C语言 socket编程实例

一. 面向连接的流式套接字 C/S 例子

在树莓派下，新建一个 Server1.c，命令 nano Server1.c，然后写入如下内容

#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 <netdb.h> 
#include <arpa/inet.h> 
#include <sys/wait.h> 
#include <signal.h> 
#define PORT "9090" // the port users will be connecting to 
#define BACKLOG 10 
// how many pending connections queue will hold 
void sigchld_handler(int s) 
{ 
	while(waitpid(-1, NULL, WNOHANG) > 0); 
}
// 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) 
{ 
    int sockfd, new_fd; // listen on sock_fd, new connection on new_fd 
    struct addrinfo hints, *servinfo, *p; 
    struct sockaddr_storage their_addr; // connector's address information 
    socklen_t sin_size; 
    struct sigaction sa; 
    int yes=1;
    char s[INET6_ADDRSTRLEN]; 
    int rv; 
    memset(&hints, 0, sizeof hints); 
    hints.ai_family = AF_UNSPEC; 
    hints.ai_socktype = SOCK_STREAM; 
    hints.ai_flags = AI_PASSIVE; // use my IP 
    if ((rv = getaddrinfo(NULL, PORT, &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("server: socket"); 
        continue; 
    }
    if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &yes, 
    sizeof(int)) == -1) { 
        perror("setsockopt"); 
        exit(1); 
    }
    if (bind(sockfd, p->ai_addr, p->ai_addrlen) == -1) { 
        close(sockfd); 
        perror("server: bind"); 
        continue; 
    }
    break; 
}
    if (p == NULL) { 
        fprintf(stderr, "server: failed to bind\n"); 
        return 2; 
    }
    freeaddrinfo(servinfo); // all done with this structure 
    if (listen(sockfd, BACKLOG) == -1) { 
        perror("listen"); 
        exit(1); 
    }
    sa.sa_handler = sigchld_handler; // reap all dead processes 
    sigemptyset(&sa.sa_mask); 
    sa.sa_flags = SA_RESTART; 
    if (sigaction(SIGCHLD, &sa, NULL) == -1) { 
        perror("sigaction"); 
        exit(1); 
    }
    printf("server: waiting for connections...\n"); 
    while(1) { // main accept() loop 
        sin_size = sizeof their_addr; 
        new_fd = accept(sockfd, (struct sockaddr *)&their_addr, &sin_size); 
        if (new_fd == -1) { 
            perror("accept"); 
            continue; 
        }
        inet_ntop(their_addr.ss_family, 
        get_in_addr((struct sockaddr *)&their_addr), 
        s, sizeof s); 
        printf("server: got connection from %s\n", s); 
        if (!fork()) { // this is the child process 
            close(sockfd); // child doesn't need the listener 
            if (send(new_fd, "Hello, world!", 13, 0) == -1) 
            perror("send"); 
            close(new_fd); 
            exit(0); 
        }
        close(new_fd); // parent doesn't need this 
    }
    return 0; 
}

然后编译并运行

gcc Server1.c -o Server1
./Server1

在Ubuntu系统下，新建一个Client1.c文件，命令gedit Client1.c，然后写入如下内容

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <netdb.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <arpa/inet.h>

#define PORT "9090"  //the port client will be connecting to
#define MAXDATASIZE 100  //max number of bytes we can get at once

//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(int argc, char *argv[])
{
	int sockfd, numbytes;
	char buf[MAXDATASIZE];
	struct addrinfo hints, *servinfo, *p;
	int rv;
	char s[INET6_ADDRSTRLEN];
	if(argc != 2)
	{
		fprintf(stderr, "usage:client hostname\n");
		exit(1);
	}
	memset(&hints, 0, sizeof hints);
	hints.ai_family = AF_UNSPEC;
	hints.ai_socktype = SOCK_STREAM;
	if((rv = getaddrinfo(argv[1], PORT, &hints, &servinfo)) != 0)
	{
		fprintf(stderr, "getaddrinfo:%s\n",gai_strerror(rv));
		return 1;
	}
    // loop through all the results and connect 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("client:socket");
			continue;
		}
		if(connect(sockfd, p->ai_addr, p->ai_addrlen) == -1)
		{
			close(sockfd);
			perror("client:connect");
			continue;
		}
		break;
	}
	if(p == NULL)
	{
		fprintf(stderr, "client:failed to connect\n");
		return 2;
	}
	inet_ntop(p->ai_family, get_in_addr((struct sockaddr*)p->ai_addr), s, sizeof s);
	printf("client:connecting to %s\n",s);
	freeaddrinfo(servinfo);// all done with this structure 
	if((numbytes = recv(sockfd, buf, MAXDATASIZE-1, 0)) == -1)
	{
		perror("recv");
		exit(1);
	}
	buf[numbytes] = '\0';
	printf("client:received %s\n",buf);
	close(sockfd);
	return 0;
}

gcc Client1.c -o Client1
./Client1 192.168.43.161
# 二级目录

二. 非阻塞的多人聊天服务器端例子

在树莓派下，新建一个Server2.c文件，命令nano Server2.c，然后写入如下内容

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>

#define PORT "9090"  //port we're listening on

//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)
{
    fd_set master; 
    // master file descriptor list 
    fd_set read_fds; // temp file descriptor list for select() 
    int fdmax; 
    // maximum file descriptor number
    int listener; 
    // listening socket descriptor 
    int newfd; 
    // newly accept()ed socket descriptor 
    struct sockaddr_storage remoteaddr; // client address 
    socklen_t addrlen; 
    char buf[256]; 
    // buffer for client data 
    int nbytes; 
    char remoteIP[INET6_ADDRSTRLEN]; 
    int yes=1; 
    // for setsockopt() SO_REUSEADDR, below 
    int i, j, rv; 
    struct addrinfo hints, *ai, *p; 
    FD_ZERO(&master); 
    // clear the master and temp sets 
    FD_ZERO(&read_fds); 
    // get us a socket and bind it 
    memset(&hints, 0, sizeof hints); 
    hints.ai_family = AF_UNSPEC; 
    hints.ai_socktype = SOCK_STREAM; 
    hints.ai_flags = AI_PASSIVE; 
    if((rv = getaddrinfo(NULL, PORT, &hints, &ai)) != 0)
    {
        fprintf(stderr, "selectserver:%s\n", gai_strerror(rv));
        exit(1);
    }

    for(p = ai; p != NULL; p = p->ai_next)
    {
        listener = socket(p->ai_family, p->ai_socktype, p->ai_protocol);
        if(listener < 0)
        {
            continue;
        }
        // lose the pesky "address already in use" error message 
        setsockopt(listener, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int));
        if(bind(listener, p->ai_addr, p->ai_addrlen) < 0)
        {
            close(listener);
            continue;
        }
        break;
    }
	// if we got here, it means we didn't get bound 
    if(p == NULL)
    {
        fprintf(stderr, "selectserver:failed to bind\n");
        exit(2);
    }

    freeaddrinfo(ai);  // all done with this 
    // listen
    if(listen(listener, 10) == -1)
    {
        perror("listen");
        exit(3);
    }
    // add the listener to the master set 
    FD_SET(listener, &master);
	// keep track of the biggest file descriptor 
    fdmax = listener;  // so far, it's this one 
	// main loop 
    for(;;)
    {
        read_fds = master; // copy it 
        if(select(fdmax + 1, &read_fds, NULL, NULL, NULL) == -1)
        {
            perror("select");
            exit(4);
        }
		// run through the existing connections looking for data to read 
        for(i = 0; i <= fdmax; i++)
        {
            if(FD_ISSET(i, &read_fds))// we got one!!
            {
                if(i == listener)
                {
                    // handle new connections
                    addrlen = sizeof remoteaddr;
                    newfd = accept(listener, (struct sockaddr *)&remoteaddr, &addrlen);

                    if(newfd == -1)
                    {
                        perror("accept");
                    }
                    else
                    {
                        FD_SET(newfd, &master); // add to master set 
                        if(newfd > fdmax)
                        {
                            // keep track of the max 
                            fdmax = newfd;
                        }
                        printf("selectserver: new connection from %s on " 
                        "socket %d\n", 
                        inet_ntop(remoteaddr.ss_family, 
                        get_in_addr((struct sockaddr*)&remoteaddr), 
                        remoteIP, INET6_ADDRSTRLEN), 
                        newfd); 
                    }
                }
                else
                {
                    // handle data from a client 
                    if((nbytes = recv(i, buf, sizeof buf, 0)) <= 0)
                    {
                        // got error or connection closed by client 
                        if(nbytes == 0)
                        {
                            // connection closed 
                            printf("selectserver:socket %d hung up\n", i);
                        }
                        else
                        {
                            perror("recv");
                        }
                        close(i);// bye! 
                        FD_CLR(i, &master);// remove from master set 
                    }
                    else
                    {
                        // we got some data from a client 
                        for(j =0; j <= fdmax; j++)
                        {
			    			// send to everyone! 
                            if(FD_ISSET(j, &master))
                            {
                                 // except the listener and ourselves 
                                if(j != listener && j != i)
                                {
                                    if(send(j, buf, nbytes, 0) == -1)
                                    {
                                        perror("send");
                                    }
                                }
                            }
                        }
                    }
                }  //END handle from client
            }  //END got new incoming connection
        }  //END looping through file descriptors
    }  //END for(;;)--and you thought it would never end!
    return 0;
}

gcc Server2.c -o Server2
./Server2

在Ubuntu下新建一个Client2.c文件，命令gedit Client2.c，然后写入如下内容

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <netdb.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <arpa/inet.h>

#define PORT "9090"  //the port client will be connecting to
#define MAXDATASIZE 100  //max number of bytes we can get at once

int sockfd, numbytes;
char buf[MAXDATASIZE];

//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);
}

void *recvMag()
{
    while(1)
    {
        if((numbytes = recv(sockfd, buf, MAXDATASIZE-1, 0)) == -1)
	{
		perror("recv");
		exit(1);
	}
	if(numbytes == 1)
		continue;
	buf[numbytes] = '\0';
	printf("\nreceived：%s\n",buf);
    }
}

int main(int argc, char *argv[])
{
	//int sockfd, numbytes;
	//char buf[MAXDATASIZE];
	struct addrinfo hints, *servinfo, *p;
	int rv;
	char s[INET6_ADDRSTRLEN];
	pthread_t t1;
    char mag[MAXDATASIZE];
    
	if(argc != 2)
	{
		fprintf(stderr, "usage:client hostname\n");
		exit(1);
	}
	memset(&hints, 0, sizeof hints);
	hints.ai_family = AF_UNSPEC;
	hints.ai_socktype = SOCK_STREAM;
	if((rv = getaddrinfo(argv[1], PORT, &hints, &servinfo)) != 0)
	{
		fprintf(stderr, "getaddrinfo:%s\n",gai_strerror(rv));
		return 1;
	}
    // loop through all the results and connect 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("client:socket");
			continue;
		}
		if(connect(sockfd, p->ai_addr, p->ai_addrlen) == -1)
		{
			close(sockfd);
			perror("client:connect");
			continue;
		}
		break;
	}
	if(p == NULL)
	{
		fprintf(stderr, "client:failed to connect\n");
		return 2;
	}
	inet_ntop(p->ai_family, get_in_addr((struct sockaddr*)p->ai_addr), s, sizeof s);
	printf("client:connecting to %s\n",s);
	freeaddrinfo(servinfo);// all done with this structure 
	
	int err = pthread_create(&t1, NULL, recvMag, NULL);
	if(err != 0)
	{
		printf("receive failed");
		exit(1);
	}
    
	while(1)
	{
        scanf("%s", mag);
        if(send(sockfd, mag, sizeof mag, 0) == -1)
        {
            printf("send failed!\n");
        }
	}
	return 0;
}

编译并运行

gcc -pthread Client2.c -o Client2
./Client2 192.168.43.161

三. 简单的 IPv6 UDP socket编程

在树莓派和Ubuntu下查看自己的IPv6地址地址，ifconfig，然后再看双方能不能ping通
在树莓派下新建一个Server4.c文件，命令nano Server4.c，然后写入如下内容

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <sys/wait.h>
#include <unistd.h>
#include <arpa/inet.h>
 
int main(int argc, char **argv)
{
	struct sockaddr_in6 s_addr;
	struct sockaddr_in6 c_addr;
	int sock;
	socklen_t addr_len;
	int len;
	char buff[128];
	char buf_ip[128];
 
	if ((sock = socket(AF_INET6, SOCK_DGRAM, 0)) == -1) {
		perror("socket");
		exit(errno);
	} else
		printf("create socket.\n\r");
 
	memset(&s_addr, 0, sizeof(struct sockaddr_in6));
	s_addr.sin6_family = AF_INET6;
 
	if (argv[2])
		s_addr.sin6_port = htons(atoi(argv[2]));
	else
		s_addr.sin6_port = htons(4444);
 
	if (argv[1])
		inet_pton(AF_INET6, argv[1], &s_addr.sin6_addr);
	else
		s_addr.sin6_addr = in6addr_any;
 
	if ((bind(sock, (struct sockaddr *) &s_addr, sizeof(s_addr))) == -1) {
		perror("bind");
		exit(errno);
	} else
		printf("bind address to socket.\n\r");
 
	addr_len = sizeof(c_addr);
	while (1) {
		len = recvfrom(sock, buff, sizeof(buff) - 1, 0,
					   (struct sockaddr *) &c_addr, &addr_len);
		if (len < 0) {
			perror("recvfrom");
			exit(errno);
		}
 
		buff[len] = '\0';
		printf("receive from %s: buffer:%s\n\r",
				inet_ntop(AF_INET6, &c_addr.sin6_addr, buf_ip, sizeof(buf_ip)), 
				buff);
	}
	return 0;
}

编译运行

gcc Server4.c -o server4
./server4 2409:8960:1e48:f1a:b6a4:81d5:7021:4873 9090

再Ubuntu下，新建一个Client4.c文件，然后写入如下内容

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <sys/wait.h>
#include <unistd.h>
#include <arpa/inet.h>
 
int main(int argc, char **argv)
{
	struct sockaddr_in6 s_addr;
	int sock;
	int addr_len;
	int len;
	char buff[128];
 
	if ((sock = socket(AF_INET6, SOCK_DGRAM, 0)) == -1) {
		perror("socket");
		exit(errno);
	} else
		printf("create socket.\n\r");
 
	s_addr.sin6_family = AF_INET6;
	if (argv[2])
		s_addr.sin6_port = htons(atoi(argv[2]));
	else
		s_addr.sin6_port = htons(4444);
 
	if (argv[1])
		inet_pton(AF_INET6, argv[1], &s_addr.sin6_addr);
	else {
		printf("usage:./command ip port\n");
		exit(0);
	}
 
	addr_len = sizeof(s_addr);
	strcpy(buff, "hello i'm here");
	len = sendto(sock, buff, strlen(buff), 0,
				 (struct sockaddr *) &s_addr, addr_len);
	if (len < 0) {
		printf("\n\rsend error.\n\r");
		return 3;
	}
 
	printf("send success.\n\r");
	return 0;
}

编译运行

gcc Client4.c -o Client4
./Client4 2409:8960:1e48:f1a:b6a4:81d5:7021:4873 9090