如题所示，用标准C语言编写一个ftp协议上传文件的简单程序，请各位大虾指导，谢谢。

see busybox ftp.c or libwww  HTFTP.c

有例子吗？请发到我的邮箱[email]149021503@[/email]
谢谢

完全不懂怎么写,估计高手贴出来也看不明白了我...悲剧..有大虾贴出来的话建议也给我发个,最好带N-S或伪代码的.并在程序里注解下,谢谢了.C语言学了这么久了,没写出过有价值的东西..

学会用socket接口，理解FTP协议就可以编程了。网络编程难在要去学很多协议，可以从编写局域网传输文件或聊天软件开始。

是啊,很困难,但是只有困难才有意思啊.羡慕黑客,不如自己漫漫学习写程序,有一天你会觉得写程序很简单很好玩啊

没有想象中的那么难。给个TCP协议传输数据的例子看看：

服务器端：

#include <stdio.h>
#include <winsock2.h>
#include <time.h>
#pragma  comment(lib,"ws2_32.lib ")

#define        SERVER_PORT        6666
#define        BUFFERLEN        128

int main()
{
    WORD    wVersionRequested;
    WSADATA    wsadata;
    int ret, nLength,length;
    SOCKET    sListen, sServer;

    struct sockaddr_in  saServer,saClient;

    char tmpbuf[BUFFERLEN];
    char    *ptr;

    //winsock初始化
    wVersionRequested = MAKEWORD(2,2);
    ret = WSAStartup(wVersionRequested,&wsadata);
    if(ret != 0)
    {
        printf("WSAStartup() failed \n");
        return 1;
    }

    //确认Winsock DLL支持2.2版本
    if(LOBYTE(wsadata.wVersion) != 2 || HIBYTE(wsadata.wVersion) != 2)
    {
        WSACleanup();
        printf("Invalid winsock version \n");
        return 2;
    }

    //创建Socket 使用TCP协议
    sListen = socket(AF_INET,SOCK_STREAM,IPPROTO_TCP);
    if(sListen == INVALID_SOCKET)
    {
        WSACleanup();
        printf("socket failed \n");
        return 3;
    }

    //构建本地地址信息
    saServer.sin_family = AF_INET;
    saServer.sin_port = htons(SERVER_PORT);
    saServer.sin_addr.S_un.S_addr = htonl(INADDR_ANY);

    //绑定
    ret = bind(sListen,(struct sockaddr *)&saServer,sizeof(saServer));
    if( ret == SOCKET_ERROR)
    {
        printf("bind() failed! error code: %d\n \n",WSAGetLastError());
        closesocket(sListen);
        WSACleanup();        
        return 4;
    }

    //侦听连接请求
    ret = listen(sListen,5);
    if( ret == SOCKET_ERROR)
    {
        printf("listem() failed! error code: %d\n \n",WSAGetLastError());
        closesocket(sListen);
        WSACleanup();        
        return 5;
    }

    printf("Waiting for client connecting !\n");
    printf("Ctrl + C to quit \n");

    //阻塞等待接受客户端连接
    length = sizeof(saClient);
    sServer = accept(sListen,(struct sockaddr *)&saClient, &length);

    if(sServer == INVALID_SOCKET)
    {
        printf("accept() failed! error code : %d\n",WSAGetLastError());
        closesocket(sListen);
        WSACleanup();        
        return 6;
    }

    printf("Accepted client: %s:%d\n",
        inet_ntoa(saClient.sin_addr),ntohs(saClient.sin_port));

    while(1)
    {
        _strtime( tmpbuf );
        //给客户端发送的数据
        nLength = strlen(tmpbuf);
    
        ptr = tmpbuf;


        //发送数据
        ret = send(sServer,ptr,nLength+1,0);
        if(ret == SOCKET_ERROR)
        {        
            printf("send() failederror code : %d\n",WSAGetLastError());    
            break;
        }
        printf("system time : %s\t\t\t\t %d byte sended\n",ptr,ret);

        Sleep((DWORD)100);     
    }

    closesocket(sListen);
    WSACleanup();    
    
    puts("press Enter to exit!");
    getchar();
    return 0;

}

客户端：

#include <stdio.h>
#include <winsock2.h>
#pragma  comment(lib,"ws2_32.lib ")

#define        SERVER_PORT        6666
#define        BUFFERLEN          128


int main()
{
    WORD    wVersionRequested;
    WSADATA    wsadata;
    int ret,i=0;
    SOCKET    sClient;

    struct sockaddr_in  saServer;
    char tmpbuf[BUFFERLEN];
    char    *ptr = tmpbuf;
    char    strIP[20];
    ULONG    wIP;
    char    flag[4]={'\\','|','/','-'};


    //winsock初始化
    wVersionRequested = MAKEWORD(2,2);
    ret = WSAStartup(wVersionRequested,&wsadata);
    if(ret != 0)
    {
        printf("WSAStartup() failed \n");
        return 1;
    }

    //确认Winsock DLL支持2.2版本
    if(LOBYTE(wsadata.wVersion) != 2 || HIBYTE(wsadata.wVersion) != 2)
    {
        WSACleanup();
        printf("Invalid winsock version \n");
        return 2;
    }

    //创建Socket 使用TCP协议
    sClient = socket(AF_INET,SOCK_STREAM,IPPROTO_TCP);
    if(sClient == INVALID_SOCKET)
    {
        WSACleanup();
        printf("socket() failed \n");
        return 3;
    }
    
    printf("Please input server's ip address :  ");
    scanf("%s",strIP);
    //构建服务器地址信息
    saServer.sin_family = AF_INET;
    saServer.sin_port = htons(SERVER_PORT);
    wIP = inet_addr(strIP);
    
    if(wIP == -1)
    {
        printf("wrong ip address");
        return -1;
    }
    saServer.sin_addr.S_un.S_addr = wIP;


    //连接服务器

    printf("connect to server ,please waitting...........\n");

    ret = connect(sClient,(struct sockaddr *)&saServer, sizeof(saServer));

    if(ret == SOCKET_ERROR)
    {
        printf("Can't connect server ,maybe server doesn't  startup   \n");
        printf("waitting   to  try  again ...........\\");
        Sleep((DWORD)500); 
    }
        
    while(ret == SOCKET_ERROR)
    {
        ret = connect(sClient,(struct sockaddr *)&saServer, sizeof(saServer));
        if(ret == SOCKET_ERROR)
        {
            i++;    
            i=i%4;
            printf("\b%c",flag[i]);
            Sleep((DWORD)500); 
        
        }
    }

    
    //接受数据
    while(1)
    {    
        ret = recv(sClient,ptr,BUFFERLEN,0);
        if(ret == SOCKET_ERROR)
        {
            printf("recv() failed \n");
            break;
        }

        if(ret == 0)
        {
            printf("Server has closed the connection \n");
            break;
        }
        

        printf("server time : %s\t\t\t\t %d byte received\n",ptr,ret);
        
    }    
        


    closesocket(sClient);
    WSACleanup();    
    
    puts("press Enter to exit!");
    getchar();
    return 0;
}

/* vi: set sw=4 ts=4: */
/* -------------------------------------------------------------------------
 * tftp.c
 *
 * A simple tftp client for busybox.
 * Tries to follow RFC1350.
 * Only "octet" mode supported.
 * Optional blocksize negotiation (RFC2347 + RFC2348)
 *
 * Copyright (C) 2001 Magnus Damm <[email]damm@opensource.se[/email]>
 *
 * Parts of the code based on:
 *
 * atftp:  Copyright (C) 2000 Jean-Pierre Lefebvre <[email]helix@step.polymtl.ca[/email]>
 *                        and Remi Lefebvre <[email]remi@[/email]>
 *
 * utftp:  Copyright (C) 1999 Uwe Ohse <[email]uwe@ohse.de[/email]>
 *
 * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
 * ------------------------------------------------------------------------- */

#include "libbb.h"


#if ENABLE_FEATURE_TFTP_GET || ENABLE_FEATURE_TFTP_PUT

#define TFTP_BLOCKSIZE_DEFAULT 512    /* according to RFC 1350, don't change */
#define TFTP_TIMEOUT 5    /* seconds */
#define TFTP_NUM_RETRIES 5 /* number of retries */

/* opcodes we support */
#define TFTP_RRQ   1
#define TFTP_WRQ   2
#define TFTP_DATA  3
#define TFTP_ACK   4
#define TFTP_ERROR 5
#define TFTP_OACK  6

#if ENABLE_FEATURE_TFTP_GET && !ENABLE_FEATURE_TFTP_PUT
#define USE_GETPUT(...)
#define CMD_GET(cmd) 1
#define CMD_PUT(cmd) 0
#elif !ENABLE_FEATURE_TFTP_GET && ENABLE_FEATURE_TFTP_PUT
#define USE_GETPUT(...)
#define CMD_GET(cmd) 0
#define CMD_PUT(cmd) 1
#else
#define USE_GETPUT(...) __VA_ARGS__
/* masks coming from getpot32 */
#define CMD_GET(cmd) ((cmd) & 1)
#define CMD_PUT(cmd) ((cmd) & 2)
#endif
/* NB: in the code below
 * CMD_GET(cmd) and CMD_PUT(cmd) are mutually exclusive
 */


#if ENABLE_FEATURE_TFTP_BLOCKSIZE

static int tftp_blocksize_check(int blocksize, int bufsize)
{
    /* Check if the blocksize is valid:
     * RFC2348 says between 8 and 65464,
     * but our implementation makes it impossible
     * to use blocksizes smaller than 22 octets.
     */

    if ((bufsize && (blocksize > bufsize))
     || (blocksize < 8) || (blocksize > 65564)
    ) {
        bb_error_msg("bad blocksize");
        return 0;
    }

    return blocksize;
}

static char *tftp_option_get(char *buf, int len, const char *option)
{
    int opt_val = 0;
    int opt_found = 0;
    int k;

    while (len > 0) {
        /* Make sure the options are terminated correctly */
        for (k = 0; k < len; k++) {
            if (buf[k] == '\0') {
                goto nul_found;
            }
        }
        return NULL;
 nul_found:
        if (opt_val == 0) {
            if (strcasecmp(buf, option) == 0) {
                opt_found = 1;
            }
        } else if (opt_found) {
            return buf;
        }

        k++;
        buf += k;
        len -= k;
        opt_val ^= 1;
    }

    return NULL;
}

#endif

static int tftp( USE_GETPUT(const int cmd,)
        len_and_sockaddr *peer_lsa,
        const char *remotefile, const int localfd,
        unsigned port, int tftp_bufsize)
{
    struct timeval tv;
    fd_set rfds;
    int socketfd;
    int len;
    int send_len;
    USE_FEATURE_TFTP_BLOCKSIZE(smallint want_option_ack = 0;)
    smallint finished = 0;
    uint16_t opcode;
    uint16_t block_nr = 1;
    uint16_t recv_blk;
    int timeout = TFTP_NUM_RETRIES;
    char *cp;

    unsigned org_port;
    len_and_sockaddr *const from = alloca(offsetof(len_and_sockaddr, sa) + peer_lsa->len);

    /* Can't use RESERVE_CONFIG_BUFFER here since the allocation
     * size varies meaning BUFFERS_GO_ON_STACK would fail */
    /* We must keep the transmit and receive buffers seperate */
    /* In case we rcv a garbage pkt and we need to rexmit the last pkt */
    char *xbuf = xmalloc(tftp_bufsize += 4);
    char *rbuf = xmalloc(tftp_bufsize);

    port = org_port = htons(port);

    socketfd = xsocket(peer_lsa->sa.sa_family, SOCK_DGRAM, 0);

    /* build opcode */
    opcode = TFTP_WRQ;
    if (CMD_GET(cmd)) {
        opcode = TFTP_RRQ;
    }
    cp = xbuf + 2;
    /* add filename and mode */
    /* fill in packet if the filename fits into xbuf */
    len = strlen(remotefile) + 1;
    if (2 + len + sizeof("octet") >= tftp_bufsize) {
        bb_error_msg("remote filename is too long");
        goto ret;
    }
    strcpy(cp, remotefile);
    cp += len;
    /* add "mode" part of the package */
    strcpy(cp, "octet");
    cp += sizeof("octet");

#if ENABLE_FEATURE_TFTP_BLOCKSIZE
    len = tftp_bufsize - 4;    /* data block size */
    if (len != TFTP_BLOCKSIZE_DEFAULT) {
        /* rfc2348 says that 65464 is a max allowed value */
        if ((&xbuf[tftp_bufsize - 1] - cp) < sizeof("blksize NNNNN")) {
            bb_error_msg("remote filename is too long");
            goto ret;
        }
        /* add "blksize", <nul>, blocksize */
        strcpy(cp, "blksize");
        cp += sizeof("blksize");
        cp += snprintf(cp, 6, "%d", len) + 1;
        want_option_ack = 1;
    }
#endif
    /* First packet is built, so skip packet generation */
    goto send_pkt;

    /* Using mostly goto's - continue/break will be less clear
     * in where we actually jump to */

    while (1) {
        /* Build ACK or DATA */
        cp = xbuf + 2;
        *((uint16_t*)cp) = htons(block_nr);
        cp += 2;
        block_nr++;
        opcode = TFTP_ACK;
        if (CMD_PUT(cmd)) {
            opcode = TFTP_DATA;
            len = full_read(localfd, cp, tftp_bufsize - 4);
            if (len < 0) {
                bb_perror_msg(bb_msg_read_error);
                goto ret;
            }
            if (len != (tftp_bufsize - 4)) {
                finished = 1;
            }
            cp += len;
        }
 send_pkt:
        /* Send packet */
        *((uint16_t*)xbuf) = htons(opcode); /* fill in opcode part */
        send_len = cp - xbuf;
        /* NB: send_len value is preserved in code below
         * for potential resend */
 send_again:
#if ENABLE_DEBUG_TFTP
        fprintf(stderr, "sending %u bytes\n", send_len);
        for (cp = xbuf; cp < &xbuf[send_len]; cp++)
            fprintf(stderr, "%02x ", (unsigned char) *cp);
        fprintf(stderr, "\n");
#endif
        xsendto(socketfd, xbuf, send_len, &peer_lsa->sa, peer_lsa->len);
        /* Was it final ACK? then exit */
        if (finished && (opcode == TFTP_ACK))
            goto ret;

        timeout = TFTP_NUM_RETRIES;    /* re-initialize */
 recv_again:
        /* Receive packet */
        tv.tv_sec = TFTP_TIMEOUT;
        tv.tv_usec = 0;
        FD_ZERO(&rfds);
        FD_SET(socketfd, &rfds);
        switch (select(socketfd + 1, &rfds, NULL, NULL, &tv)) {
            unsigned from_port;
        case 1:
            from->len = peer_lsa->len;
            memset(&from->sa, 0, peer_lsa->len);
            len = recvfrom(socketfd, rbuf, tftp_bufsize, 0,
                        &from->sa, &from->len);
            if (len < 0) {
                bb_perror_msg("recvfrom");
                goto ret;
            }
            from_port = get_nport(&from->sa);
            if (port == org_port) {
                /* Our first query went to port 69
                 * but reply will come from different one.
                 * Remember and use this new port */
                port = from_port;
                set_nport(peer_lsa, from_port);
            }
            if (port != from_port)
                goto recv_again;
            goto process_pkt;
        case 0:
            timeout--;
            if (timeout == 0) {
                bb_error_msg("last timeout");
                goto ret;
            }
            bb_error_msg("last timeout" + 5);
            goto send_again; /* resend last sent pkt */
        default:
            bb_perror_msg("select");
            goto ret;
        }
 process_pkt:
        /* Process recv'ed packet */
        opcode = ntohs( ((uint16_t*)rbuf)[0] );
        recv_blk = ntohs( ((uint16_t*)rbuf)[1] );

#if ENABLE_DEBUG_TFTP
        fprintf(stderr, "received %d bytes: %04x %04x\n", len, opcode, recv_blk);
#endif

        if (opcode == TFTP_ERROR) {
            static const char *const errcode_str[] = {
                "",
                "file not found",
                "access violation",
                "disk full",
                "illegal TFTP operation",
                "unknown transfer id",
                "file already exists",
                "no such user",
                "bad option"
            };

            const char *msg = "";

            if (rbuf[4] != '\0') {
                msg = &rbuf[4];
                rbuf[tftp_bufsize - 1] = '\0';
            } else if (recv_blk < ARRAY_SIZE(errcode_str)) {
                msg = errcode_str[recv_blk];
            }
            bb_error_msg("server error: (%u) %s", recv_blk, msg);
            goto ret;
        }

#if ENABLE_FEATURE_TFTP_BLOCKSIZE
        if (want_option_ack) {
            want_option_ack = 0;

            if (opcode == TFTP_OACK) {
                /* server seems to support options */
                char *res;

                res = tftp_option_get(&rbuf[2], len - 2, "blksize");
                if (res) {
                    int blksize = xatoi_u(res);
                    if (!tftp_blocksize_check(blksize, tftp_bufsize - 4)) {
                        /* send ERROR 8 to server... */
                        /* htons can be impossible to use in const initializer: */
                        /*static const uint16_t error_8[2] = { htons(TFTP_ERROR), htons(8) };*/
                        /* thus we open-code big-endian layout */
                        static const uint8_t error_8[4] = { 0,TFTP_ERROR, 0,8 };
                        xsendto(socketfd, error_8, 4, &peer_lsa->sa, peer_lsa->len);
                        bb_error_msg("server proposes bad blksize %d, exiting", blksize);
                        goto ret;
                    }
#if ENABLE_DEBUG_TFTP
                    fprintf(stderr, "using blksize %u\n",
                            blksize);
#endif
                    tftp_bufsize = blksize + 4;
                    /* Send ACK for OACK ("block" no: 0) */
                    block_nr = 0;
                    continue;
                }
                /* rfc2347:
                 * "An option not acknowledged by the server
                 *  must be ignored by the client and server
                 *  as if it were never requested." */
            }

            bb_error_msg("blksize is not supported by server"
                        " - reverting to 512");
            tftp_bufsize = TFTP_BLOCKSIZE_DEFAULT + 4;
        }
#endif
        /* block_nr is already advanced to next block# we expect
         * to get / block# we are about to send next time */

        if (CMD_GET(cmd) && (opcode == TFTP_DATA)) {
            if (recv_blk == block_nr) {
                len = full_write(localfd, &rbuf[4], len - 4);
                if (len < 0) {
                    bb_perror_msg(bb_msg_write_error);
                    goto ret;
                }
                if (len != (tftp_bufsize - 4)) {
                    finished = 1;
                }
                continue; /* send ACK */
            }
            if (recv_blk == (block_nr - 1)) {
                /* Server lost our TFTP_ACK.  Resend it */
                block_nr = recv_blk;
                continue;
            }
        }

        if (CMD_PUT(cmd) && (opcode == TFTP_ACK)) {
            /* did server ACK our last DATA pkt? */
            if (recv_blk == (uint16_t) (block_nr - 1)) {
                if (finished)
                    goto ret;
                continue; /* send next block */
            }
        }
        /* Awww... recv'd packet is not recognized! */
        goto recv_again;
        /* why recv_again? - rfc1123 says:
         * "The sender (i.e., the side originating the DATA packets)
         *  must never resend the current DATA packet on receipt
         *  of a duplicate ACK".
         * DATA pkts are resent ONLY on timeout.
         * Thus "goto send_again" will ba a bad mistake above.
         * See:
         * [url]http://en.'s_Apprentice_Syndrome[/url]
         */
    }
 ret:
    if (ENABLE_FEATURE_CLEAN_UP) {
        close(socketfd);
        free(xbuf);
        free(rbuf);
    }
    return finished == 0; /* returns 1 on failure */
}

int tftp_main(int argc, char **argv);
int tftp_main(int argc, char **argv)
{
    len_and_sockaddr *peer_lsa;
    const char *localfile = NULL;
    const char *remotefile = NULL;
#if ENABLE_FEATURE_TFTP_BLOCKSIZE
    const char *sblocksize = NULL;
#endif
    int port;
    USE_GETPUT(int cmd;)
    int fd = -1;
    int flags = 0;
    int result;
    int blocksize = TFTP_BLOCKSIZE_DEFAULT;

    /* -p or -g is mandatory, and they are mutually exclusive */
    opt_complementary = "" USE_FEATURE_TFTP_GET("g:") USE_FEATURE_TFTP_PUT("p:")
            USE_GETPUT("?g--p:p--g");

    USE_GETPUT(cmd =) getopt32(argv,
            USE_FEATURE_TFTP_GET("g") USE_FEATURE_TFTP_PUT("p")
                "l:r:" USE_FEATURE_TFTP_BLOCKSIZE("b:"),
            &localfile, &remotefile
            USE_FEATURE_TFTP_BLOCKSIZE(, &sblocksize));
    argv += optind;

    flags = O_RDONLY;
    if (CMD_GET(cmd))
        flags = O_WRONLY | O_CREAT | O_TRUNC;

#if ENABLE_FEATURE_TFTP_BLOCKSIZE
    if (sblocksize) {
        blocksize = xatoi_u(sblocksize);
        if (!tftp_blocksize_check(blocksize, 0)) {
            return EXIT_FAILURE;
        }
    }
#endif

    if (!localfile)
        localfile = remotefile;
    if (!remotefile)
        remotefile = localfile;
    /* Error if filename or host is not known */
    if (!remotefile || !argv[0])
        bb_show_usage();

    fd = CMD_GET(cmd) ? STDOUT_FILENO : STDIN_FILENO;
    if (!LONE_DASH(localfile)) {
        fd = xopen(localfile, flags);
    }

    port = bb_lookup_port(argv[1], "udp", 69);
    peer_lsa = xhost2sockaddr(argv[0], port);

#if ENABLE_DEBUG_TFTP
    fprintf(stderr, "using server '%s', remotefile '%s', localfile '%s'\n",
            xmalloc_sockaddr2dotted(&peer_lsa->sa),
            remotefile, localfile);
#endif

    result = tftp( USE_GETPUT(cmd,) peer_lsa, remotefile, fd, port, blocksize);

    if (ENABLE_FEATURE_CLEAN_UP)
        close(fd);
    if (result != EXIT_SUCCESS && !LONE_DASH(localfile) && CMD_GET(cmd)) {
        unlink(localfile);
    }
    return result;
}

#endif /* ENABLE_FEATURE_TFTP_GET || ENABLE_FEATURE_TFTP_PUT */

刚学网络编程还是使用Socket套接字好些，用高级的库难以理解底层。

要做FTP的话要准备好一些东西
1.RFC95协议 这个是标准的FTP协议
2.知道socket的最简单的通信(完成从1台机器给另1台机器发1个hello!开始)
3.最好下一个嗅探器 我建议你使用 wireshark ,嗅探器可以很好的监控你的端口究竟做了什么,比如
      谁给谁发了什么请求,谁给谁发了什么回应,这些请求和回应的格式 反正这些都是固定的套路
4.了解tcp/ip协议,你说的FTP 就是为了完成一次会话.
5.自己下1个人家写好的ftp服务器端的软件(不要程序,就是可执行的),把你的嗅探器打开,从登陆开始→使用get或put→quit 观察嗅探器 里这次会话是怎么完成的.

你做的这个实验 我也做过,是用C写1个FTP服务器(linux),完了在WINDOWS下的用CMD里的FTP客户端登陆 完成get put ls quit命令.
完了,老师又叫我们写了个http服务器(跟FTP原理差不多).