Tutorial "Hello World": includes unclean code/commands, gives error

Discussion created by fabtagon on Apr 5, 2010
Latest reply on Apr 8, 2010 by fabtagon
two unclean issues in the tutorial, additionally I get an error with or without them

I started with the tutorial "Hello World" from http://developer.amd.com/GPU/ATISTREAMSDK/pages/TutorialOpenCL.aspx .


First, there are two unclean issues in the tutorial:

i) using gcc for C++

Eventhough we are about to compile C++ code the tutorial tells us to compile using

gcc –o hello_world –Ipath-OpenCL-include –Lpath-OpenCL-libdir lesson1.cpp –lOpenCL

gcc compiles only C code. g++ is responsible for C++. (gcc sometimes works with C++ code under weird circumstances, but generally will result in weird errors)


ii) type missmatch in parameter of getInfo()

(At least in the current version) cl::Platform::getInfo expects its' second argument to be of type cl::string. In the tutorial it is std::string (resulting in compile error).


iii) no compute devices found

While these are just not very suitable for a tutorial intented for beginner, the next one looks like a real problem:

When running I get

ERROR: cl::Platform::get (-1)

This means the very first OpenCL call in the code cl::Platform::get() fails to find any suitable compute device.

Does anybody have an idea what could cause the problem or how to further investigate it?



  • Ubuntu 9.10 AMD64
  • ATI Catalyst 10.2 (glx and compiz enabled and working)
  • ATI Stream SDK 2.01-lnx64
  • AMD Phenom II 905e
  • ATI Radeon HD 4350

edits: markup fixes


#include <utility> #define __NO_STD_VECTOR // Use cl::vector and cl::string and #define __NO_STD_STRING // not STL versions, more on this later #include <CL/cl.hpp> #include <cstdio> #include <cstdlib> #include <fstream> #include <iostream> #include <string> #include <iterator> const std::string hw("Hello World\n"); inline void checkErr(cl_int err, const char * name) { if (err != CL_SUCCESS) { std::cerr << "ERROR: " << name << " (" << err << ")" << std::endl; exit(EXIT_FAILURE); } } int main(void) { cl_int err; cl::vector< cl::Platform > platformList; cl::Platform::get(&platformList); checkErr(platformList.size()!=0 ? CL_SUCCESS : -1, "cl::Platform::get"); std::cerr << "Platform number is: " << platformList.size() << std::endl; //std::string platformVendor; cl::string platformVendor; platformList[0].getInfo(CL_PLATFORM_VENDOR, &platformVendor); std::cerr << "Platform is by: " << platformVendor.c_str() << "\n"; cl_context_properties cprops[3] = {CL_CONTEXT_PLATFORM, (cl_context_properties)(platformList[0])(), 0}; cl::Context context( CL_DEVICE_TYPE_CPU, cprops, NULL, NULL, &err); checkErr(err, "Context::Context()"); char * outH = new char[hw.length()+1]; cl::Buffer outCL( context, CL_MEM_WRITE_ONLY | CL_MEM_USE_HOST_PTR, hw.length()+1, outH, &err); checkErr(err, "Buffer::Buffer()"); cl::vector<cl::Device> devices; devices = context.getInfo<CL_CONTEXT_DEVICES>(); checkErr( devices.size() > 0 ? CL_SUCCESS : -1, "devices.size() > 0"); std::ifstream file("lesson1_kernels.cl"); checkErr(file.is_open() ? CL_SUCCESS:-1, "lesson1_kernel.cl"); 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); err = program.build(devices,""); checkErr(file.is_open() ? CL_SUCCESS : -1, "Program::build()"); cl::Kernel kernel(program, "hello", &err); checkErr(err, "Kernel::Kernel()"); err = kernel.setArg(0, outCL); checkErr(err, "Kernel::setArg()"); cl::CommandQueue queue(context, devices[0], 0, &err); checkErr(err, "CommandQueue::CommandQueue()"); cl::Event event; err = queue.enqueueNDRangeKernel( kernel, cl::NullRange, cl::NDRange(hw.length()+1), cl::NDRange(1, 1), NULL, &event); checkErr(err, "ComamndQueue::enqueueNDRangeKernel()"); event.wait(); err = queue.enqueueReadBuffer( outCL, CL_TRUE, 0, hw.length()+1, outH); checkErr(err, "ComamndQueue::enqueueReadBuffer()"); std::cout << outH; return EXIT_SUCCESS; } #pragma OPENCL EXTENSION cl_khr_byte_addressable_store : enable __constant char hw[] = "Hello World\n"; __kernel void hello(__global char * out) { size_t tid = get_global_id(0); out[tid] = hw[tid]; }