thrust::for_each_n

Defined in thrust/for_each.h

template<typename DerivedPolicy, typename InputIterator, typename Size, typename UnaryFunction> InputIterator thrust::for_each_n(const thrust::detail::execution_policy_base<DerivedPolicy> &exec, InputIterator first, Size n, UnaryFunction f)

for_each_n applies the function object f to each element in the range [first, first + n); f's return value, if any, is ignored. Unlike the C++ Standard Template Library function std::for_each, this version offers no guarantee on order of execution.

The algorithm’s execution is parallelized as determined by exec.

The following code snippet demonstrates how to use for_each_n to print the elements of a device_vector using the thrust::device parallelization policy.

#include <thrust/for_each.h>
#include <thrust/device_vector.h>
#include <thrust/execution_policy.h>
#include <cstdio>

struct printf_functor
{
  __host__ __device__
  void operator()(int x)
  {
    // note that using printf in a __device__ function requires
    // code compiled for a GPU with compute capability 2.0 or
    // higher (nvcc --arch=sm_20)
    printf("%d\n", x);
  }
};
...
thrust::device_vector<int> d_vec(3);
d_vec[0] = 0; d_vec[1] = 1; d_vec[2] = 2;

thrust::for_each_n(thrust::device, d_vec.begin(), d_vec.size(), printf_functor());

// 0 1 2 is printed to standard output in some unspecified order