Question

Rookie question FYI.

Whenever I compile/run the code, extern tolayer2(rtpktTo1); I receive a warning.
The warning reads, as in the title, Warning: parameter names (without types) in function declaration

Any help appreciated.

node0.c

extern struct rtpkt {
  int sourceid;       /* id of sending router sending this pkt */
  int destid;         /* id of router to which pkt being sent 
                         (must be an immediate neighbor) */
  int mincost[4];    /* current understanding of min cost to node 0 ... 3 */
  };

/* Create routing packets (rtpkt) and send to neighbors via tolayer2(). */
    struct rtpkt rtpktTo1;
        rtpktTo1.sourceid = 0;
        rtpktTo1.destid = 1;
        rtpktTo1.mincost[0] = minCost[0];
        rtpktTo1.mincost[1] = minCost[1];
        rtpktTo1.mincost[2] = minCost[2];
        rtpktTo1.mincost[3] = minCost[3];

extern tolayer2(rtpktTo1);

prog3.c

tolayer2(packet)
  struct rtpkt packet;
{
  /* This has a lot of code in it */ 
}

Answer 1

The assignments to rkpktTo1.* are not apparently in a function or declaration, unless this is a code fragment. Wrap them in a function. The warning is a bit misleading.

The declaration of tolayer2() should have a return type as well as a parameter type. Since there isn’t one, int is assumed. This may not be what is intended, but it should compile without warnings and errors:

node0.c

struct rtpkt {
  int sourceid;       /* id of sending router sending this pkt */
  int destid;         /* id of router to which pkt being sent 
                         (must be an immediate neighbor) */
  int mincost[4];    /* current understanding of min cost to node 0 ... 3 */
  };

/* Create routing packets (rtpkt) and send to neighbors via tolayer2(). */
void function () {
    struct rtpkt rtpktTo1;
        rtpktTo1.sourceid = 0;
        rtpktTo1.destid = 1;
        rtpktTo1.mincost[0] = minCost[0];
        rtpktTo1.mincost[1] = minCost[1];
        rtpktTo1.mincost[2] = minCost[2];
        rtpktTo1.mincost[3] = minCost[3];
}
extern void tolayer2(struct rtpkt *rtpktTo1);

prog3.c

void
tolayer2(struct rtpkt *packet)
{
  /* This has a lot of code in it */ 
}

Passing a structure by value is often not appropriate, so I have changed it to pass by reference.