并發服務器就是能夠同時處理多個客戶端請求的服務器。并發服務器可通過多進程或者多線程程序來實現，這里采用多進程程序。

服務器

#include<stdio.h>

include<stdlib.h>
include<string.h>
include<unistd.h>
include<sys/types.h>
include<sys/socket.h>
include<netinet/in.h>/定義了struct sockaddr_in/
void main()
{
    int sockfd;
    /創建socket/
    sockfd=socket(AF_INET,SOCK_STREAM,0);
    if(sockfd==-1)
    {
        printf("create socket false");
        exit(1);

    }
    /綁定地址/
    struct sockaddr_in server_addr;
    server_addr.sin_family=AF_INET;
    server_addr.sin_port=htons(5000);
    server_addr.sin_addr.s_addr=htonl(INADDR_ANY);
    if(bind(sockfd,(const struct sockaddr )(&server_addr),sizeof(server_addr))==-1)
    {
        printf("bind false");
        exit(1);

    }
    /監聽端口/
    listen(sockfd,3);
    /父進程等待連接，成功連接后創建子進程收發數據/
    int newfd;
    struct sockaddr_in client_addr;
    int addrlen=sizeof(client_addr);
    char buf[128];
    pid_t pid;
    while(1)
    {
        newfd=accept(sockfd,(struct sockaddr )(&client_addr),&addrlen);
        pid=fork();
        if(pid==0)
        {
            while(1)
            {
                recv(newfd,buf,128,0);
                printf("the message is from :%s\n",inet_ntoa(client_addr.sin_addr));
                printf("the message received is %s\n",buf);
                if(strcmp(buf,"exit")==0)
                {
                    break;

                }

        }
        close(newfd);
        close(sockfd);
        exit(0);
    }
}
/*結束連接*/
close(newfd);
close(sockfd);

}</pre> 


 客戶端 

#include<stdio.h>

include<stdlib.h>
include<string.h>
include<unistd.h>
include<sys/types.h>
include<sys/socket.h>
include<netinet/in.h>/定義了struct sockaddr_in/
void main()
{
    /創建socket/
    int sockfd=socket(AF_INET,SOCK_STREAM,0);
    if(sockfd==-1)
    {
        printf("create socket false");
        exit(1);

    }
    /連接服務器/
    struct sockaddr_in server_addr;
    server_addr.sin_family=AF_INET;
    server_addr.sin_port=htons(5000);
    server_addr.sin_addr.s_addr=inet_addr("192.168.137.246");
    if(connect(sockfd,(const struct sockaddr )(&server_addr),sizeof(server_addr))==-1)
    {
        printf("connect false");
        exit(1);

    }
    /收發數據/
    printf("please enter your message,and exit for exit\n");
    char buf[128];
    while(1)
    {
        scanf("%s",buf);
        send(sockfd,buf,128,0);
        if(strcmp(buf,"exit")==0)
            break;
    }
    /結束連接*/
    close(sockfd);
}</pre> 

 來自：http://blog.csdn.net/u011012049/article/details/47452669