ITK/Examples/Utilities/ReturnObjectFromFunction

ReturnObjectFromFunction.cxx

<source lang="cpp">

1. include "itkImage.h"

namespace { typedef itk::Image<unsigned char, 2> ImageType; }

ImageType::Pointer ReturnSmartPointer() {

 ImageType::Pointer image = ImageType::New();
 itk::Index<2> corner = Template:0,0;
 itk::Size<2> size = Template: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 = Template:0,0;
 itk::Size<2> size = Template: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;
 }

 {
 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;
 }

 {
 // 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;

}

</source>

CMakeLists.txt

<syntaxhighlight lang="cmake"> cmake_minimum_required(VERSION 3.9.5)

project(ReturnObjectFromFunction)

find_package(ITK REQUIRED) include(${ITK_USE_FILE}) if (ITKVtkGlue_LOADED)

 find_package(VTK REQUIRED)
 include(${VTK_USE_FILE})

endif()

add_executable(ReturnObjectFromFunction MACOSX_BUNDLE ReturnObjectFromFunction.cxx)

if( "${ITK_VERSION_MAJOR}" LESS 4 )

 target_link_libraries(ReturnObjectFromFunction ITKReview ${ITK_LIBRARIES})

else( "${ITK_VERSION_MAJOR}" LESS 4 )

 target_link_libraries(ReturnObjectFromFunction ${ITK_LIBRARIES})

endif( "${ITK_VERSION_MAJOR}" LESS 4 )

</syntaxhighlight>

Download and Build ReturnObjectFromFunction

Click here to download ReturnObjectFromFunction and its CMakeLists.txt file. Once the tarball ReturnObjectFromFunction.tar has been downloaded and extracted,

cd ReturnObjectFromFunction/build

• If ITK is installed:

cmake ..

• If ITK is not installed but compiled on your system, you will need to specify the path to your ITK build:

cmake -DITK_DIR:PATH=/home/me/itk_build ..

Build the project:

make

and run it:

./ReturnObjectFromFunction

WINDOWS USERS PLEASE NOTE: Be sure to add the ITK bin directory to your path. This will resolve the ITK dll's at run time.

Building All of the Examples

Many of the examples in the ITK Wiki Examples Collection require VTK. You can build all of the the examples by following these instructions. If you are a new VTK user, you may want to try the Superbuild which will build a proper ITK and VTK.

ItkVtkGlue

ITK >= 4

For examples that use QuickView (which depends on VTK), you must have built ITK with Module_ITKVtkGlue=ON.

ITK < 4

Some of the ITK Examples require VTK to display the images. If you download the entire ITK Wiki Examples Collection, the ItkVtkGlue directory will be included and configured. If you wish to just build a few examples, then you will need to download ItkVtkGlue and build it. When you run cmake it will ask you to specify the location of the ItkVtkGlue binary directory.