Can't convert a function with const parameter to a function pointer?

Question

Even if you explicitly indicate that the parameter in the function pointer is const, it does not seem to be able to convert the function to this type:

#include <iostream> template <typename T> class Image{}; template <typename TPixel> static void FillImage(const Image<TPixel>* const image){} //FillImage(Image<TPixel>* const image){} // Replacing the above line with this one compiles fine int main() { typedef Image<float> ImageType; ImageType* image = new ImageType; void (*autoFunctionPointer)(const decltype(image)) = FillImage; autoFunctionPointer(image); } 

Can someone explain how to get this to do this conversion?

Answer 1

The pointer refers to const .

So const decltype(image) equivalent to ImageType* const , not const ImageType*

If you change image to

 const ImageType* image = new ImageType; 

The first version of FillImage() works as expected.

To get const ImageType* , you can use std :: remove_pointer

 #include <type_traits> ... void (*autoFunctionPointer)(const std::remove_pointer<decltype(image)>::type *) = FillImage; 

Answer 2

FillImage is a template, not a function. Try the FillImage<float> option.