我正在尝试在portaudio中创建多个流。 这就是打开流所需要的
PaError Pa_OpenDefaultStream( PaStream** stream,
int numInputChannels,
int numOutputChannels,
PaSampleFormat sampleFormat,
double sampleRate,
unsigned long framesPerBuffer,
PaStreamCallback *streamCallback,
void *userData );
这是PaStreamCallback函数。
typedef int PaStreamCallback(
const void *input, void *output,
unsigned long frameCount,
const PaStreamCallbackTimeInfo* timeInfo,
PaStreamCallbackFlags statusFlags,
void *userData );
当我尝试使用以下方法传递回调函数时,编译器不接受:
std::bind(&MyStreamClass::OutputRouting, this, std::placeholders::_1, std::placeholders::_2, std::placeholders::_3, std::placeholders::_4, std::placeholders::_5, std::placeholders::_6)
这是我得到的错误:
error: cannot convert 'std::_Bind_helper<false, int (MyStreamClass::*)(const void*, void*, long unsigned int, const PaStreamCallbackTimeInfo*, long unsigned int, void*), MyStreamClass*, const std::_Placeholder<1>&, const std::_Placeholder<2>&, const std::_Placeholder<3>&, const std::_Placeholder<4>&, const std::_Placeholder<5>&, const std::_Placeholder<6>&>::type' {aka 'std::_Bind<int (MyStreamClass::*(MyStreamClass*, std::_Placeholder<1>, std::_Placeholder<2>, std::_Placeholder<3>, std::_Placeholder<4>, std::_Placeholder<5>, std::_Placeholder<6>))(const void*, void*, long unsigned int, const PaStreamCallbackTimeInfo*, long unsigned int, void*)>'} to 'int (*)(const void*, void*, long unsigned int, const PaStreamCallbackTimeInfo*, PaStreamCallbackFlags, void*)' {aka 'int (*)(const void*, void*, long unsigned int, const PaStreamCallbackTimeInfo*, long unsigned int, void*)'}
Pa_OpenDefaultStream(&stream, 0, 0, paFloat32, 0, 0, std::bind(&MyStreamClass::OutputRouting, this, std::placeholders::_1, std::placeholders::_2, std::placeholders::_3, std::placeholders::_4, std::placeholders::_5, std::placeholders::_6), nullptr);
那么,有什么方法可以将我的成员函数作为参数传递?
答案 0 :(得分:2)
您的回调应类似于:
int MyCallback(
const void *input, void *output,
unsigned long frameCount,
const PaStreamCallbackTimeInfo* timeInfo,
PaStreamCallbackFlags statusFlags,
void *userData )
{
return reinterpret_cast<MyStreamClass*>(userData)->OutputRouting(input, output, frameCount, timeInfo, statusFlags);
}
答案 1 :(得分:2)
有两种方法可以执行此操作。您可以使用void* userData
参数从非成员(或静态)函数指向您的类,并从该函数访问您的类。或者,您可以使用该非成员(或静态)函数在对象上调用成员函数:
class MyClass
{
public:
void register_callback_here()
{
Pa_OpenDefaultStream(stream, 2, 2, PaSampleFormat::whatever, 44100,
1024, &MyClass::pa_callback_mapper, this); // PASS this!!!
}
private:
// The actual call back
int callback(
const void* input, void* output,
unsigned long frameCount,
const PaStreamCallbackTimeInfo* timeInfo,
PaStreamCallbackFlags statusFlags)
{
// actual callback here
return 0;
}
// a pass-through function that reinterprets the userData as the this pointer
// then cals the member function using this.
static int pa_callback_mapper(
const void* input, void* output,
unsigned long frameCount,
const PaStreamCallbackTimeInfo* timeInfo,
PaStreamCallbackFlags statusFlags,
void* userData)
{
if(auto self = reinterpret_cast<MyClass*>(userData))
return self->callback(input, output, frameCount, timeInfo, statusFlags);
return 0;
}
};
注册回叫时,您将this
作为userData
传递。回调在回调函数中将指针返回给您。您可以将其强制转换为您的类类型,然后通过它访问您的类,或将调用转发给成员函数(如本例所示)。