Error when etablishing a TLS connection to smtp.gmail.com

Question

I'm trying to connect to smtp.gmail.com with C++ code, and I think I need openSSL. I installed it and successfully connect to server with command line,

openssl s_client -starttls smtp -connect smtp.gmail.com:587

but I got trouble when establish connection in code, see the last few sentences of the code.

Could anyone please help?

    void main ()
    {
        int err;
        int sd;
        struct sockaddr_in sa;
        SSL_CTX* ctx;
        SSL* ssl;
        X509* server_cert;
        char* str;
        const SSL_METHOD *meth;

        WSADATA wsaData;

        if(WSAStartup(MAKEWORD(2,2),&wsaData) != 0){
        printf("WSAStartup()fail:%d\n",GetLastError());
        return -1;
        } 

        SSL_library_init();

        SSL_load_error_strings(); 

        meth = TLSv1_2_client_method();
        ctx = SSL_CTX_new (meth); 
        CHK_NULL(ctx);


        // begin win socket .............................. 
        printf("Begin tcp socket...\n");

        sd = socket (AF_INET, SOCK_STREAM, 0); CHK_ERR(sd, "socket");

        memset (&sa, 0, sizeof(sa));
        sa.sin_family = AF_INET;
        sa.sin_addr.s_addr = inet_addr (SERVER_ADDR); /* Server IP */
        sa.sin_port = htons (PORT); /* Server Port number */

        err = connect(sd, (struct sockaddr*) &sa,  sizeof(sa)); 
        if( sd == SOCKET_ERROR  ) {
        std::cout<<"connect error."<<std::endl;
        return -1;
        }


        /* SSl negotiation .................. */
        printf("Begin SSL negotiation \n");

        ssl = SSL_new (ctx); 
        CHK_NULL(ssl);

        SSL_set_fd (ssl, sd);

    //ssl connect error here????        
    //What's wrong

        err = SSL_connect (ssl);
        if (err == -1)
        {
        ERR_print_errors_fp(stderr);
        }
    }