# vtk class for wrapping/handling external command line program
**URL:** https://discourse.vtk.org/t/vtk-class-for-wrapping-handling-external-command-line-program/7403
**Category:** Support
**Created:** [December 15, 2021, 4:52am UTC](https://discourse.vtk.org/t/vtk-class-for-wrapping-handling-external-command-line-program/7403 "2021-12-15T04:52:37Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@Nicholas\_Yue](https://discourse.vtk.org/u/Nicholas_Yue)
#### Post date: [December 15, 2021, 4:52am UTC](https://discourse.vtk.org/t/vtk-class-for-wrapping-handling-external-command-line-program/7403/1 "2021-12-15T04:52:37Z")
I am looking to wrap some external commands in a C++ vtk class for developer’s convenience.
What class should I look into ?
Some of the external program are generator of information (source), some are filters and some are sink (e.g. send email/update status on web server via http call).
Cheers
---
### Author:  [@Nicholas\_Yue](https://discourse.vtk.org/u/Nicholas_Yue)
#### Post date: [December 16, 2021, 2:05am UTC](https://discourse.vtk.org/t/vtk-class-for-wrapping-handling-external-command-line-program/7403/2 "2021-12-16T02:05:40Z")
Answering my own question, I think the [vtkExecutableRunner](https://vtk.org/doc/nightly/html//classvtkExecutableRunner.html) is what I will start looking into.
It looks promising.
Cheers
---
### Author:  [@mwestphal](https://discourse.vtk.org/u/mwestphal)
#### Post date: [December 16, 2021, 9:00am UTC](https://discourse.vtk.org/t/vtk-class-for-wrapping-handling-external-command-line-program/7403/3 "2021-12-16T09:00:24Z")
FYI @Timothee_Chabat 🙂
---
### Author:  [@Timothee\_Chabat](https://discourse.vtk.org/u/Timothee_Chabat)
#### Post date: [December 16, 2021, 9:12am UTC](https://discourse.vtk.org/t/vtk-class-for-wrapping-handling-external-command-line-program/7403/4 "2021-12-16T09:12:31Z")
It was indeed created for that 🙂 just for your information @Nicholas_Yue vtkExecutableRunner is not an actual filter (ie it does not inherit `vtkAlgorithm`) so you will not be able to use it in a pipeline as is, but you can always create your own filters that wraps the class
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### Author:  [@Nicholas\_Yue](https://discourse.vtk.org/u/Nicholas_Yue)
#### Post date: [December 16, 2021, 5:18pm UTC](https://discourse.vtk.org/t/vtk-class-for-wrapping-handling-external-command-line-program/7403/5 "2021-12-16T17:18:46Z")
@Timothee_Chabat just clarifying that I should aim towards something like MyRunnerSI rather than MyRunnerMI
```auto
class MyRunnerSI : public vtkAlgorithm {
public:
void Execute(const char* command_string) {
vtkNew runner;
runner->SetCommand(command_string);
}
}
```
```auto
class MyRunnerMI : public vtkAlgorithm, public vtkExecutableRunner {
}
```
---
### Author:  [@Nicholas\_Yue](https://discourse.vtk.org/u/Nicholas_Yue)
#### Post date: [December 16, 2021, 9:16pm UTC](https://discourse.vtk.org/t/vtk-class-for-wrapping-handling-external-command-line-program/7403/6 "2021-12-16T21:16:51Z")
@Timothee_Chabat
Where would be the most appropriate place the call runner-\>Execute() within the vtkAlgorithm ? I think it should be ProcessRequest()
Here is my initial attempt base on my reading of vtkPolyDataAlgorithm class
```auto
#include "vtkRunnerFilter.h"
#include
#include
#include
#include
#include
#include
vtkStandardNewMacro(vtkRunnerFilter);
//------------------------------------------------------------------------------
vtkRunnerFilter::vtkRunnerFilter()
{
// by default assume filters have one input and one output
// subclasses that deviate should modify this setting
this->SetNumberOfInputPorts(1);
this->SetNumberOfOutputPorts(1);
_runnerPtr = vtkSmartPointer::New();
}
//------------------------------------------------------------------------------
vtkRunnerFilter::~vtkRunnerFilter() = default;
//------------------------------------------------------------------------------
void vtkRunnerFilter::PrintSelf(ostream& os, vtkIndent indent)
{
this->Superclass::PrintSelf(os, indent);
}
//------------------------------------------------------------------------------
vtkDataObject* vtkRunnerFilter::GetOutput()
{
return this->GetOutput(0);
}
//------------------------------------------------------------------------------
vtkDataObject* vtkRunnerFilter::GetOutput(int port)
{
return this->GetOutputDataObject(port);
}
//------------------------------------------------------------------------------
void vtkRunnerFilter::SetOutput(vtkDataObject* d)
{
this->GetExecutive()->SetOutputData(0, d);
}
//------------------------------------------------------------------------------
vtkDataObject* vtkRunnerFilter::GetInput()
{
return this->GetInput(0);
}
//------------------------------------------------------------------------------
vtkDataObject* vtkRunnerFilter::GetInput(int port)
{
return this->GetExecutive()->GetInputData(port, 0);
}
//------------------------------------------------------------------------------
vtkTypeBool vtkRunnerFilter::ProcessRequest(
vtkInformation* request, vtkInformationVector** inputVector, vtkInformationVector* outputVector)
{
// generate the data
if (request->Has(vtkDemandDrivenPipeline::REQUEST_DATA()))
{
return this->RequestData(request, inputVector, outputVector);
}
if (request->Has(vtkStreamingDemandDrivenPipeline::REQUEST_UPDATE_EXTENT()))
{
return this->RequestUpdateExtent(request, inputVector, outputVector);
}
// execute information
if (request->Has(vtkDemandDrivenPipeline::REQUEST_INFORMATION()))
{
return this->RequestInformation(request, inputVector, outputVector);
}
_runnerPtr->Execute();
return this->Superclass::ProcessRequest(request, inputVector, outputVector);
}
//------------------------------------------------------------------------------
int vtkRunnerFilter::FillOutputPortInformation(int vtkNotUsed(port), vtkInformation* info)
{
// now add our info
info->Set(vtkDataObject::DATA_TYPE_NAME(), "vtkExecutableRunner");
return 1;
}
//------------------------------------------------------------------------------
int vtkRunnerFilter::FillInputPortInformation(int vtkNotUsed(port), vtkInformation* info)
{
info->Set(vtkAlgorithm::INPUT_REQUIRED_DATA_TYPE(), "vtkExecutableRunner");
return 1;
}
//------------------------------------------------------------------------------
int vtkRunnerFilter::RequestInformation(vtkInformation* vtkNotUsed(request),
vtkInformationVector** vtkNotUsed(inputVector), vtkInformationVector* vtkNotUsed(outputVector))
{
// do nothing let subclasses handle it
return 1;
}
//------------------------------------------------------------------------------
int vtkRunnerFilter::RequestUpdateExtent(vtkInformation* vtkNotUsed(request),
vtkInformationVector** inputVector, vtkInformationVector* vtkNotUsed(outputVector))
{
int numInputPorts = this->GetNumberOfInputPorts();
for (int i = 0; i < numInputPorts; i++)
{
int numInputConnections = this->GetNumberOfInputConnections(i);
for (int j = 0; j < numInputConnections; j++)
{
vtkInformation* inputInfo = inputVector[i]->GetInformationObject(j);
inputInfo->Set(vtkStreamingDemandDrivenPipeline::EXACT_EXTENT(), 1);
}
}
return 1;
}
//------------------------------------------------------------------------------
// This is the superclasses style of Execute method. Convert it into
// an imaging style Execute method.
int vtkRunnerFilter::RequestData(vtkInformation* vtkNotUsed(request),
vtkInformationVector** vtkNotUsed(inputVector), vtkInformationVector* vtkNotUsed(outputVector))
{
return 1;
}
//------------------------------------------------------------------------------
void vtkRunnerFilter::SetInputData(vtkDataObject* input)
{
this->SetInputData(0, input);
}
//------------------------------------------------------------------------------
void vtkRunnerFilter::SetInputData(int index, vtkDataObject* input)
{
this->SetInputDataInternal(index, input);
}
//------------------------------------------------------------------------------
void vtkRunnerFilter::AddInputData(vtkDataObject* input)
{
this->AddInputData(0, input);
}
//------------------------------------------------------------------------------
void vtkRunnerFilter::AddInputData(int index, vtkDataObject* input)
{
this->AddInputDataInternal(index, input);
}
```
---
### Author:  [@Timothee\_Chabat](https://discourse.vtk.org/u/Timothee_Chabat)
#### Post date: [December 17, 2021, 8:16am UTC](https://discourse.vtk.org/t/vtk-class-for-wrapping-handling-external-command-line-program/7403/7 "2021-12-17T08:16:27Z")
Usually filters are doing the actual work when a REQUEST\_DATA request is given so I would put the Execute code in RequestData. Also I don’t think you need to handle REQUEST\_DATA\_EXTENT or REQUEST\_INFORMATION based on what you said, but you know better than me.
If you’re not sure what they are for and their order of executions I recommand you to read the 3 parts of the blog about the VTK pipeline, especially part 2 and 3 (see first part here [https://www.kitware.com/a-vtk-pipeline-primer-part-1](https://www.kitware.com/a-vtk-pipeline-primer-part-1))