an error about "amg.cpp"

[Tan.Q]

Hi， I study the Viennacl library. and when I bulid the example " amg.cpp " with opencl, it occured error .
at the begining of the code I write:

#define VIENNACL_WITH_OPENCL 1
#include "viennacl/ocl/platform.hpp"
#include "viennacl/ocl/backend.hpp"
#include "viennacl/context.hpp"
#include "viennacl/ocl/context.hpp"
#include "viennacl/forwards.h"

and the error occured in the sentence

viennacl::context ctx(viennacl::ocl::get_context(0));

the error description is
" Error 4 error C2664: 'viennacl::context::context(const viennacl::context &)' : cannot convert argument 1 from 'viennacl::ocl::context' to 'viennacl::memory_types' "
I wonder why about this.

AND I have another question: If I want compute on GPU , I must use " #define VIENNACL_WITH_OPENCL 1" ?
or this code has already compute with GPU defaultly. without write " #define VIENNACL_WITH_OPENCL 1 ".

Thank you very much !!!!!

[Karl Rupp]

Hi,
do you define VIENNACL_WITH_OPENCL before all of your ViennaCL-related includes? It looks like viennacl/context.hpp gets included indirectly at an earlier point. Generally I recommend to put the define as the first line in your source file.

As for your second question:
If you define VIENNACL_WITH_OPENCL, the code will run per default on the first device available on your system. To get an overview of the OpenCL devices on your system, build and run viennacl-info. The first device listed there is the default device (usually a GPU).

Best regards,
Karli