How to concatenate two TStringDynArray?

Question

Is there a way to concatenate the content of one TStringDynArray to another TStringDynArray?

//First TStringDynArray
Item1
Item2
Item3

//Second TStringDynArray
ItemA
ItemB
ItemC

//Result after concatenate
Item1
Item2
Item3
ItemA
ItemB
ItemC

Answer 1

Not directly, as System::DynamicArray does not provide concatenation features in C++. So you would need to create a 3rd TStringDynArray, size it to the sum of the sizes of the 2 arrays, and individually copy each String from the 2 arrays into the 3rd array (String is reference-counted, so you can't just copy bytes with memcpy() or equivalent, like you can with arrays of trivial types), eg:

TStringDynArray Arr1;
// fill Arr1 as needed...

TStringDynArray Arr2;
// fill Arr2 as needed...

TStringDynArray MergedArr;
MergedArr.Length = Arr1.Length + Arr2.Length;
int idx = 0;

for(int i = 0; i < Arr1.Length; ++i) {
    MergedArr[idx++] = Arr1[i];
}

for(int i = 0; i < Arr2.Length; ++i) {
    MergedArr[idx++] = Arr2[i];
}

// use MergedArr as needed...

Alternatively (C++Builder 10.1 Berlin and later):

#include <algorithm>

TStringDynArray Arr1;
// fill Arr1 as needed...

TStringDynArray Arr2;
// fill Arr2 as needed...

TStringDynArray MergedArr;
MergedArr.Length = Arr1.Length + Arr2.Length;
std::copy(Arr1.begin(), Arr1.end(), MergedArr.begin());
std::copy(Arr2.begin(), Arr2.end(), MergedArr.begin() + Arr1.Length);

// use MergedArr as needed...

In the Clang-based compilers, you can take this a step further by using some variadic template functions to help you concatenate as many input TStringDynArray arrays as you want, eg:

#include <algorithm>

int ArrLength()
{
    return 0;
}

template<typename... Ts>
int ArrLength(TStringDynArray &arr, Ts&... others)
{
    return arr.Length + ArrLength(others...);
}

void ArrCopy(TStringDynArray::iterator dst)
{
}

template<typename... Ts>
void ArrCopy(TStringDynArray::iterator dst, TStringDynArray &arr, Ts&... others)
{
    std::copy(arr.begin(), arr.end(), dst);
    ArrCopy(dst + arr.Length, others...);
}

template<typename... Ts>
TStringDynArray ArrMerge(TStringDynArray &arr, Ts&... others)
{
    TStringDynArray res;
    res.Length = ArrLength(arr, others...);
    ArrCopy(res.begin(), arr, others...);
    return res;
}

...

TStringDynArray Arr1;
// fill Arr1 as needed...

TStringDynArray Arr2;
// fill Arr2 as needed...

TStringDynArray MergedArr = ArrMerge(Arr1, Arr2/*, Arr3, Arr4, ...*/);
// use MergedArr as needed...