[vtkusers] vtk class error

[David Doria]

On Thu, Oct 7, 2010 at 4:42 PM, Jothy <jothybasu at gmail.com> wrote:

> Hi Guys,
>
> I am trying to create a c++ class to read a dicom image set. But,my app is
> crashing with out any errors during building.
>
> here is the header and source of that class, I am using Qt creator.
>
> Header:
>
> #ifndef MYDCMIMPORTER_H
>
> #define MYDCMIMPORTER_H
>
> #include<vtkImageData.h>
>
> #include<QString>
>
> class myDcmImporter
>
> {
>
> public:
>
>     myDcmImporter();
>
>     vtkImageData* imageData;
>
>     vtkImageData* readImage();
>
> };
>
> #endif // MYDCMIMPORTER_H
>
>
> Source:
> #include "mydcmimporter.h"
>
> #include<QFileDialog>
>
> #include<QString>
>
> #include<vtkDICOMImageReader.h>
>
> #include<vtkSmartPointer.h>
>
> #include<QDebug>
>
> myDcmImporter::myDcmImporter()
>
> {
>
> }
>
> vtkImageData* myDcmImporter::readImage()
>
> {
>
>     QString imageDirName=QFileDialog::getExistingDirectory();
>
>     vtkSmartPointer <vtkDICOMImageReader> reader=
>
>             vtkSmartPointer<vtkDICOMImageReader>::New();
>
>     reader->SetDirectoryName(imageDirName.toLatin1());
>
>     reader->Update();
>
>     this->imageData= reader->GetOutput();
>
> }
>
>
> App crashes only while executing
>
> myDcmImporter dcmImporter;
>
>     dcmImporter.readImage();
>
> //    vtkImageData *img=dcmImporter.imageData;
>
>     int dims[3];
>
>     dcmImporter.imageData->GetDimensions(dims);
>
> //    dcmImporter.imageData->GetDimensions(dims);
>
>     qDebug()<<dims[0]<<"running...";
>
>
> Since I am new to c++, could be a silly mistake somewhere.
>
> Thank you
>
> Jothy
>
>
This function is supposed to return a vtkImageData*, but there is no
'return' statement!

vtkImageData* myDcmImporter::readImage()
{
    QString imageDirName=QFileDialog::getExistingDirectory();
    vtkSmartPointer <vtkDICOMImageReader> reader=
            vtkSmartPointer<vtkDICOMImageReader>::New();
    reader->SetDirectoryName(imageDirName.toLatin1());
    reader->Update();
    this->imageData= reader->GetOutput();
}

However, I don't think this is the problem because you call the function
without asking for its return value anyway.

What may be happening is that the reader smart pointer is going out of
scope. I think you could fix this in two ways

1) Change the member
vtkImageData* imageData;
to
vtkSmartPointer<vtkImageData> imageData;

I'm not sure, but that might make the reader pointer hang around longer.

2) (this will definitely work)
Create the imageData object in the constructor:

myDcmImporter::myDcmImporter()

{

  this->imageData = vtkImageData::New();

}


Then instead of assigning the pointer:


    this->imageData= reader->GetOutput();


actually copy the output of the filter:

    this->imageData->ShallowCopy(reader->GetOutput());


Give those a shot and let us know if you have any luck.


David
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