实际上,我的问题非常令人生气。我先给你看一下代码。
/*
** listener.c -- a datagram sockets "server" demo
*/
//Original Code: Brian Hall (beej@beej.us)
//Commented and modified by Vishal Kotcherlakota (PID A07124450)
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#define MYPORT "4960" // the port users will be connecting to
#define YOURPORT "4961"
#define MAXBUFLEN 10000
// get sockaddr, IPv4 or IPv6:
void *get_in_addr(struct sockaddr *sa)
{
//If the socket address struct says it's an IPv4...
if (sa->sa_family == AF_INET) {
//...return the IPv4 variable.
return &(((struct sockaddr_in*)sa)->sin_addr);
}
//otherwise, assume it's IPv6, and get the IPv6 variable
return &(((struct sockaddr_in6*)sa)->sin6_addr);
}
int main(int argc, char *argv[])
{
int sockfd, sockfdAck; //socket file descriptor (handle)
struct addrinfo hints, *servinfo, *p, *q;
int rv;
int numbytes;
unsigned int seqNum, stateNum=0, ackNum;
struct sockaddr_storage their_addr;
struct timeval recvTime, timeStamp, latency;
char buf[MAXBUFLEN], junk[MAXBUFLEN];
size_t addr_len;
char *ackBack;
char s[INET6_ADDRSTRLEN];
if (argc != 2)
{
fprintf(stderr, "usage: <executable> <hostname>\n");
exit(0);
}
memset(&hints, 0, sizeof hints);
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
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(q = servinfo; q != NULL; q = q->ai_next) {
if ((sockfd = socket(q->ai_family, q->ai_socktype,
q->ai_protocol)) == -1) {
perror("listener: socket");
continue;
}
if (bind(sockfd, q->ai_addr, q->ai_addrlen) == -1) {
close(sockfd);
perror("listener: bind");
continue;
}
break;
}
if (q == NULL) {
fprintf(stderr, "listener: failed to bind socket\n");
return 2;
}
freeaddrinfo(servinfo);
memset(&hints, 0, sizeof hints);
hints.ai_family = AF_UNSPEC; // set to AF_INET to force IPv4
hints.ai_socktype = SOCK_DGRAM;
if ((rv = getaddrinfo(argv[1], BACKPORT, &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 ((sockfdAck = socket(p->ai_family, p->ai_socktype,
p->ai_protocol)) == -1) {
perror("listener: socket");
continue;
}
break;
}
if (p == NULL) {
fprintf(stderr, "listener: failed to bind socket\n");
return 2;
}
freeaddrinfo(servinfo);
printf("listener: waiting to recvfrom...\n");
while (1)
{
addr_len = sizeof their_addr;
if ((numbytes = recvfrom(sockfd, buf, MAXBUFLEN-1 , 0,
(struct sockaddr *)&their_addr, &addr_len)) == -1) {
perror("recvfrom");
exit(1);
}
/*printf("listener: got packet from %s\n",
inet_ntop(their_addr.ss_family,
get_in_addr((struct sockaddr *)&their_addr),
s, sizeof s));
printf("listener: packet is %d bytes long\n", numbytes);
*/
buf[numbytes] = '\0';
sscanf(buf,"%u %s",&seqNum, junk);
if (seqNum == stateNum + 1)
{
stateNum = seqNum;
printf("Ok, state is now %u.\n", stateNum);
}
ackBack = malloc(20*sizeof(char));
sprintf(ackBack, "%u acknowledged\0", stateNum);
numbytes = sendto(sockfdAck, ackBack, strlen(ackBack), 0, p->ai_addr, p->ai_addrlen);
if (numbytes == -1);
{
perror("sendto");
exit(1);
}
free(ackBack);
}
return 0;
}
请原谅邋code的代码;我拼命想按时完成这项任务。目标是使用数据报套接字开发ARQ协议。这段代码应该可行,但是当我运行它时,我收到错误sendto: Success
,这意味着我的sendto()
调用失败了。我无法在任何地方找到这方面的文件,而且我非常绝望。
答案 0 :(得分:6)
它与bind()
无关 - 事实上看一下这个语法:
if (numbytes == -1) ; // semicolon !
{
perror("sendto");
exit(1);
}
你有一个没有身体的条件,然后是没有条件的身体,它总是执行(你可以观察到)。
添加numbytes的printf,您将看到它设置正确,没有错误。
为了避免这种难以看清的错误,我通常会在条件之后立即放置开口支架 - 然后你会立即发现它。但当然这是公司/项目编码惯例的问题。