C++ compiler waring C26409 – avoid calling new and delete

Here is my code that I’m getting (Warning C26409 Avoid calling new and delete explicitly, use std::make_unique instead (r.11).) after doing a Visual Studio 2019 Code Analysis:

#include <windows.h>
#include <strsafe.h>
int main()
{
    auto *sResult = new WCHAR[256];
    StringCchPrintfW(sResult, 256, L"this is a %s", L"test");
    delete[] sResult;
}

I was under the assumption to use new/delete instead of calloc/free, but now the compiler is telling me to use std::make_unique. I can’t find any examples on how I can change my code to be compliant.

So my questions are:

1. how do I change my code so it doens’t use new/delete

2. why should I not use new/delte vs std::make_unique?

>Solution :

The warning is somewhat confusing, because it assumes that you do need some direct memory allocation. If fact, you don’t:

#include <windows.h>
#include <strsafe.h>
#include <vector>
int main()
{
    std::vector<WCHAR> sResult(256);
    StringCchPrintfW(sResult.data(), sResult.size(), L"this is a %s", L"test");
}

or

int main()
{
    WCHAR sResult[256];
    StringCchPrintfW(sResult, 256, L"this is a %s", L"test");
}

The idea is to use static storage when you can (small data) to be more efficient (no OS memory call), and use std::vector when you must allocate because the size is either unknown at compile time or too big for the stack. The usage of std::make_unique is when you indeed need to call new directly or indirectly and have it auto-destruct later.

TL;DR: Read about modern C++ memory management.