自从我放入 select 语句后，我的 UDP 服务器在接受任何输入时遇到问题。目的是等待来自 2 个不同套接字（具有不同端口）的数据包。同时我也希望它能够告诉服务器何时想要向同步侦听的端口之一发送某些内容。在下面的代码中，程序运行直到到达
select()writefdsFD_ISSET#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <sys/select.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#define MYPORT "20444" // the port users will be connecting to
#define MAXBUFLEN 1024 //maximum packet length
#define SERVER_R 142.66.140.13 //Server to the "right" of current
#define RTEX_R_PORT "20445" //Port for routing table exchange
typedef enum {false, true} bool;
/*struct to store packet fields into
seq: sequence number;
type: message type; send get ACK
src: client's unique 10 digit number
dst: destination's unique 10 digit number
payload: the message being transferred, if there is any
*/
struct packet
{
char seq[4];
char type[5];
char src[11];
char dst[11];
char payload[MAXBUFLEN];
};
// get sockaddr, IPv4 or IPv6:
void *get_in_addr(struct sockaddr *sa)
{
if (sa->sa_family == AF_INET) {
return &(((struct sockaddr_in*)sa)->sin_addr);
}
return &(((struct sockaddr_in6*)sa)->sin6_addr);
}
int main(void)
{
//rr: reading from server to the "right"
//rw: writing to the server to the "right"
int sockfd, rtex_rr_sockfd, rtex_rw_sockfd, rv, rrr, rrw, numbytes, i, j, first, max_fd;
struct addrinfo hints, *servinfo, *p, *p2, *p3;
struct sockaddr_storage their_addr, right_addr;
fd_set readfds, writefds;
char buf[MAXBUFLEN];
char temp_buf[MAXBUFLEN];
char d_to_s[MAXBUFLEN];
char *field;
socklen_t addr_len;
char s[INET6_ADDRSTRLEN];
FILE *m_storage;
struct packet inet_packet;
static const struct packet EmptyPacket;
static int rt[51][4];
bool re_exists=false;
bool rt_empty=true;
struct timeval tv;
memset(&hints, 0, sizeof hints);//"zero out" the hints struct
hints.ai_family = AF_UNSPEC; // set to AF_INET to force IPv4
hints.ai_socktype = SOCK_DGRAM;
hints.ai_flags = AI_PASSIVE; // use my IP
//prepare socket address structures and store them in servinfo and store in linked list
if ((rv = getaddrinfo(NULL, MYPORT, &hints, &servinfo)) != 0) {
fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
return 1;
}
// loop through all the results and bind to the first we can
for(p = servinfo; p != NULL; p = p->ai_next) {
if ((sockfd = socket(p->ai_family, p->ai_socktype,
p->ai_protocol)) == -1) {
perror("listener: socket");
continue;
}
if (bind(sockfd, p->ai_addr, p->ai_addrlen) == -1) {
close(sockfd);
perror("listener: bind");
continue;
}
break;
}
if (p == NULL) {
fprintf(stderr, "listener: failed to bind socket\n");
return 2;
}
if ((rrr = getaddrinfo(NULL, RTEX_R_PORT, &hints, &servinfo)) != 0) {
fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rrr));
return 1;
}
for(p2 = servinfo; p2 != NULL; p2 = p2->ai_next) {
if ((rtex_rr_sockfd = socket(p2->ai_family, p2->ai_socktype,
p2->ai_protocol)) == -1) {
perror("listener: socket");
continue;
}
if (bind(rtex_rr_sockfd, p2->ai_addr, p2->ai_addrlen) == -1) {
close(rtex_rr_sockfd);
perror("listener: bind");
continue;
}
break;
}
if (p2 == NULL) {
fprintf(stderr, "listener: failed to bind socket\n");
return 2;
}
if((rrw = getaddrinfo(NULL, RTEX_R_PORT, &hints, &servinfo)) != 0) {
fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rrw));
return 1;
}
for(p3 = servinfo; p3 != NULL; p3 = p3->ai_next) {
if((rtex_rw_sockfd = socket(p3->ai_family, p3->ai_socktype,
p3->ai_protocol)) == -1) {
perror("server: socket");
continue;
}
break;
}
if (p3 == NULL) {
fprintf(stderr, "listener: failed to bind socket\n");
return 2;
}
//free up memory no longer needed after binding has completed
freeaddrinfo(servinfo);
FD_ZERO(&readfds);
FD_ZERO(&writefds);
FD_SET(rv, &readfds);
FD_SET(rrr, &readfds);
FD_SET(rrw, &writefds);
printf("Listen Mode\n");
//main while loop, listens for packets.
//Upon receipt of packet, information is stored in a struct for processing.
first=0;
while(1)
{
i=0;
inet_packet = EmptyPacket;
rt_empty=true;
tv.tv_sec = 50;
if(rv > rrr && rv > rrw)
max_fd = (rv + 1);
else if(rrr > rv && rrr > rrw)
max_fd = (rrr + 1);
else if(rrw > rv && rrw > rrr)
max_fd = (rrw + 1);
printf("before select...\n");
select(max_fd, &readfds, &writefds, NULL, NULL);
printf("after select...\n");
addr_len = sizeof their_addr;
if(FD_ISSET(rv, &readfds))
{
printf("rv is set...\n");
if((numbytes = recvfrom(sockfd, buf, sizeof(buf), 0,
(struct sockaddr *)&their_addr, &addr_len)) == -1) {
perror("recvfrom");
exit(1);
}
} else if(FD_ISSET(rrr, &readfds))
{
printf("rr read is set...\n");
if((numbytes = recvfrom(rtex_rr_sockfd, buf, sizeof(buf), 0,
(struct sockaddr *)&right_addr, &addr_len)) == -1) {
perror("recvfrom");
exit(1);
}
} else if(FD_ISSET(rrw, &writefds))
{
printf("rr write is set...\n");
if((numbytes = sendto(rtex_rw_sockfd, inet_packet.payload, sizeof(inet_packet.payload),
0, p3->ai_addr, p3->ai_addrlen)) == -1) {
perror("sendto rr");
exit(1);
}
}
运行您的程序并在启动后在终端按 Enter 键。它可能会从选择中返回。为什么？因为你唯一告诉 select 听的是 fd 0, stdin！
rvrrrrrwgetaddrinfo()socket()max_fd另外，下次请将代码简化为最小示例。如果您的问题是选择不返回，那么例如。所有处理代码完全无关，一个套接字就足够了，使用
getaddrinfo()getaddrinfo()