I have the following code in my server program:

void sendAccounts(const Database& data, int socket, int32_t user)
{
   std::vector<int32_t> accounts = data.getUsersAccounts(user);
   uint16_t number = accounts.size();
   number = htons(number);
   send(socket, reinterpret_cast<char*>(&number), sizeof(number), 0);
   for (size_t i = 0; i < accounts.size();   i)
   {    
        std::cout << accounts[i] << std::endl;
        int32_t account = htonl(accounts[i]);
        send(socket, reinterpret_cast<char*>(&account), sizeof(account), 0);
   }
}

And the following code in my client program:

std::vector<int32_t> getAccounts(int socket)
{
    uint16_t n_accounts;
    std::vector<int32_t> accounts;
    recv(socket, reinterpret_cast<char*>(&n_accounts), sizeof(n_accounts), 0);
    n_accounts = ntohs(n_accounts);
    for (uint16_t i = 0; i < n_accounts;   i)
    {
        int32_t account = 0;
        recv(socket, reinterpret_cast<char*>(account), sizeof(account), 0);
        account = ntohl(account);
        accounts.push_back(account);
    }
    return accounts;
}

For some reason the client correctly receives the number of accounts but unable to receive account numbers, each recv returns -1, when I check errno it is equal to 0. What can be wrong?

CodePudding user response：

In the recv() loop, you are casting the value of account, which is always 0, thus producing a null pointer. This is the main reason why recv() is failing.

You need to instead cast the address of account (just as you did with n_accounts above the loop). So, change this:

reinterpret_cast<char*>(account)

To this:

reinterpret_cast<char*>(&account)

That being said, on most platforms, send() and recv() take void* pointers, so you don't actually need to use reinterpret_cast at all on those platforms.

Since you mention errno, I assume you are not running this code on Windows. If you were, then send()/recv() do take char* pointers and thus would need the casts (and you should be using WSAGetLastError() instead of errno).