title: preferred vector width in opencl device
body: <p>I'm a beginner in OpenCL and am trying to run the sample codes of the "OpenLC in Action" book. I have the following code to get the preferred vector width of my device. The platforms detected on my computer are from Intel Core i7 and HD graphics and another one from NVIDIA GeForce 940M. Whenever I run the code, it gives "1" for vector width of every type unless type double which is zero because it is not supported. Even when I change the platform in my computer to check its devices, results are the same. I ran the code on an AMD computer and it seemed to work properly because it gave me different numbers for different types. But, I am not sure why this code keeps giving me "1" for every type on different platforms of my computer. Any ideas?
  Here is the output:
  <a href="https://i.stack.imgur.com/363Zz.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/363Zz.png" alt="enter image description here"></a></p>
  
  <p>Here is the code:</p>
  
  <pre><code>#include &lt;stdio.h&gt;
  #include &lt;stdlib.h&gt;
  #include &lt;string.h&gt;
  #include &lt;CL/cl.h&gt;
  
  int main(){
  
      cl_int err, i, j;
      cl_platform_id *platforms;
      cl_device_id *devices;
      cl_uint num_platforms, num_devices, vector_width;
      size_t plat_name_size, devi_name_size;
      char *plat_name_data, *devi_name_data;
  
  
      err = clGetPlatformIDs(1, NULL, &amp;num_platforms);
      if (err &lt; 0){
          perror("No platform is found");
          exit(1);
      }
      platforms = (cl_platform_id*)malloc(sizeof(cl_platform_id)*num_platforms);
      clGetPlatformIDs(num_platforms, platforms, NULL);
  
      printf("Number of found platforms is %d\n ", num_platforms);
  
      for (i = 0; i &lt; num_platforms; i++){
  
          err = clGetPlatformInfo(platforms[i], CL_PLATFORM_NAME, 0, NULL, &amp;plat_name_size);
          if (err &lt; 0){
              perror("Couldn't read platform name.");
              exit(1);
          }
          plat_name_data = (char*)malloc(plat_name_size);
          clGetPlatformInfo(platforms[i], CL_PLATFORM_NAME, plat_name_size, plat_name_data, NULL);
          printf("Platform No.%d is: %s\n", i, plat_name_data);
  
          err = clGetDeviceIDs(platforms[i], CL_DEVICE_TYPE_ALL, 1, NULL, &amp;num_devices);
          if (err &lt; 0){
              perror("No device is found in this platform");
              exit(1);
          }
          devices = (cl_device_id*)malloc(sizeof(cl_device_id)*(num_devices));
          clGetDeviceIDs(platforms[i], CL_DEVICE_TYPE_ALL, num_devices, devices, NULL);
          printf("Number of devices found in this platform is: %d\n", num_devices);
          for (j = 0; j &lt; num_devices; j++){
              err = clGetDeviceInfo(devices[j], CL_DEVICE_NAME, 0, NULL, &amp;devi_name_size);
              if (err &lt; 0){
                  perror("Couldn't read the device name.");
                  exit(1);
              }
              devi_name_data = (char*)malloc(devi_name_size);
              clGetDeviceInfo(devices[j], CL_DEVICE_NAME, devi_name_size, devi_name_data, NULL);
              printf("Device No.%d name is: %s\n", j + 1, devi_name_data);
              if (strstr(devi_name_data, "GeForce 940M")){
                  clGetDeviceInfo(devices[j], CL_DEVICE_PREFERRED_VECTOR_WIDTH_CHAR, 
                      sizeof(cl_uint), &amp;vector_width, NULL);
                  printf("Preferred vector width in chars: %u\n", vector_width);
                  clGetDeviceInfo(devices[j], CL_DEVICE_PREFERRED_VECTOR_WIDTH_SHORT,
                      sizeof(cl_uint), &amp;vector_width, NULL);
                  printf("Preferred vector width in shorts: %u\n", vector_width);
                  clGetDeviceInfo(devices[j], CL_DEVICE_PREFERRED_VECTOR_WIDTH_INT,
                      sizeof(cl_uint), &amp;vector_width, NULL);
                  printf("Preferred vector width in ints: %u\n", vector_width);
                  clGetDeviceInfo(devices[j], CL_DEVICE_PREFERRED_VECTOR_WIDTH_LONG,
                      sizeof(cl_uint), &amp;vector_width, NULL);
                  printf("Preferred vector width in longs: %u\n", vector_width);
                  clGetDeviceInfo(devices[j], CL_DEVICE_PREFERRED_VECTOR_WIDTH_FLOAT,
                      sizeof(cl_uint), &amp;vector_width, NULL);
                  printf("Preferred vector width in floats: %u\n", vector_width);
                  clGetDeviceInfo(devices[j], CL_DEVICE_PREFERRED_VECTOR_WIDTH_DOUBLE,
                      sizeof(cl_uint), &amp;vector_width, NULL);
                  printf("Preferred vector width in doubles: %u\n", vector_width);
              }
          }
  
      }
      return 0;
  }
  </code></pre>