29.03.2016, 20:48, Even Rouault kirjoitti:
Le mardi 29 mars 2016 17:35:26, Ari Jolma a écrit :
I want to write template functions like this:
template<typename cell_type>
void map(GDALRasterBand *b, mapper<cell_type> *mapper) {
...
This function would map the cell values of a band to new ones using some
logic that is coded within the mapper object (and the logic depends on
the cell_type).
I would like to catch errors which are due to mismatch between the band
data type and the template cell_type. So far I've discovered this:
band_wrapper band = band_initialize(b);
if (band.info.size_of_data_type != sizeof(cell_type))
goto fail_because_of_data_type_mismatch;
but it is not bullet proof since data types can have an equal size but
be different. The band_initialize contains a switch statement, which
sets the info element of the band wrapper.
Are there other ways to solve this problem? I could build long switch
statements but it is not very appealing. And it gets messy when there is
more than one band.
Perhaps by using C++ traits like this :
Indeed. Thanks!
Ari
#include <gdal.h>
template <typename T> struct GetGDALDataTypeTraits
{
static const GDALDataType datatype;
};
template<> struct GetGDALDataTypeTraits<unsigned char>
{
static const GDALDataType datatype = GDT_Byte;
};
template<> struct GetGDALDataTypeTraits<unsigned short>
{
static const GDALDataType datatype = GDT_UInt16;
};
template <typename T> static GDALDataType GetGDALDataType()
{
return GetGDALDataTypeTraits<T>::datatype;
}
#include <iostream>
int main(int argc, char* argv[])
{
std::cout << "type unsigned char: " << GetGDALDataType<unsigned char>() <<
std::endl;
std::cout << "type unsigned short: " << GetGDALDataType<unsigned short>() <<
std::endl;
// Link time error
//std::cout << "type double: " << GetGDALDataType<double>() << std::endl;
return 0;
}
Ari
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