typedef struct point_struct { int x, y; }point;

int num_item =2;
int blocklengths[2] = {1,1};
MPI_Datatype types[2] = {MPI_INT, MPI_INT};
MPI_Datatype mpi_point_type;
MPI_Aint offsets[2];
offsets[0] = offsetof(point, x);
offsets[1] = offsetof(point, y);
MPI_Type_create_struct(num_item, blocklengths, offsets, types, &mpi_point_type );
MPI_Type_commit(&mpi_point_type);

point p_x[n];

point *p_x = (struct point_struct*)malloc(n*sizeof(struct point_struct));