linux - Server-client in C: Weird behaviour when sending bytes -

i'm trying write server-client program in c wherein client send bunch of messages in form of 5 bytes: first byte contain command, , next 4 contain key. looks this:

rc = write(sockfd, &op, 1);     if (rc != 1)     {         printf("error! write() failed: %s\n", strerror(errno));         break;     }      uint32_t net_num = htonl(num);     int nsent = 0;     while (nsent < 4)     {         rc = write(sockfd, &net_num + nsent, 4 - nsent);         if (rc <= 0)         {             printf("error! write() failed: %s\n", strerror(errno));             break;         }          nsent += rc;     }      if (rc <= 0)         break; } 

on receiving end, have:

 while((bytes = recv(socket,buffer,5,0)) > 0)     {         //printf("%d\t%d\t%d\t%d\t%d\n",(int)buffer[0],(int)buffer[1],      (int)buffer[2],(int)buffer[3],(int)buffer[4]);         key = ((buffer[4] << 24) | (buffer[3] << 16) | (buffer[2] << 8) | (buffer[1]));          if((int)buffer[0] == 0)         {              command 0, etc... 

the problem i'm having cant key. i've tried switching order of shifts, i'm getting numbers don't match keys client sending. i'm @ loss.

even stranger, if compile server without print under while, seg-faulted. if uncomment printf, works fine. seems super strange.

does know might causing this? in advance.

rc = write(sockfd, &net_num + nsent, 4 - nsent); wrong, &net_num pointer 32 bits object, &net_num+1 point next 32bits object. beyond object. cast char pointer, or copy small char buffer before sending, below:

---

uint32_t net_num = htonl(num); char buff[sizeof net_num]; memcpy (buff, &net_num, sizeof buff);  int nsent; nsent=0; nsent < sizeof buff; nsent += rc;) {     rc = write(sockfd, buff + nsent, 4 - nsent);     if (rc == -1 && errno == eagain) { rc=0; continue; }     if (rc <= 0)     {         printf("error! write() failed: %s\n", strerror(errno));         break;     }   }