LinuxC，流式套接字，客户端能连接上服务器端，但是彼此收不到对方发出的数据，急急急！
服务器端代码：

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <stdio.h>
#include <stdlib.h>
#include<sys/types.h>
#include<sys/socket.h>
#include<pthread.h>
#include<unistd.h>
#include<errno.h>
#include<netdb.h>
#include<string.h>


int main(int argc, char *argv[])
{
    int sockfd, new_fd;
    struct sockaddr_in server_addr;
    struct sockaddr_in client_addr;
    int sin_size, portnumber;
    char reply[]="收到数据!";
    char recv_buf[1024]; 
    int nbytes; 
 
    if(argc != 2)
    {
        fprintf(stderr, "Usage:%s portnumber\a\n", argv[0]);
        exit(1);
    }
     
    if((portnumber = atoi(argv[1])) < 0)
    {
         fprintf(stderr, "Usage:%s portnumber\a\n", argv[0]);
         exit(1);
    }

    /*服务器端开始建立socket描述符*/
    if((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == 1)
    {
        fprintf(stderr, "socket error:%s portnumber\a\n", strerror(errno));
        exit(1);
    }
    
    /*服务器端填充sockaddr结构*/
    bzero(&server_addr, sizeof(struct sockaddr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    server_addr.sin_port = htons(portnumber);
    /*捆绑sockfd描述符*/
    if(bind(sockfd, (struct sockaddr *)(&server_addr), sizeof(struct sockaddr)) == -1)
    {
        fprintf(stderr, "Bind error:%s\n\a", strerror(errno));
        exit(1);
    }
    /*监听sockfd描述符号*/
    if(listen(sockfd, 5) == -1)
    {
fprintf(stderr, "Listen error:%s\n\a", strerror(errno));
exit(1);
    }
    printf("服务器进程已开启...\n");    

    while(1)
    {
    /*服务器阻塞，直到客户端程序建立连接*/
    sin_size;
    if((new_fd = accept(sockfd, (struct sockaddr *)(&client_addr), &sin_size)) == -1)
    {
    fprintf(stderr, "Accept error:%s\n\a", strerror(errno));
    exit(1);
    }
    printf("Server get connection from %s\n", inet_ntoa(client_addr.sin_addr));

            if(nbytes = recv(new_fd, recv_buf, 1024, 0) == -1)
            {
                fprintf(stderr, "Read Error:%s\n\a", strerror(errno));
                exit(1);
            }
            recv_buf[nbytes] = '\0';
            printf("Recvived %s data:%s\n", inet_ntoa(client_addr.sin_addr), recv_buf);

    if(send(new_fd, reply, strlen(reply), 0) == -1)
    {
    fprintf(stderr, "Write Error:%s\n", strerror(errno));
    exit(1);
    }
    //puts(reply);
            //printf("%d\n", send_num);
    /*这个通信已经结束*/
    close(new_fd);
    }
    close(sockfd);

    return EXIT_SUCCESS;
}

客户端代码：

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

int main(int argc, char *argv[])
{
    int sockfd;
    char send_buf[1024], recv_buf[100];  
 
    struct sockaddr_in server_addr;
    struct hostent *hostl;
    int portnumber, nbytes;
 
    if(argc != 3)
    {
        fprintf(stderr, "Usage:%s portnumber\a\n", argv[0]);
        exit(1);
    }
     
    if((portnumber = atoi(argv[2])) < 0)
    {
         fprintf(stderr, "Usage:%s portnumber\a\n", argv[0]);
         exit(1);
    }
 
    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(portnumber);
    server_addr.sin_addr.s_addr = inet_addr(argv[1]);
    
    if((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == 1)
    {
        fprintf(stderr, "Socket error:%s\a\n", strerror(errno));
        exit(1);
    }
    /*客户程序发起的连接请求*/
    if(connect(sockfd, (struct sockaddr*)(&server_addr), sizeof(server_addr)) == -1)
    {
        fprintf(stderr, "connect error:%s\n\a", strerror(errno));
        exit(1);
    }
    //连接成功
    scanf("%s", &send_buf);
    if(send(sockfd, send_buf, strlen(send_buf), 0) == -1)
    {
fprintf(stderr, "Write Error:%s\n", strerror(errno));
exit(1);
    }
    if(nbytes = recv(sockfd, recv_buf, 100, 0) == -1)
    {
         fprintf(stderr, "Read Error:%s\n\a", strerror(errno));
         exit(1);
    }
    printf("%d\n",nbytes);
    recv_buf[nbytes] = '\0';
    printf("Data from the server:%s\n", recv_buf);

    /*结束通信*/
    close(sockfd);

    return EXIT_SUCCESS;
}

[解决办法]
你的运算符优先级搞错了！！！
= 的优先级低于 ==
所以下面的if有问题：
if(nbytes = recv(sockfd, recv_buf, 100, 0) == -1)
{
fprintf(stderr, "Read Error:%s\n\a", strerror(errno));
exit(1);
}

应该为：
if ((nbytes = recv(...)) == -1)
{
...
}