#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include "wrap.h"

int main()
{
        //建立套接字
        int serv_sock = Socket(AF_INET,SOCK_STREAM,0);
        //將套接字與IP,PORT繫結

        //建立sokaddr_in結構體，並經行本地位元組序和網路位元組序的轉換
 

        struct sockaddr_in serv_addr;
        memset(&serv_addr,0,sizeof(serv_addr));
        serv_addr.sin_family = AF_INET;
        serv_addr.sin_addr.s_addr=Inet_addr("127.0.0.1");
        serv_addr.sin_port = Htons(1234);

        Bind(serv_sock,(struct sockaddr*)&serv_addr,sizeof(serv_addr));

        //進入監聽狀態，等待使用者發起請求
 

        listen(serv_sock,20);

        //接收客戶端請求
        struct sockaddr_in clnt_addr;
        socklen_t clnt_addr_size =sizeof(clnt_addr);
        int clnt_sock;
        int pid;
        while((clnt_sock=Accept(serv_sock,(struct sockaddr *)&clnt_addr,&clnt_addr_size)) !=0)
        {
                pid=fork();
                if
 
(pid==-1)
                {
                        perror("fork err");
                        exit(1);
                }
                if(pid==0)
                {
                        char buf[4096];
                        int n,i;
                        while((n=read(clnt_sock,buf,sizeof(buf))) != 0)
                        {
                                for(i=0;i<n;i++)
                                {
                                        buf[i]=toupper(buf[i]);
                                }
                                write(clnt_sock,buf,n);
                        }
                        //關閉套接字
                        close(clnt_sock);
                        exit(2);
                }
                else
                {
                        //關閉套接字
                        close(clnt_sock);
                }
        }



        close(serv_sock);
        return 0;





}

第二個例子

/* For sockaddr_in */
#include <netinet/in.h>
/* For socket functions */
#include <sys/socket.h>

#include <unistd.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>

#define MAX_LINE 16384

char
rot13_char(char c)
{
    /* We don't want to use isalpha here; setting the locale would change
     * which characters are considered alphabetical. */
    if ((c >= 'a' && c <= 'm') || (c >= 'A' && c <= 'M'))
        return c + 13;
    else if ((c >= 'n' && c <= 'z') || (c >= 'N' && c <= 'Z'))
        return c - 13;
    else
        return c;
}

void
child(int fd)
{
    char outbuf[MAX_LINE+1];
    size_t outbuf_used = 0;
    ssize_t result;

    while (1) {
        char ch;
        result = recv(fd, &ch, 1, 0);
        if (result == 0) {
            break;
        } else if (result == -1) {
            perror("read");
            break;
        }

        /* We do this test to keep the user from overflowing the buffer. */
        if (outbuf_used < sizeof(outbuf)) {
            outbuf[outbuf_used++] = rot13_char(ch);
        }

        if (ch == '\n') {
            send(fd, outbuf, outbuf_used, 0);
            outbuf_used = 0;
            continue;
        }
    }
}

void
run(void)
{
    int listener;
    struct sockaddr_in sin;

    sin.sin_family = AF_INET;
    sin.sin_addr.s_addr = 0;
    sin.sin_port = htons(40713);

    listener = socket(AF_INET, SOCK_STREAM, 0);

#ifndef WIN32
    {
        int one = 1;
        setsockopt(listener, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
    }
#endif

    if (bind(listener, (struct sockaddr*)&sin, sizeof(sin)) < 0) {
        perror("bind");
        return;
    }

    if (listen(listener, 16)<0) {
        perror("listen");
        return;
    }



    while (1) {
        struct sockaddr_storage ss;
        socklen_t slen = sizeof(ss);
        int fd = accept(listener, (struct sockaddr*)&ss, &slen);
        if (fd < 0) {
            perror("accept");
        } else {
            if (fork() == 0) {
                child(fd);
                exit(0);
            }
        }
    }
}

int
main(int c, char **v)
{
    run();
    return 0;
}