c - How to avoid default construction of elements in thrust::device_vector? -

1. it seems when creating new thrust vector all elements 0 default - want confirm case.

2. if so, there way bypass constructor responsible behavior additional speed (since vectors don't need them have initial value, e.g. if raw pointers being passed cublas output)?

thrust::device_vector constructs elements contains using supplied allocator, std::vector. it's possible control allocator when vector asks construct element.

use custom allocator avoid default-initialization of vector elements:

// uninitialized_allocator allocator // derives device_allocator , has // no-op construct member function template<typename t>   struct uninitialized_allocator     : thrust::device_malloc_allocator<t> {   // note construct annotated   // __host__ __device__ function   __host__ __device__   void construct(t *p)   {     // no-op   } };  // make device_vector not initialize elements, // use uninitialized_allocator 2nd template parameter typedef thrust::device_vector<float, uninitialized_allocator<float> > uninitialized_vector; 

you still incur cost of kernel launch invoke uninitialized_allocator::construct, kernel no-op retire quickly. you're interested in avoiding memory bandwidth required fill array, solution does.

there's complete example code here.

note technique requires thrust 1.7 or better.