C OpenSSL upgrading connection to TLS

Code
#include <openssl/bio.h>

#include <openssl/ssl.h>

#include <openssl/err.h>

#include <vector>



int main(){

    

    std::string HelloString = "ehlo 127.0.0.1\r\n";

    std::vector<char> buffer(5000);



    //Connect to gmail SMTP server

    BIO * bio = BIO_new_connect("smtp.gmail.com:587"); 

    BIO_do_connect(bio);

    

    //Read server hello

    BIO_read(bio, buffer.data(), buffer.size());



    //write client hello

    BIO_write(bio, HelloString.c_str(), HelloString.length());



    //read server ack and commands

    BIO_read(bio, buffer.data(), buffer.size());



    //Tell the server I want to upgrade the connection

    BIO_write(bio, "STARTTLS\r\n", 10);



    //Upgrade the connection some how

    //Edited Version

    SSL_CTX * ctx = SSL_CTX_new(SSLv23_client_method());

    BIO * ssl_bio = BIO_new_ssl(ctx, 1);



    BIO * ssl_chain = BIO_push(ssl_bio, bio);

    BIO_do_handshake(ssl_chain);



    //Completed - Start sending data as TLS





    return 0;

}