linux socket连接中 ERRNO错误

Connection refused：应该是连接的服务端没有启动或者连接端口错误，可以用如下代码测试

client端：

#include <stdio.h>
#include <sys/types.h>          /* See NOTES */
#include <sys/socket.h>
#include <strings.h>
#include <unistd.h>
#include <netinet/in.h>
#include <string.h>
#include <arpa/inet.h>
#include <errno.h>
#define PORT 1234
#define SERVER "10.1.70.21"

int main()
{
        int fd = socket(AF_INET, SOCK_STREAM, 0);
        int nfd;
        int ret;
        struct sockaddr_in server_addr, client_addr;
        bzero(&server_addr, sizeof(server_addr));

        server_addr.sin_family =AF_INET;
        server_addr.sin_port = htons(PORT);
        inet_pton(AF_INET, SERVER, &server_addr.sin_addr);
        //bind(fd, (struct sockaddr *)&server_addr, sizeof(server_addr));
        errno = 0;
        ret = connect(fd, (struct sockaddr*)&server_addr, sizeof(server_addr));
        if(ret == -1)
        {
                perror("connect: ");
        }
        char buf[1024];
        while(1)
        {
                bzero(buf, 1024);
                ret = read(STDIN_FILENO, buf, sizeof(buf));
                printf("ret: %d, buf: %s", ret, buf);
                ret = write(fd, buf, ret);
                printf("ret:%d
", ret);
                if(ret < 0)
                {
                        perror("write error");
                }
                ret = read(fd, buf, 1024);
                if(ret < 0)
                {
                        perror("ret");
                }
                write(STDOUT_FILENO, buf, ret);
        }
        return 0;
}

 server端：

　　

#include <stdio.h>
#include <sys/types.h>          /* See NOTES */
#include <sys/socket.h>
#include <strings.h>
#include <unistd.h>
#include <netinet/in.h>
#include <string.h>
#include <errno.h>
//server端监听端口
#define PORT 3388
int main()
{
    int fd = socket(AF_INET, SOCK_STREAM, 0);//创建一个socket
    int nfd;
    struct sockaddr_in server_addr, client_addr;
    bzero(&server_addr, sizeof(server_addr));
    server_addr.sin_family =AF_INET; //ipv4
    server_addr.sin_port = htons(PORT);//端口
    server_addr.sin_addr.s_addr = htonl(INADDR_ANY);//监听本主机的所有ip

    bind(fd, (struct sockaddr *)&server_addr, sizeof(server_addr));//绑定
    listen(fd, 30);//监听socket连接，30为三次握手队列大小
    char buf[1024];    
    // 把server_addr.sin_addr的地址转换成字符串（点分十进制表示）
    inet_ntop(AF_INET, &server_addr.sin_addr, buf, sizeof(buf));
    printf("%s
", buf);//一般输出为0.0.0.0
    pid_t pid;    
    while(1)
    {
        bzero(buf, sizeof(buf));//buf清零，相当于memset(buf, 0, sizeof(buf));

        socklen_t len= sizeof(client_addr);
        nfd = accept(fd, (struct sockaddr*)&client_addr, &len);//接收socket连接
        inet_ntop(AF_INET, &client_addr.sin_addr, buf, sizeof(buf));//获取socket连接客户端的ip
        printf("accept connetc %s port %d
", buf, ntohs(client_addr.sin_port));    

        pid = fork();
        //子进程
        if(pid == 0)
        {
            while(1)
            {

                int ret = read(nfd, buf, sizeof(buf));
                if(ret <= 0)
                {
                    perror("ret");
                    return 0;
                }
                write(STDOUT_FILENO, buf, ret);
                write(nfd, buf, ret);
            }
        }
    }
    return 0;
}