OpenCL char limit

both of the implementations of printsomestuff will only write up to res[7] (i.e.: WORLD!\0 or !ELLOWO\0)

main.cpp:

...
char A[16] = "HELLO ";
        cl::Buffer aBuf(context, CL_MEM_READ_WRITE, sizeof(A));

        char B[16] = "WORLD!";
        cl::Buffer bBuf(context, CL_MEM_READ_WRITE, sizeof(B));

        queue.enqueueWriteBuffer(aBuf, CL_TRUE, 0, sizeof(A) * sizeof(char), A);
        queue.enqueueWriteBuffer(bBuf, CL_TRUE, 0, sizeof(B) * sizeof(char), B);

        char res[16];
        cl::Buffer resBuf(context, CL_MEM_READ_WRITE, sizeof(res) * sizeof(char));

        cl::Kernel kernel(program, "printsomestuff");
        kernel.setArg(0, aBuf);
        kernel.setArg(1, bBuf);
        kernel.setArg(2, resBuf);

        queue.enqueueTask(kernel);
        //queue.enqueueNDRangeKernel(kernel, cl::NullRange, cl::NDRange(32), cl::NullRange);

        queue.enqueueReadBuffer(resBuf, CL_TRUE, 0, sizeof(resBuf), res);

        std::cout << res;
...

my_kernels.cl

kernel void printsomestuff(__global char *A, __global char *B,
                           __global char *res) {

  /*  for (int i = 0; i < 8; i++) {
      res[i] = B[i];
      res[i + 8] = A[i];
    }*/

  res[0] = '!';
  res[1] = 'E';
  res[2] = 'L';
  res[3] = 'L';
  res[4] = 'O';
  res[5] = ' ';
  res[6] = 'W';
  res[7] = 'O';
  res[8] = 'R';
  res[9] = 'L';
  res[10] = 'D';
  res[11] = '!';
  res[12] = '\n';
}

Solution

sizeof(A) when A is a char* is the size of the pointer, not the length of the array. So, if you pass your char A[16] to this function:

kernel void printsomestuff(__global char *A, __global char *B,
                           __global char *res) {

sizeof(A) will be the size of a pointer which is usually 4 or 8 chars. It has no knowledge of the length.

Demo 1

You need to provide the size as a separate parameter or use a type created for carrying data of this type, like a std::string.

If you only have fixed sized char arrays, you could make some adjustment to your functions to make them preserve the array extent, like this:

template<std::size_t Asize, std::size_t Bsize, std::size_t Ressize>
kernel void printsomestuff(__global char (&A)[Asize], __global char (&B)[Bsize],
                           __global char (&res)[Ressize]) {

^{(I don't really know what __global does but I'll leave it in)}

You now have all sizes you need to use in the function.
Demo 2