vtkDataArrayIteratorMacro Class Reference

A macro for obtaining iterators to vtkDataArray data when the array implementation and type are unknown. More...

#include <vtkDataArrayIteratorMacro.h>

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Detailed Description

A macro for obtaining iterators to vtkDataArray data when the array implementation and type are unknown.

See vtkTemplateMacro. This macro is similar, but defines several additional typedefs and variables for safely iterating through data in a vtkAbstractArray container:

• vtkDAValueType is typedef'd to the array's element value type.
• vtkDAContainerType is typedef'd to the most derived class of vtkAbstractArray for which a suitable iterator has been found.
• vtkDAIteratorType is typedef'd to the most suitable iterator type found.
• vtkDABegin is an object of vtkDAIteratorType that points to the first component of the first tuple in the array.
• vtkDAEnd is an object of vtkDAIteratorType that points to the element after the last component of the last tuple in the array. The primary advantage to using this macro is that arrays with non-standard memory layouts will be safely handled, and dangerous calls to GetVoidPointer are avoided. For arrays with > 1 component, the iterator will proceed through all components of a tuple before moving on to the next tuple. This matches the memory layout of the standard vtkDataArray subclasses such as vtkFloatArray.

For the standard vtkDataArray implementations (which are subclasses of vtkDataArrayTemplate), the iterators will simply be pointers to the raw memory of the array. This allows very fast iteration when possible, and permits compiler optimizations in the standard template library to occur (such as reducing std::copy to memmove).

For arrays that are subclasses of vtkTypedDataArray (but not vtkDataArrayTemplate), a vtkTypedDataArrayIterator is used. Such iterators safely traverse the array using API calls and have pointer-like semantics, but add about a 35% performance overhead compared with iterating over the raw memory (measured by summing a vtkFloatArray containing 10M values on GCC 4.8.1 with -O3 optimization using both iterator types -- see TestDataArrayIterators).

For arrays that are not subclasses of vtkTypedDataArray, there is no reliably safe way to iterate over the array elements. In such cases, this macro performs the legacy behavior of casting vtkAbstractArray::GetVoidPointer(...) to vtkDAValueType* to create the iterators.

To use this macro, create a templated worker function:

template <class iterator>=""> void myFunc(Iterator begin, Iterator end, ...) {...}

and then call the vtkDataArrayIteratorMacro inside of a switch statement using the above objects and typedefs as needed:

vtkAbstractArray *someArray = ...; switch (someArray->GetDataType()) { vtkDataArrayIteratorMacro(someArray, myFunc(vtkDABegin, vtkDAEnd, ...)); }

See also:

vtkTemplateMacro vtkTypedDataArrayIterator

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The documentation for this class was generated from the following file:

• dox/Common/Core/vtkDataArrayIteratorMacro.h