将字符串连接到自己的协议中

我正在用socket.h编写网络程序来学习。我已经编写了服务器和客户端简单的程序，可以使用用户指定的缓冲区大小在它们之间传输文件。

    void transfer(string name)
{
    char *data_to_send;
    ifstream myFile;
    myFile.open(name.c_str(),ios::binary);
    if(myFile.is_open))
    {
        while(myFile.eof))
        {
            data_to_send = new char [buffer_size];
            myFile.read(data_to_send, buffer_size);
            send(data_to_send,buffer_size);
            delete [] data_to_send;
        }
        myFile.close();
        send("03endtransmission",buffer_size);
    }
    else
    {
        send("03error",buffer_size);
    }
}

void download(string name)
{
    char *received_data;
    fstream myFile;
    myFile.open(name.c_str(),ios::out|ios::binary);
    if(myFile.is_open()) 
    {
        while(1)
        {
            received_data = new char[rozmiar_bufora];
            if((receivedB = recv(sockfd, received_data, buffer_size,0)) == -1) {
                perror("recv");
                close(sockfd);
                exit(1);
            }
            if(strcmp(received_data,"03endoftransmission") == 0)
            {
                cout<<"End of transmission"<<endl;
                break;
            }
            else if (strcmp(received_data,"03error") == 0)
            {
                cout<<"Error"<<endl;
                break;
            }
            myFile.write(received_data,buffer_size);
        }
        myFile.close();
    }

问题发生了，当我想实现我自己的协议-两个字符(控制)，32个字符哈希，其余的包是数据。我尝试了几次将其分割，最后得到以下代码:

#define PAYLOAD 34
void transfer(string name)
{
    char hash[] = "12345678901234567890123456789012"; //32 chars
    char *data_to_send;
    ifstream myFile;
    myFile.open(name.c_str(),ios::binary);
    if(myFile.is_open))
    {
        while(myFile.eof))
        {
            data_to_send = new char [buffer_size-PAYLOAD];
            myFile.read(data_to_send, buffer_size-PAYLOAD);
            concatenation = new char[buffer_size];
            strcpy(concatenation,"02");
            strcat(concatenation,hash);
            strcat(concatenation,data_to_send);
            send(concatenation,buffer_size);
            delete [] data_to_send;
            delete [] concatenation;
        }
        myFile.close();
        send("03endtransmission",buffer_size);
    }
    else
    {
        send("03error",buffer_size);
    }
}

void download(string name)
{
    char *received_data;
    fstream myFile;
    myFile.open(name.c_str(),ios::out|ios::binary);
    if(myFile.is_open()) 
    {
        while(1)
        {
            received_data = new char[buffer_size];
            if((receivedB = recv(sockfd, received_data, buffer_size,0)) == -1) {
                perror("recv");
                close(sockfd);
                exit(1);
            }
            if(strcmp(received_data,"03endoftransmission") == 0)
            {
                cout<<"End of transmission"<<endl;
                break;
            }
            else if (strcmp(received_data,"03error") == 0)
            {
                cout<<"Error"<<endl;
                break;
            }
            control = new char[3];
            strcpy(control,"");
            strncpy(control, received_data,2);
            control[2]='';
            hash = new char[33];
            strcpy(hash,"");
            strncpy(hash,received_data+2,32);
            hash[32]='';
            data = new char[buffer_size-PAYLOAD+1];
            strcpy(data,"");
            strncpy(data,received_data+34,buffer_size-PAYLOAD);
            myFile.write(data,buffer_size-PAYLOAD);
        }
        myFile.close();
    }

但是这个输入文件一些^@而不是实际数据。在服务器和客户机上向控制台显示"数据"看起来是一样的。如果你知道怎么分的话，我会很感激的。