c – send()崩溃了我的程序

这是服务器中向客户端发送数据的函数：

int sendToClient(int fd,string msg) {

    cout << "sending to client " << fd << " " << msg <<endl;
    int len = msg.size()+1;
    cout << "10n";
    /* send msg size */
    if (send(fd,&len,sizeof(int),0)==-1) {
        cout << "error sendToClientn";
        return -1;
    }
    cout << "11n";
    /* send msg */
    int nbytes = send(fd,msg.c_str(),len,0); //CRASHES HERE
    cout << "15n";
    return nbytes;
}

当客户端退出时,它发送到服务器“BYE”,服务器正在使用上述功能回复它.我将客户端连接到服务器(在一台计算机上完成,2个终端),当客户端退出服务器崩溃时 – 它从不打印15.
任何想法为什么？任何想法如何测试为什么？

谢谢.

编辑：这是我关闭客户端的方式：

void closeClient(int notifyServer = 0) {

/** notify server before closing */
if (notifyServer) {
    int len = SERVER_PROTOCOL[bye].size()+1;
    char* buf = new char[len];
    strcpy(buf,SERVER_PROTOCOL[bye].c_str());   //c_str - NEED TO FREE????
    sendToServer(buf,len);
    delete[] buf;
}
close(_sockfd);
}

顺便说一下,如果我跳过这段代码,意味着离开关闭(_sockfd)而不通知服务器一切正常 – 服务器不会崩溃.

编辑2：这是strace.out的结束：

5211  recv(5,"BYE",4,0)            = 4
5211  write(1,"received from client 5 n",24) = 24
5211  write(1,"command: BYE msg: n",19) = 19
5211  write(1,"BYEBYEn",7)           = 7
5211  write(1,"response = ALALA!!!n",20) = 20
5211  write(1,"sending to client 5 ALALA!!!n",29) = 29
5211  write(1,"10n",3)               = 3
5211  send(5,"t",0)         = 4
5211  write(1,"11n","ALALA!!!",9,0)       = -1 EPIPE (Broken pipe)
5211  --- SIGPIPE (Broken pipe) @ 0 (0) ---
5211  +++ killed by SIGPIPE +++

破管可以杀死我的程序??为什么不通过send()返回-1？