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16.6. Socket Options[View full width]#include <sys/socket.h> int setsockopt(int sockfd , int level , int option ,  const void *val ,socklen_t len ); |
| Returns: 0 if OK, 1 on error |
int getsockopt(int sockfd , int level , int option ,
void *restrict val ,socklen_t *restrict lenp );
Example
The function in Figure 16.10 fails to operate properly when the server terminates and we try to restart it immediately. Normally, the implementation of TCP will prevent us from binding the same address until a timeout expires, which is usually on the order of several minutes. Luckily, the SO_REUSEADDR socket option allows us to bypass this restriction, as illustrated in Figure 16.20.To enable the SO_REUSEADDR option, we set an integer to a nonzero value and pass the address of the integer as the val argument to setsockopt. We set the len argument to the size of an integer to indicate the size of the object to which val points.
Figure 16.20. Initialize a socket endpoint for use by a server with address reuse
#include "apue.h"
#include <errno.h>
#include <sys/socket.h>
int
initserver(int type, const struct sockaddr *addr, socklen_t alen,
int qlen)
{
int fd, err;
int reuse = 1;
if ((fd = socket(addr->sa_family, type, 0)) < 0)
return(-1);
if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &reuse,
sizeof(int)) < 0) {
err = errno;
goto errout;
}
if (bind(fd, addr, alen) < 0) {
err = errno;
goto errout;
}
if (type == SOCK_STREAM || type == SOCK_SEQPACKET) {
if (listen(fd, qlen) < 0) {
err = errno;
goto errout;
}
}
return(fd);
errout:
close(fd);
errno = err;
return(-1);
}
