CODEWITHSUNDEEP
c++winapistlsmart-pointers
Arush Agarampur
Arush Agarampur

Reputation: 1420

How to use a custom deleter using WinAPI with std::make_unique?

So I'm just experimenting with smart pointers and how I can manage Win32 HANDLE objects with them, so I wanted to test out this simple code I wrote.

It's supposed to provide a custom deleter for std::unique_ptr to use when the smart pointer goes outta scope.

template <typename Function>
class PtrDeleter
{
    Function _Closer;
public:
    void operator()(void* memBlock) const
    {
        _Closer(memBlock);
    }
};

//The std::make_unique is the one causing the problem...
std::unique_ptr<void*, PtrDeleter<decltype(CloseHandle)>> ptr = std::make_unique<void*>(OpenThread(...));

The reason I'm using a template for the Function parameter is because I'll be using other functions with CloseHandle, like CoTaskMemFree.

cannot convert from std::unique_ptr<void *,std::default_delete<_Ty>>' to 'std::unique_ptr<void *,PtrDeleter<BOOL (HANDLE)>>

This is what the compiler is outputting. Why is it still trying to use std::default_delete with std::make_unique?

Upvotes: 0

Views: 487

Answers (2)

김선달
김선달

Reputation: 1562

std::make_unique cannot make std::unique_ptr with a custom deleter. You have to manually call its constructor.

std::unique_ptr<void*, PtrDeleter<decltype(&CloseHandle)>> ptr{nullptr, CloseHandle}

In your case, it can be simplified to

std::unique_ptr<void*,decltype(&CloseHandle)> ptr{nullptr, CloseHandle}

No need to make a functor.

Upvotes: 3

rafix07
rafix07

Reputation: 20918

make_unique returns unique_ptr with defaulted deleter.

To provide your custom version you have to call unique_ptr(Pointer,Deleter) version of unique_ptr ctor:

template <typename Function>
class PtrDeleter {
    Function _Closer;
public:
    void operator()(void* memBlock) const {
        _Closer(memBlock);
    }
};

int main() {
    PtrDeleter<decltype(&CloseHandle)> deleter;
    void* openThread = OpenThread(0,false,0);
    std::unique_ptr<void, decltype(deleter)> ptr(openThread,deleter);
}

Demo

Upvotes: 4

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