下列测试是在两台机器上（服务端和客户端），编译运行
1. # gcc client.c -o client
client.c: 在函数‘main’中:
client.c:12: 错误：‘dest_addr’的存储大小未知
解决方案：
# gcc -E client.c | grep "struct sockaddr_in"
struct sockaddr_in dest_addr;
首先预处理编译client.c，发现无头文件，说明头文件指定错误
实际struct sockaddr_in声明包含在下列头文件中
#include <arpa/inet.h>
#include <netinet/in.h>
2. # gcc client.c -o client
#客户端
# ./client
write error: Connection refused
send number:9
服务器端
#tcpdump -i eth0 host 192.168.60.136 and udp
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
16:49:38.927885 IP localhost.56296 > abc123.ndmp: UDP, length 1024
16:49:38.927940 IP localhost.56296 > abc123.ndmp: UDP, length 1024
16:49:38.927958 IP localhost.56296 > abc123.ndmp: UDP, length 1024
16:49:38.927973 IP localhost.56296 > abc123.ndmp: UDP, length 1024
16:49:38.927988 IP localhost.56296 > abc123.ndmp: UDP, length 1024
16:49:38.928005 IP localhost.56296 > abc123.ndmp: UDP, length 1024
16:49:38.928021 IP localhost.56296 > abc123.ndmp: UDP, length 1024
16:49:38.928028 IP localhost.56296 > abc123.ndmp: UDP, length 1024
上述没有运行server端，直接运行client端，可见系统发送一部分数据包。服务器端接收数据包
3.服务器端
# netstat -su
IcmpMsg:
InType3: 55
OutType3: 467
Udp:
9617286 packets received
375854 packets to unknown port received.
108733 packet receive errors
6663 packets sent
RcvbufErrors: 108733
UdpLite:
IpExt:
InMcastPkts: 12125
OutMcastPkts: 209
InBcastPkts: 24214
OutBcastPkts: 18
InOctets: 15042525827
OutOctets: 108912059
InMcastOctets: 2415162
OutMcastOctets: 21128
InBcastOctets: 3161452
OutBcastOctets: 1404
#./server &
# netstat -su
IcmpMsg:
InType3: 55
OutType3: 467
Udp:
9624946 packets received
375854 packets to unknown port received.
111096 packet receive errors
6677 packets sent
RcvbufErrors: 111096
UdpLite:
IpExt:
InMcastPkts: 12139
OutMcastPkts: 209
InBcastPkts: 24261
OutBcastPkts: 18
InOctets: 15058618880
OutOctets: 109265743
InMcastOctets: 2417401
OutMcastOctets: 21128
InBcastOctets: 3165284
OutBcastOctets: 1404
###########################
192.168.60.136,7637
#./client
./client
send number:10000
上述系统发生丢包现象， 发送10000，实际接受了7637,从而由此可见udp不可靠的，需要进行流量控制。
上述大部分内容，参考了<<Unix 网络编程>>
================================================================client.c
//#include <arpa/inet.h>
//#include <netinet/in.h>
#include <sys/types.h> /* See NOTES */
#include <sys/socket.h>
#include <stdio.h>
#include <strings.h>
int main()
{
char buf[1024];
int i=0;
struct sockaddr_in dest_addr;
int sockfd = socket(AF_INET,SOCK_DGRAM,0);
int len = sizeof(buf);
bzero(&dest_addr,sizeof(dest_addr));
dest_addr.sin_family=AF_INET;
dest_addr.sin_port=htons(10000);
dest_addr.sin_addr.s_addr=inet_addr("192.168.60.123");
connect(sockfd,(struct sockaddr *)&dest_addr, sizeof(dest_addr));
while(i<10000)
{
i++;
int ret = sendto(sockfd, buf, len, 0, (struct sockaddr *)&dest_addr, sizeof(dest_addr));
if (ret < 0)
{
perror("write error");
break;
}
}
printf("send number:%d\n",i);
}
=======================================================================server.c
#include <arpa/inet.h>
#include <netinet/in.h>
int main()
{
char buf[1024];
int i=0;
int fd = socket(AF_INET,SOCK_DGRAM,0);
struct sockaddr_in dest_addr;
bzero(&dest_addr,sizeof(dest_addr));
socklen_t addrlen;
dest_addr.sin_family=AF_INET;
dest_addr.sin_port=htons(10000);
dest_addr.sin_addr.s_addr=INADDR_ANY;
bind(fd,(struct sockaddr*)&dest_addr,sizeof(dest_addr));
while (1)
{
i++;
int ret = recvfrom(fd, buf, 1024, 0,(struct sockaddr*) &dest_addr, &addrlen);
if(ret < 0)
{
perror("recvfrom");
break;
}
printf ("%s,%d\n", inet_ntoa (dest_addr.sin_addr), i);
}
printf ("%s,%d\n", inet_ntoa (dest_addr.sin_addr), i);
}