Download file from SFTP server with libssh and write it to ofstream by using C++?

I wrote the following code from this.

#define MAX_XFER_BUF_SIZE 16384
int main()
{
    char buffer[MAX_XFER_BUF_SIZE];

      //..some content
     access_type = O_RDONLY;
     sftp_file file = sftp_open(sftp, "/home/ra/Desktop/sami/s.txt", access_type, 0);
     ofstream fin("C:/Users/s.txt", ios::binary | ios::in | std::ofstream::out | std::ofstream::app);

     nbytes = sftp_read(file, buffer, sizeof(buffer));
     fin.write(buffer, sizeof(buffer));

But the buffer maximum size is predefined. So it only works for small files. I want to get the SFTP file size which size is much bigger. For that I need to send the data as chunks by append mode.

for (int i=0;i<sizeof(buffer);i++)
{
    fin.write(buffer, buffer[i]);
}

I went through this answer, but i'm stuck in this > How can i solve this issue.

You have removed the loop that is in the Reading a file from the remote computer example.

Return it back. The important part of the example modified to use ofstream is like:

char buffer[MAX_XFER_BUF_SIZE];

// ...

for (;;)
{
    nbytes = sftp_read(file, buffer, sizeof(buffer));
    if (nbytes == 0)
    {
        break; // EOF
    }
    else if (nbytes < 0)
    {
        fprintf(stderr, "Error while reading file: %s\n", ssh_get_error(session));
        sftp_close(file);
        return SSH_ERROR;
    }

    fin.write(buffer, nbytes);
    if (!fin)
    {
        fprintf(stderr, "Error writing");
        sftp_close(file);
        return SSH_ERROR;
    }
}

fin.close();
if (!fin)
{
    fprintf(stderr, "Error writing");
    sftp_close(file);
    return SSH_ERROR;
}

Imo, fin seems like a bad name to me. Shouldn't it be fout ("file output")?