[Insight-developers] Templates and preprocessor macros
Benoit Scherrer
benoitscherrer at gmail.com
Wed Jul 20 11:14:39 EDT 2011
Hi,
Wow thank you very much. I think that's a perfect way to do what i wanted to
do.
Thanks again!!
Benoit
On Wed, Jul 13, 2011 at 12:24 PM, Williams, Norman K <
norman-k-williams at uiowa.edu> wrote:
> I think what Benoit wants is to execute different processing steps based
> on ImageType::ImageDimension.
>
> What seems like you'd want -- specialization of template member function,
> isn't legal C++. And if partial specialization of non-class helper
> functions works, I haven't figured out the syntax recipe for it.
>
> Here, though is a mockup of how you could do it with member function
> overloads:
>
> /*
> * Demonstrate using template + overload pattern to
> * handle different ImageDimension cases differently
> */
> #include <iostream>
> #include <itkImage.h>
>
> template <typename TImage>
> class TestClass
> {
> public:
> typedef TImage ImageType;
> typedef typename ImageType::Pointer ImagePointer;
> void Execute();
> private:
> /** fallback case -- doesn't do anything */
> template <typename TImage2>
> ImagePointer _Execute(TImage2 *input);
> /** specifically handle 2D */
> ImagePointer _Execute(typename itk::Image<typename TImage::PixelType,2>
> *input);
> /** specifically handle 3D */
> ImagePointer _Execute(typename itk::Image<typename TImage::PixelType,3>
> *input);
> };
>
>
> /** ND case */
> template <class TImage>
> template <class TImage2>
> typename TestClass<TImage>::ImagePointer
> TestClass<TImage>
> ::_Execute(TImage2 *input)
> {
> std::cerr << "Unsupported Dimension" << std::endl;
> return input;
> }
>
> /** 2D Case */
> template <class TImage>
> typename TestClass<TImage>::ImagePointer
> TestClass<TImage>
> ::_Execute(typename itk::Image<typename TImage::PixelType,2> *input)
> {
> std::cerr << "2D" << std::endl;
> ImagePointer output;
> // do 2D processing
> return output;
> }
>
> /** 3D Case */
> template <class TImage>
> typename TImage::Pointer
> TestClass<TImage>
> ::_Execute(typename itk::Image<typename TImage::PixelType,3> *input)
> {
> std::cerr << "3D" << std::endl;
> ImagePointer output;
> // do 3D processing
> return output;
> }
>
> template <class TImage>
> void
> TestClass<TImage>
> ::Execute()
> {
> ImagePointer p;
> this->_Execute(p.GetPointer());
> }
>
> int main(int argc, char *argv[])
> {
> typedef itk::Image<unsigned char,4> Image4DType;
> typedef itk::Image<unsigned char,3> Image3DType;
> typedef itk::Image<unsigned char,2> Image2DType;
>
> TestClass<Image4DType> test4D;
> TestClass<Image3DType> test3D;
> TestClass<Image2DType> test2D;
> test4D.Execute();
> test3D.Execute();
> test2D.Execute();
> }
>
>
> On 7/12/11 8:48 PM, "Bradley Lowekamp" <blowekamp at mail.nih.gov> wrote:
>
> With C++0x there is the static_assert:
>
> http://en.wikipedia.org/wiki/C%2B%2B0x#Static_assertions
>
> Which is by far the easiest was to check what you are looking for, as it
> is just :
>
> static_assert( VImageDimension == 3 );
>
> *poof* compile time assertion. However, this is not supported by all
> compilers that ITK needs to support so we can't do that for the main code.
> But if it's just your own project you could use it.
>
> I would be in favor for adding a itkStaticAssert as a macro to ITKv4.
> But I am also a meta-programing wacko, so I may be alone. We could use the
> C++0x implementation if available or fall back to something else, or just do
> nothing.
>
> Brad
>
> On Jul 11, 2011, at 1:28 PM, Williams, Norman K wrote:
>
> The only way to solve this is with template metaprogramming. This makes
> for some extra work getting the syntax right, but you can write the code
> so that it only uses a filter on 3D.
> On the other hand, as one of the people who worked on OrientImageFilter
> back in the day, I don't think anyone should be using OrientImageFilter
> and it should be deprecated, because it destroys information. It only does
> the right thing if all of the direction cosines are aligned with one of
> the world coordinate axes.
> On 7/11/11 11:10 AM, "Benoit Scherrer" <benoitscherrer at gmail.com> wrote:
>
> Hi,
> Is there a way to use the C++ preprocessor macros that test the value of
> a template parameter?
> For example i want to do a generic image filter ( using itk::Image<type,
> VImageDimension> ) that
> will use itk::OrientImageFilter only for VImageDimension==3
> However, it seems that the preprocessor tool does not 'expand' the
> templates and
> just don't know when VImageDimension==3 or not.
> Is there any trick to do that, or is it a lost cause ?
> Thanks a lot!
> Benoit
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