socketC.c

/* basic socket operations, UNIX-native */

 /* pointer arithmetics:
  *
  * push(pointer, v) INDICATES *(pointer++) = v
  * pop(pointer) INDICATES *(--pointer)
  * (*++v)[0] INDICATES (**++v)
  *           INDICATES first char in v
  *           INDICATES name of string/vector v
  * likewise, *v[0] INDICATES **v
  *       and *v[n] INDICATES **(v + n)
  * returntype (*funct)(args) INDICATES a function funct with arguments args which returns...
  * char **argv INDICATES pointer to char pointer
  * int(*v)[len] INDICATES pointer "v" to a vector of "len" int elements
  * int *v[len] INDICATES vector "v" of "len" pointers to int elements
  * void *funct() INDICATES function "funct" that returns a pointer-to-void
  * void (*funct)() INDICATES pointer to a function "funct" that returns void
  *
  */

 /* useful characters: [] # */

 # include <stdio.h>
 # include <stdlib.h> // for exit
 # include <sys/types.h>
 # include <sys/socket.h>
 # include <netinet/in.h>
 # include <netdb.h>

 # define SIZE 1024
 # define exception(x) { puts(x); exit(1); }

 int main(int argc, char * argv[])
    {
     /* recvfrom */
     int sock;
     struct sockaddr_in mysock;
     struct sockaddr addr;
     int addrlen;
     char buffer[SIZE]; // stores data
     sock = socket(AF_INET, SOCK_DGRAM, 0); // UDP socket
     mysock.sin_family = AF_INET;
     mysock.sin_port = 1999;
     mysock.sin_addr.s_addr = INADDR_ANY;
     bind(sock, &mysock, sizeof(mysock)); // binding sock and mysock
     // COMMENTED LINE BELOW causes infinite loop, why?
     //if(recvfrom(sock, buffer, SIZE, 0, &addr, &addrlen) == -1) // done receiving condition
    exception("Call error in recvfrom(...)\n");


     /* sendto */
     /* SOCK, MYSOCK and BUFFER will be used without being reinstanced */
     int success;
     struct hostent * hp;
     hp = gethostbyname("dis.uniroma1.it");
     memcpy(&mysock.sin_addr, hp->h_addr, 4);
     success = sendto(sock, buffer, SIZE, 0, &mysock, sizeof(mysock));
     if(success == -1) exception("Call error in sendto(...)\n");

     return 0;
    }