How to send(MPI_Send) nested structure having pointer fields in MPI using C

Question

I have a structure :

    struct vertex 
    {  
     double a; double b;
    }      

    struct polygon
    {
     int numofVertex;
     vertex *v;
    }


        

Answer 1

You'll have to send it in two messages:

// 'p' is a pointer to your polygon
vertex *tmp = p->v;
p->v = NULL;
MPI_Send(p, sizeof(struct polygon), MPI_BYTES, dest, 1, ...);
MPI_Send(tmp, sizeof(struct vertex), MPI_BYTES, dest, 2, ...);
p->v = tmp;

On the receiving end, you simply receive the struct in two steps:

polygon p;
MPI_Recv(&p, sizeof(struct polygon), MPI_BYTES, src, 1, ...);
p.vertex = malloc(sizeof(struct vertex));
MPI_Recv(p.vertex, sizeof(struct vertex), MPI_BYTES, src, 2, ...);

Obviously this is not very nice, so it'll be easier if you keep your struct pointer-less so you can send it at once.