title: OPENCV CUDA -- getCudaEnabledDeviceCount return 0
body: <p>I am a fresh to opencv with cuda.
  I use opencv2.4.6 and CUDA4.2.
  I have successfuly compile the opencv with cuda.
  when i use the code:</p>
  
  <pre><code>int cuda_count;
  cudaError_t error = cudaGetDeviceCount( &amp;cuda_count );
  </code></pre>
  
  <p>it returns <code>cudaSuccess</code> and <code>cuda_count=1</code>
  But, when i use the code:</p>
  
  <pre><code>int num_devices = cv::gpu::getCudaEnabledDeviceCount();
  </code></pre>
  
  <p>the <code>num_devices returns 0</code>
  why?</p>
  
  <p>my complete code is:</p>
  
  <pre><code>int main()
  {
  
  int num_devices = cv::gpu::getCudaEnabledDeviceCount();
  
      int cuda_count;
      cudaError_t error = cudaGetDeviceCount( &amp;cuda_count );
  
      if(num_devices &lt;=0 )
      {
          std::cerr &lt;&lt; "no" &lt;&lt; std::endl;
          return -1;
      }
  
      int enable_devivce_id = -1;
  }
  </code></pre>