library is linked but reference is undefined

Question

I\'m trying to compile an openCL program on Ubuntu with an NVIDIA card that worked once before,

#include 
#include 
#include &         


        

Answer 1

Alternatively you can add the header and library path to your global variables.

export CPLUS_INCLUDE_PATH=$CPLUS_INCLUDE_PATH:/usr/local/cuda/include
export LIBRARY_PATH=$LIBRARY_PATH:/usr/lib/nvidia-current

You can also try to set

export PATH=$PATH:/usr/local/cuda/bin

It should be possible to run now

g++ opencl.cpp

Answer 2

From the gcc man page:

   -llibrary
   -l library
       Search the library named library when linking.  (The second alternative with the library as a separate argument is only for POSIX compliance and is not recommended.)

       It makes a difference where in the command you write this option; the linker searches and processes libraries and object files in the order they are specified.  Thus, foo.o
       -lz bar.o searches library z after file foo.o but before bar.o.  If bar.o refers to functions in z, those functions may not be loaded.

       The linker searches a standard list of directories for the library, which is actually a file named liblibrary.a.  The linker then uses this file as if it had been specified
       precisely by name.

So try to specify the -lOpenCL after the file argument in your compile command.

You also search for symbols in libOpenCL.so, which is a shared library file. With your command you link your program agains a static library, in the format libOpenCL.a.

Answer 3

when you are linking, the order of your libraries and source files makes a difference. for example for your case,

g++ -I/usr/local/cuda/include -L/usr/lib/nvidia-current -lOpenCL opencl.cpp

functions defined in the OpenCL library might not be loaded, since there nothing before them asking for a look-up. however if you use,

g++ opencl.cpp -I/usr/local/cuda/include -L/usr/lib/nvidia-current -lOpenCL  

then any requests for functions will be found in the OpenCL library and they will be loaded.