How do I initialize a std::unique_ptr with a deleter in a constructor?

I'm trying to wrap a C library raw pointer in a std::unique_ptr and use the constructor with the Deleter to call the library free function. I have to do some setup in the constructor in order to setup the raw pointer so I can't construct the unique_ptr in the initializer list.

.h

class Resampler {    public:      Resampler(unsigned int baseSamplerate, unsigned int channels);      private:      std::unique_ptr<SwrContext, decltype(&swr_free)> context{nullptr, nullptr};  };  

.cpp

Resampler::Resampler(unsigned int baseSamplerate, unsigned int channels) : baseSamplerate(baseSamplerate), ratio(1.0), channels(channels) {        int64_t channelLayout;       ..        SwrContext *ctx = swr_alloc_set_opts(nullptr,                                           channelLayout,                                           AV_SAMPLE_FMT_FLTP,                                           baseSamplerate,                                           channelLayout,                                           AV_SAMPLE_FMT_FLTP,                                           baseSamplerate,                                           0,                                           nullptr);        context = std::unique_ptr<SwrContext, decltype(&swr_free)>(ctx, &swr_free);      setRatio(1.0);  }  

This doesn't produce an error in the IDE but the compiler complains:

> error: cannot initialize a parameter of type 'SwrContext **' with an  > lvalue of type 'std::__ndk1::unique_ptr<SwrContext, void  > (*)(SwrContext **)>::pointer' (aka 'SwrContext *')  

std::unique_ptr<SwrContext, decltype(&swr_free)> context{ nullptr };  

and

std::unique_ptr<SwrContext, decltype(&swr_free)> context{};  

are not valid constructors, and

std::unique_ptr<SwrContext, decltype(&swr_free)> context;  

produces

error: constructor for 'Resampler' must explicitly initialize the member 'context' which does not have a default constructor

so is there a way to do this or should I just make context a raw pointer and manually manage?

https://stackoverflow.com/questions/66056463/how-do-i-initialize-a-stdunique-ptr-with-a-deleter-in-a-constructor February 05, 2021 at 09:46AM