您需要循环发送方和接收。无论是发送（）也不的recv（）保证发送/当你请求的读取的字节数。

You need to loop both the sending and receiving. Neither send() nor recv() are guaranteed to send/read as many bytes as you requested.

您还应该让接收器知道多少字节期望以及何时停止读取文件数据之前发送的文件大小。

You also should send the file size before the file data so the receiver knows how many bytes to expect and when to stop reading.

尝试这样的东西更多：

服务器

bool senddata(SOCKET sock, void *buf, int buflen)
{
    unsigned char *pbuf = (unsigned char *) buf;

    while (buflen > 0)
    {
        int num = send(sock, pbuf, buflen, 0);
        if (num == SOCKET_ERROR)
        {
            if (WSAGetLastError() == WSAEWOULDBLOCK)
            {
                // optional: use select() to check for timeout to fail the send
                continue;
            }
            return false;
        }

        pbuf += num;
        buflen -= num;
    }

    return true;
}

bool sendlong(SOCKET sock, long value)
{
    value = htonl(value);
    return senddata(sock, &value, sizeof(value));
}

bool sendfile(SOCKET sock, FILE *f)
{
    fseek(f, 0, SEEK_END);
    long filesize = ftell(f);
    rewind(f);
    if (filesize == EOF)
        return false;
    if (!sendlong(sock, filesize))
        return false;
    if (filesize > 0)
    {
        char buffer[1024];
        do
        {
            size_t num = min(filesize, sizeof(buffer));
            num = fread(buffer, 1, num, f);
            if (num < 1)
                return false;
            if (!senddata(sock, buffer, num, 0))
                return false;
            filesize -= num;
        }
        while (filesize > 0);
    }
    return true;
}

FILE *filehandle = fopen("imagefile.jpg", "rb");
if (filehandle != NULL)
{
    sendfile(clientsocket, filehandle);
    fclose(filehandle);
}

客户端

bool readdata(SOCKET sock, void *buf, int buflen)
{
    unsigned char *pbuf = (unsigned char *) buf;

    while (buflen > 0)
    {
        int num = recv(sock, pbuf, buflen, 0);
        if (num == SOCKET_ERROR)
        {
            if (WSAGetLastError() == WSAEWOULDBLOCK)
            {
                // optional: use select() to check for timeout to fail the read
                continue;
            }
            return false;
        }
        else if (num == 0)
            return false;

        pbuf += num;
        buflen -= num;
    }

    return true;
}

bool readlong(SOCKET sock, long *value)
{
    if (!readdata(sock, value, sizeof(value)))
        return false;
    *value = ntohl(*value);
    return true;
}

bool readfile(SOCKET sock, FILE *f)
{
    long filesize;
    if (!readlong(sock, &filesize))
        return false;
    if (filesize > 0)
    {
        char buffer[1024];
        do
        {
            int num = min(filesize, sizeof(buffer));
            if (!readdata(sock, buffer, num))
                return false;
            int offset = 0;
            do
            {
                size_t written = fwrite(&buffer[offset], 1, num-offset, f);
                if (written < 1)
                    return false;
                offset += written;
            }
            while (offset < num);
            filesize -= num;
        }
        while (filesize > 0);
    }
    return true;
}

FILE *filehandle = fopen("imagefile.jpg", "wb");
if (filehandle != NULL)
{
    bool ok = readfile(clientsocket, filehandle);
    fclose(filehandle);

    if (ok)
    {
        // use file as needed...
    }
    else
        remove("imagefile.jpg");
}