c - 打开套接字时出错 : Success

Question

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

void error(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]);
    }
    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, &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 reading from socket");
    }
    printf("%s\n", buffer);
    return 0;
}

当我运行这个程序时，我得到了错误

ERROR opening socket: Success

然后程序什么都不做。另外，我收到警告

 warning: passing argument 2 of ‘connect’ from incompatible pointer type [enabled by default]
 if(connect(sockfd,&serv_addr, sizeof(serv_addr)) < 0)
 ^
In file included from Clientown.c:3:0:
/usr/include/sys/socket.h:138:12: note: expected ‘const struct sockaddr *’ but argument is of type ‘struct sockaddr_in *’
extern int connect (int __fd, __CONST_SOCKADDR_ARG __addr, socklen_t __len);

这是怎么回事？我是 c 的新手，我真的坚持使用这段代码。连接有问题吗？警告重要吗？有人可以帮我解决吗？谢谢。

Answer 1

你在不应该有分号的地方有一个分号:

if (sockfd < 0);
{
    error("ERROR opening socket");
}

因此，error() 函数将始终被调用，即使 if 条件失败。你想要:

if (sockfd < 0)
{
    error("ERROR opening socket");
}