The task sounds simple: “In each process (except 0) you have a set of 1 to 5 numbers. Send each set to main processor with MPI_Bsend, and print those sets in main process in ascending order of the ranks of the sending processes. To get the size of sent sets use MPI_Get_count”.
However, I’m doing something wrong. The program shows an error like this for each process from 1 to 7:

[1] fatal error
Fatal error in MPI_Bsend: Invalid buffer pointer, error stack:
MPI_Bsend(buf=0x000002AE44C39290, count=2, MPI_INT, dest=0, tag=0, MPI_COMM_WORLD) failed
Insufficient space in Bsend buffer; requested 8; total buffer size is 0

Program code is right here:

#include <mpi.h>
#include <iostream>
#include <vector>

using namespace std;

int main(int argc, char** argv) 
{
    int rank, size;
    const int TAG = 0;

    MPI_Init(&argc, &argv);
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
    MPI_Comm_size(MPI_COMM_WORLD, &size);

    srand(time(0) + rank);

    if (rank == 0) 
    {
        vector<vector<int>> data(size - 1);

        for (int i = 1; i < size; i++) 
        {
            MPI_Status status;
            int count = 0;

            MPI_Probe(i, TAG, MPI_COMM_WORLD, &status);
            MPI_Get_count(&status, MPI_INT, &count);
            data[i - 1].resize(count);

            MPI_Recv(data[i - 1].data(), count, MPI_INT, i, TAG, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
        }

        for (int i = 0; i < data.size(); i++) 
        {
            cout << "Process " << i + 1 << " sent: ";
            for (int num : data[i])
                cout << num << " ";
            cout << endl;
        }
    }
    else 
    {
        int N;
        vector<int> numbers;

        N = rand() % 5 + 1;
        numbers.resize(N);
        for (int i = 0; i < N; i++)
            numbers.push_back(rand() % 100);

        cout << "Process " << rank << " initialized with values: ";
        for (int i = 0; i < N; i++)
            cout << numbers[i] << " ";
        cout << endl;

        MPI_Bsend(numbers.data(), N, MPI_INT, 0, TAG, MPI_COMM_WORLD);
    }

    MPI_Finalize();

    return 0;
}

I guess the main problem lies in the moment when I try to recv vectors with sizes of the messages that I got from the processes that do the Bsend, but have no actual clue how to fix this. Any ideas?