Can't assign char numeric value in kernel

I am having a silly problem I just can’t figure out. In my kernel I want to use a char array to hold values in the range 0-255 but am unable to do so, when I read back the char array on the host side it has no values in it. I have a simple test kernel that tries to fill the output array with the char values 1 through 10 as an example of my problem and have tested it on Apples OpenCL implementation as well as NVIDIA’s so I assume i’m doing something wrong. If I make the output array of type int it works correctly. Thanks in advance

I use the khronos provided C++ bindings:


#include <iostream>
#include <fstream>
#include "cl.hpp"

int main(void)
	cl_int err = CL_SUCCESS;
	cl::Context context(CL_DEVICE_TYPE_GPU, 0, NULL, NULL, &err); 
	std::vector<cl::Device> devices = context.getInfo<CL_CONTEXT_DEVICES>();
	char * outH = new char[10];
	cl::Buffer outCL(context,CL_MEM_WRITE_ONLY| CL_MEM_USE_HOST_PTR,sizeof(cl_char)*10,outH,
	std::ifstream file("");
	std::string prog(std::istreambuf_iterator<char>(file),(std::istreambuf_iterator<char>()));
	cl::Program::Sources source(1,std::make_pair(prog.c_str(), prog.length()+1));
	cl::Program program(context, source);,"");
	cl::Kernel kernel(program, "testKernel", &err);
	kernel.setArg(0, outCL);
	cl::CommandQueue queue(context, devices[0], 0, &err);
	cl::Event event;
									cl::NDRange(1, 1), 
	for (int i=0; i<10; i++) {
    return 0;


#pragma OPENCL EXTENSION cl_khr_byte_addressable_store : enable

__constant char charArray[] = {1,2,3,4,5,6,7,8,9,10};

__kernel void testKernel(__global int * out)
	size_t tid = get_global_id(0);
	out[tid] = charArray[tid];

Sorry, I had a typo in the posted kernel, the global array on the device should be type char, not type int to duplicate the problem:

__kernel void testKernel(__global char * out)

Do you get any errors? I don’t see any error checking code, but perhaps the C++ framework translates them all into exceptions. If you’re on MacOS X you can just set CL_LOG_ERRORS=stdout.

Yes, I removed the try/catch statement to make the code a little shorter and just tried CL_LOG_ERRORS=stdout and neither of them shows an error.