比较VTK数据类型和基本数据类型

Question

VTK has typedefs for basic types (float, int, double, etc.), and it assigns an integer per type. They are specified here .

The function GetDataType() , for example in vtkDataArray returns an integer that corresponds to one of the types. I would like to compare that integer with the basic data types (float, int, double).

Is there a way of doing so, easily ?

The usage I have of this is a template class which parameter T is a scalar. I want to check if the scalar point data of a dataset has the same data type as T.

For now, what I do, is a type size comparison :

vtkDataArray *scalars = image->GetPointData()->GetScalars();
if(scalars->GetDataTypeSize() != sizeof(T))
{
  std::cerr<<"Incompatible types"<<std::endl;
}

But obviously, float and int are both of size 4, so it doesn't really work.

Any ideas ?

Answer 1

After gathering information from a few places, I concluded there is no way to write it simply without creating the mapping myself between the two lists of types.

So, here is the most elegant way I found to do that :

I used the idea of norisknofun 's map, but I inverted it. I didn't use std::type_index() because it seems you can get the hash_code directly from the result of typeid() . I put this mapping in a function that transform basic type to VTK type, because it can serve other purposes than just comparison (see my other post ).

#include <vtkType.h>

int GetVTKType(std::size_t hash_code)
{
    static std::map<std::size_t, long> typeMap;
    if(typeMap.empty())
    {
        typeMap[typeid(void).hash_code()]               = VTK_VOID;
        typeMap[typeid(char).hash_code()]               = VTK_CHAR;
        typeMap[typeid(signed char).hash_code()]        = VTK_SIGNED_CHAR;
        typeMap[typeid(unsigned char).hash_code()]      = VTK_UNSIGNED_CHAR;
        typeMap[typeid(short).hash_code()]              = VTK_SHORT;
        typeMap[typeid(unsigned short).hash_code()]     = VTK_UNSIGNED_SHORT;
        typeMap[typeid(int).hash_code()]                = VTK_INT;
        typeMap[typeid(unsigned int).hash_code()]       = VTK_UNSIGNED_INT;
        typeMap[typeid(long).hash_code()]               = VTK_LONG;
        typeMap[typeid(unsigned long).hash_code()]      = VTK_UNSIGNED_LONG;
        typeMap[typeid(float).hash_code()]              = VTK_FLOAT;
        typeMap[typeid(double).hash_code()]             = VTK_DOUBLE;
        typeMap[typeid(std::string).hash_code()]        = VTK_STRING;
        typeMap[typeid(long long).hash_code()]          = VTK_LONG_LONG;
        typeMap[typeid(unsigned long long).hash_code()] = VTK_UNSIGNED_LONG_LONG;
        typeMap[typeid(int64_t).hash_code()]            = VTK___INT64;
        typeMap[typeid(uint64_t).hash_code()]           = VTK_UNSIGNED___INT64;
    }
    return typeMap[hash_code];
}

Therefore, to compare a vtk data type, and a basic type (my template parameter T), I do :

vtkDataArray *scalars = image->GetPointData()->GetScalars();
if(scalars->GetDataType() != GetVTKType(typeid(T).hash_code()))
{
  std::cerr<<"Incompatible types"<<std::endl;
}

Or if I want a nice comparison function as norisknofun did it, I can do :

template < class T > 
bool is_same(long vtkType)
{
  return vtkType != GetVTKType(typeid(T).hash_code())
}

// somewhere.cpp
if(!is_same<T>(scalars->GetDataType()))
{
  std::cerr<<"Incompatible types"<<std::endl;
}

Answer 2

I guess you have to elaborate your own mapping. Your compiler must be c++11 compliant with RTTI activated but now most of modern compilers support this feature.

I dont know what is the c++ equivalent of 'bit', 'id_type' and 'opaque' types...

#include <iostream>
#include <typeinfo>
#include <typeindex>
#include <cstdint>
#include <string>
#include <map>

// copy from vtk header, use #include <vtkType.h> instead
#define VTK_VOID            0
#define VTK_BIT             1
#define VTK_CHAR            2
#define VTK_SIGNED_CHAR    15
#define VTK_UNSIGNED_CHAR   3
#define VTK_SHORT           4
#define VTK_UNSIGNED_SHORT  5
#define VTK_INT             6
#define VTK_UNSIGNED_INT    7
#define VTK_LONG            8
#define VTK_UNSIGNED_LONG   9
#define VTK_FLOAT          10
#define VTK_DOUBLE         11
#define VTK_ID_TYPE        12
#define VTK_STRING         13
#define VTK_OPAQUE         14
#define VTK_LONG_LONG          16
#define VTK_UNSIGNED_LONG_LONG 17
#define VTK___INT64            18
#define VTK_UNSIGNED___INT64   19

// vtktypes
    typedef long vtktypes ;

    // standard c++ types
    typedef std::size_t   mytypes ;
    typedef std::map< vtktypes, mytypes> map_t;

template < class T > 
bool is_same(vtktypes x)
{
    static std::map< vtktypes, mytypes> _map;
    if(_map.empty())
    {
        _map[VTK_VOID           ]   = std::type_index(typeid(void)).hash_code();
        //_map[VTK_BIT              ]   = std::type_index(typeid(void)).hash_code();
        _map[VTK_CHAR           ]   = std::type_index(typeid(char)).hash_code();
        _map[VTK_SIGNED_CHAR    ]   = std::type_index(typeid(signed char)).hash_code();
        _map[VTK_UNSIGNED_CHAR  ]   = std::type_index(typeid(unsigned char)).hash_code();
        _map[VTK_SHORT          ]   = std::type_index(typeid(short)).hash_code();
        _map[VTK_UNSIGNED_SHORT ]   = std::type_index(typeid(unsigned short)).hash_code();
        _map[VTK_INT            ]   = std::type_index(typeid(int)).hash_code();
        _map[VTK_UNSIGNED_INT   ]   = std::type_index(typeid(unsigned int)).hash_code();
        _map[VTK_LONG           ]   = std::type_index(typeid(long)).hash_code();
        _map[VTK_UNSIGNED_LONG  ]   = std::type_index(typeid(unsigned long)).hash_code();
        _map[VTK_FLOAT          ]   = std::type_index(typeid(float)).hash_code();

        _map[VTK_DOUBLE         ]   = std::type_index(typeid(double)).hash_code();
        //_map[VTK_ID_TYPE          ]   = type_index(typeid()).hash_code();
        _map[VTK_STRING         ]   = std::type_index(typeid(std::string)).hash_code();
        //_map[VTK_OPAQUE           ]   = type_index(typeid(void)).hash_code();
        _map[VTK_LONG_LONG         ]= std::type_index(typeid(long long)).hash_code();
        _map[VTK_UNSIGNED_LONG_LONG]= std::type_index(typeid(unsigned long long)).hash_code();
        _map[VTK___INT64           ]= std::type_index(typeid(int64_t)).hash_code();
        _map[VTK_UNSIGNED___INT64  ]= std::type_index(typeid(uint64_t)).hash_code();
    }

    map_t::iterator it = _map.find(x);
    return (it != _map.end()) && it->second == std::type_index(typeid(T)).hash_code();
}

int main()
{
    std::cout << "is same ? " << is_same<char>(2) << std::endl ;
    std::cout << "is same ? " << is_same<std::string>(13) << std::endl ;    

    return 0;
}

In your case, you can use it like that :

vtkDataArray *scalars = image->GetPointData()->GetScalars();
if(!is_same<T>(scalars->GetDataTypeSize()))
{
  std::cerr<<"Incompatible types"<<std::endl;
}