // {Stuff.a = 'random value in memory', Stuff.a = 'rand val as well' }
    my_array.AddZeroed(2);        // {Stuff.a = 0, Stuff.a = 0 } sets memory to zero

    my_array.SetNumUninitialized(3);
    my_array.SetNumZeroed(4); // Zero out only *new* elements
}

Original Doc table of content:

• Creating and Filling an Array
• Iteration
• Sorting
• Queries
• Removal
• Operators
• Heap
• Slack
• Raw Memory
• Miscellaneous

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