ITK  5.3.0
Insight Toolkit
SphinxExamples/src/Core/Common/ReturnObjectFromFunction/Code.cxx
/*=========================================================================
*
* Copyright NumFOCUS
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0.txt
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*=========================================================================*/
#include "itkImage.h"
namespace
{
using ImageType = itk::Image<unsigned char, 2>;
}
ImageType::Pointer
ReturnSmartPointer()
{
ImageType::Pointer image = ImageType::New();
itk::Index<2> corner = { { 0, 0 } };
itk::Size<2> size = { { 10, 10 } };
itk::ImageRegion<2> region(corner, size);
image->SetRegions(region);
image->Allocate();
return image;
}
ImageType *
ReturnPointer()
{
ImageType::Pointer image = ImageType::New();
itk::Index<2> corner = { { 0, 0 } };
itk::Size<2> size = { { 10, 10 } };
itk::ImageRegion<2> region(corner, size);
image->SetRegions(region);
image->Allocate();
return image;
}
int
main(int, char *[])
{
{
// This is how it should be done.
ImageType::Pointer smartPointer = ReturnSmartPointer();
std::cout << smartPointer->GetLargestPossibleRegion() << std::endl;
}
{
ImageType * pointer = ReturnPointer();
// This crashes the program because the smart pointer created in the function goes out of scope and gets deleted
// because it is returned as a normal pointer.
// std::cout << pointer->GetLargestPossibleRegion() << std::endl;
pointer = nullptr; // Here to silence warning
}
{
ImageType * pointer = ReturnSmartPointer();
// This crashes the program because though the function returned a ::Pointer, it was not stored
// anywhere so the reference count was not increased, so it got deleted.
// std::cout << pointer->GetLargestPossibleRegion() << std::endl;
pointer = nullptr; // Here to silence warning
}
{
// I thought this might also work, but it does not (crash).
// My reasoning was that even though you don't return a smart pointer, you assign the object to a smart
// pointer at return time, so it still has a reference count of 1.
// ImageType::Pointer smartPointer = ReturnPointer(); // this line causes a 'glibc error'
// std::cout << smartPointer->GetLargestPossibleRegion() << std::endl;
}
return 0;
}
itk::Index
Represent a n-dimensional index in a n-dimensional image.
Definition: itkIndex.h:67
itk::Size< 2 >
itk::ImageRegion
An image region represents a structured region of data.
Definition: itkImageRegion.h:69
itkImage.h
itk::Image
Templated n-dimensional image class.
Definition: itkImage.h:88