网络编程学习笔记(getsockopt和setsockopt函数)

其原型为：

#include <sys/socket.h>
int getsockopt(int sockfd, int level, int optname, void *optval, socklen_t *optlen);
int setsockopt(int sockfd, int level, int optname, const void *optval, socklen_t optlen);

成功返回0, 失败返回-1

其代码如下：

#include <sys/socket.h>
#include <unistd.h>
#include <stdio.h>
#include <netinet/tcp.h>
#include <sys/time.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <netinet/in.h>union val
{int i_val;long l_val;char c_val[10];struct linger linger_val;struct timeval timeval_val;
}val;static char *sock_str_flag(union val*, int);
static char *sock_str_int(union val*, int);
static char *sock_str_linger(union val*, int);
static char *sock_str_timeval(union val*, int);struct sock_opts
{char *opt_str;int opt_level;int opt_name;char *(*opt_val_str)(union val*, int);
}sock_opts[] = {"SO_BROADCAST", SOL_SOCKET, SO_BROADCAST, sock_str_flag,"SO_DEBUG", SOL_SOCKET, SO_DEBUG, sock_str_flag,"SO_DONTROUTE", SOL_SOCKET, SO_DONTROUTE, sock_str_flag,"SO_ERROR", SOL_SOCKET, SO_ERROR, sock_str_int,"SO_KEEPALIVE", SOL_SOCKET, SO_KEEPALIVE, sock_str_flag,"SO_LINGER", SOL_SOCKET, SO_LINGER, sock_str_linger,"SO_OOBINLINE", SOL_SOCKET, SO_OOBINLINE, sock_str_flag,"SO_RCVBUF", SOL_SOCKET, SO_RCVBUF, sock_str_int,"SO_SNDBUF", SOL_SOCKET, SO_SNDBUF, sock_str_int,"SO_RCVLOWAT", SOL_SOCKET, SO_RCVLOWAT, sock_str_int, "SO_SNDLOWAT", SOL_SOCKET, SO_SNDLOWAT, sock_str_int,"SO_RCVTIMEO", SOL_SOCKET, SO_RCVTIMEO, sock_str_timeval,"SO_SNDTIMEO", SOL_SOCKET, SO_SNDTIMEO, sock_str_timeval,"SO_REUSEADDR", SOL_SOCKET, SO_REUSEADDR, sock_str_flag,#ifdef SO_REUSEPORT"SO_REUSEPORT", SOL_SOCKET, SO_REUSEPORT, sock_str_flag,#else"SO_REUSEPROT", 0, 0, NULL,#endif"SO_TYPE", SOL_SOCKET, SO_TYPE, sock_str_int,//"SO_USELOOPBACK", SOL_SOCKET, SO_USELOOPBACK, sock_str_flag,"IP_TOS", IPPROTO_IP, IP_TOS, sock_str_int,"IP_TTL", IPPROTO_IP, IP_TTL, sock_str_int,"TCP_MAXSEG", IPPROTO_TCP, TCP_MAXSEG, sock_str_int,"TCP_NODELAY", IPPROTO_TCP, TCP_NODELAY, sock_str_flag,NULL, 0, 0, NULL};static char strres[128];
static char *sock_str_flag(union val* ptr, int len)
{if (len != sizeof(int)) {snprintf(strres, sizeof(strres), "size (%d) not sizeof(int)", len);} else {snprintf(strres, sizeof(strres), "%s", (ptr->i_val == 0) ?"off": "on");}return strres;
}static char *sock_str_int(union val* ptr, int len)
{if (len != sizeof(int)) {snprintf(strres, sizeof(strres), "size (%d) not sizeof(int)", len);} else {snprintf(strres, sizeof(strres), "%d", ptr->i_val);}   return strres;
}static char *sock_str_linger(union val* ptr, int len)
{if (len != sizeof(struct linger)) {snprintf(strres, sizeof(strres), "size (%d) not sizeof(struct linger)", len);} else {snprintf(strres, sizeof(strres), "l_onoff=%d, l_linger=%d", ptr->linger_val.l_onoff, ptr->linger_val.l_linger);}return strres;
}static char *sock_str_timeval(union val* ptr, int len)
{if (len != sizeof(struct timeval)) {snprintf(strres, sizeof(strres), "size (%d) not sizeof(struct timeval)", len);} else {snprintf(strres, sizeof(strres), "tv_sec=%d, tv_usec=%d", ptr->timeval_val.tv_sec, ptr->timeval_val.tv_usec);}return strres;
}int main(int argc, char **argv)
{int fd, len;struct sock_opts *ptr;fd = socket(AF_INET, SOCK_STREAM, 0);   for (ptr = sock_opts; ptr->opt_str != NULL; ptr++) {printf("%s:", ptr->opt_str);if (ptr->opt_val_str == NULL) {printf("undefined\n");} else {len = sizeof(val);if (getsockopt(fd, ptr->opt_level, ptr->opt_name, &val, &len) == -1) {printf("error:%s\n", strerror(errno));return -1;} else {printf("default: %s\n", ptr->opt_val_str(&val, len));}}}return 0;
}

SO_USELOOPBACK竟然找不到定义

运行后输出截图如下：

套接口的选项：

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