mpi - How do I use MPI_Allgather -

i'm testing out mpi_allgather, , i'm getting strange results... following code gives me output of: "p0 received: 0,42,-1780253336,42,". correct result there 1st one, they're sending ranks. output should be: "0, 1, 2, 3,". i'm @ loss why isn't working expected.

int main(int argc, char* argv[]) {     int rank = 0;     int size = 0;     mpi_init(&argc,&argv);     mpi_comm_rank(mpi_comm_world,&rank);     mpi_comm_size(mpi_comm_world, &size);      int* arr = new int[4];      mpi_allgather(&rank, 1, mpi_int, arr, 4, mpi_int, mpi_comm_world);      if(rank == 0)     {     printf("p0 received: ");     for(int i=0; i< 4; i++)         printf("%i,", arr[i]);     printf("\n");     }     delete arr;     mpi_finalize(); }