recv return after 0x0000 byte found

Question

Here is my code:

• Client

  Position pos(1.0,2.0,0.45);
  feedback feed(12, pos, 100);
  msgpack::sbuffer sbuf;
  msgpack::pack(sbuf, feed);          
  int test = write(tcp_client.sockfd, sbuf.data(),sizeof(sbuf));
  

• Server :

  char* buffer = new char[41];
  int test = recv(TCP_server.newsockfd, buffer, 40, MSG_WAITALL );
  
  for (int i=0; i< sizeof(buffer); i++)
  std::cout << std::hex << (int)buffer[i] << " ";
  std::cout << std::endl;
  

For the other parts of the codes, connection is established and data has been transmitted successfully.

The problem now is that I got the following output :

• Client :

  ffffff94 b c ffffff93 ffffffca 3f ffffff80 0 0 ffffffca 40 0 0 0 ffffffca 3e ffffffe6 66 66 64
  

• Server :

  ffffff94 b c ffffff93 ffffffca 3f ffffff80 0
  

  Is there any reason why received data stopped after encountering the first 0x0000 char? when I send a string, everything works fine but not in this specific case.

For the records, the recv() doc doesn't help much...

Answer 1

When you call recv, you should use the returned value from that function to determine the number of bytes you should process.

Instead, you used sizeof(buffer) to determine the number of times to loop, which is not correct. The buffer is a char *, and sizeof(char *) will usually be either 4 or 8, depending on 32 / 64 bit.

So this:

for (int i=0; i< sizeof(buffer); i++)

should be:

int test = recv(TCP_server.newsockfd, buffer, 40, MSG_WAITALL );
// assuming that test >= 0
for (int i=0; i < test; i++)