c++ - How to pass additional array to Thrust's min_element predicate -

i'm trying use thrust's min_element reduction find next edge in prim's algorithm. iterate on graph edges. comparison function:

struct compareedge {     __host__ /*__device__*/ bool operator()(edge l, edge r) {         if (visited[l.u] != visited[l.v] && visited[r.u] != visited[r.v]) {             return l.cost < r.cost;         } else if (visited[l.u] != visited[l.v]) {             return true;         } else {             return false;         }     } }; 

unfortunately code cannot run on device, because use visited array, mark visited nodes. how can pass array predicate make usable device-executed code?

there number of ways can handled. present 1 approach. please note question how pass arbitrary data set functor, i'm trying show. i'm not trying address question of whether or not proposed functor useful comparison predicate thrust::min_element (which i'm not sure of).

one approach have statically defined array:

__device__ int d_visited[dsize]; 

then in host code, before using functor, need initialize array:

cudamemcpytosymbol(d_visited, visited, dsize*sizeof(int)); 

your functor code have modified. since may want functor usable either on host or device, need control code based on this:

struct compareedge {     __host__ __device__ bool operator()(edge l, edge r) { #ifdef __cuda_arch__         if (d_visited[l.u] != d_visited[l.v] && d_visited[r.u] != d_visited[r.v]) {             return l.cost < r.cost;         } else if (d_visited[l.u] != d_visited[l.v]) {             return true;         } else {             return false;         } #else         if (visited[l.u] != visited[l.v] && visited[r.u] != visited[r.v]) {             return l.cost < r.cost;         } else if (visited[l.u] != visited[l.v]) {             return true;         } else {             return false;         } #endif     } };