Linux上的C套接字编程

Question

我是套接字编程和linux的新手我可以找到一些关于套接字编程的代码我想用这个代码连接到打印机,这段代码使用的是gethostbyname函数,负责获取hostent我觉得一切都很好,除了我还没有主机名我只有一个IP地址(打印机),那么我应该使用什么功能通过IP连接到打印机？

这是代码

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

void error(const char *msg)
{
perror(msg);
exit(0);
}

int main(int argc, char *argv[])
{
int sockfd, portno, n;
struct sockaddr_in serv_addr;
struct hostent *server;

char buffer[256];
if (argc < 3) {
   fprintf(stderr,"usage %s hostname port\n", argv[0]);
   exit(0);
}
portno = atoi(argv[2]);
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd < 0) 
    error("ERROR opening socket");
server = gethostbyname(argv[1]);
if (server == NULL) {
    fprintf(stderr,"ERROR, no such host\n");
    exit(0);
}
bzero((char *) &serv_addr, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
bcopy((char *)server->h_addr, 
     (char *)&serv_addr.sin_addr.s_addr,
     server->h_length);
serv_addr.sin_port = htons(portno);
if (connect(sockfd,(struct sockaddr *) &serv_addr,sizeof(serv_addr)) < 0) 
    error("ERROR connecting");
printf("Please enter the message: ");
bzero(buffer,256);
fgets(buffer,255,stdin);
n = write(sockfd,buffer,strlen(buffer));
if (n < 0) 
     error("ERROR writing to socket");
bzero(buffer,256);
n = read(sockfd,buffer,255);
if (n < 0) 
     error("ERROR reading from socket");
printf("%s\n",buffer);
close(sockfd);
return 0;
}

Answer 1

用getaddrinfo而不是gethostbyname.只要它使用标准表示法,它就应该透明地接受主机名以及IPv4和IPv6地址.

做这样的事情:

int connect_to(char const *host, char const *port)
{
    int sock = -1;
    struct addrinfo hints;
    memset(&hints, 0, sizeof(hints));
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_protocol = IPPROTO_TCP;

    struct addrinfo *servinfo;
    if (getaddrinfo(host, port, &hints, &servinfo) != 0) {
        return sock;
    }

    for (struct addrinfo *serv = servinfo; NULL != serv; serv = serv->ai_next) {
        int tmp = socket(serv->ai_family, serv->ai_socktype, serv->ai_protocol);
        if (tmp == -1) {
            continue;
        }

        if (connect(tmp, serv->ai_addr, serv->ai_addrlen) == -1) {
            close(tmp);
            continue;
        }

        sock = tmp;
        break;
    }

    freeaddrinfo(servinfo);
    return sock;
}