Question

I’ve written an OpenCL kernel in a .cl file. It attempts to #include several headers.

Its compilation fails, since the included header files are “not found”.
I am aware that clBuildProgram can take the -I dir option, which adds the directory dir to the list of directories to be searched for the header files.

In the khronus site forum this post http://www.khronos.org/message_boards/viewtopic.php?f=37&t=2535 talks about the issue.

They propose to use clCreateProgramWithSource which specifies all sources (including .h files).

I have a questions regarding this issue:

1. Which option is better? (clBuildProgram vs. clCreateProgramWithSource, as described above)
2. If I use clCreateProgramWithSource how does the compiler know what to include? I mean, which source stands for which included file name?
3. If I use clBuildProgram and there are several directories with include files, how do I specify them?

Answer 1

OpenCL requires you use clCreateProgramWithSource() followed by clBuildProgram().

ClCreateProgramWithSource() creates and returns a cl_program object.

That cl_program object is input into clBuildProgram().

clBuildProgram() allows you to specify compiler options which include the include file
directories. In your case, for header file includes, it will be something like the string:

-I myincludedir1 -I myincludedir2  ...

The compiler used is the internal OpenCL compiler in the OpenCL SDK you are using. So if you
are using AMD’s SDK, the AMD OpenCL compiler that is part of their OpenCL SDK will be used. Likewise for Nvidia or Intel.

Its important to check the OpenCL status code for ALL OpenCL function calls.
This is mandatory for clCreateProgramWithSource() and clBuildProrgam() to get
any compiler errors or messages. There is a whole other bit code to write
to get the size of the messages and then retrieve the messages themselves.