newbie question on base64/ RSA decoding

[Stephan Stapel]

Dear people on this list!
I've been 'playing' around with CryptoPP for quite some time now and 
have some problems decrypting a base64-encoded string I've encrypted before.
My code looks like this:

CryptoPP::RSAES_OAEP_SHA_Decryptor privkey(rng, 1024);
CryptoPP::RSAES_OAEP_SHA_Encryptor pubkey(privkey);
// .....
// encrypt a string
CryptoPP::SecByteBlock 
sbbCipherText(pubkey.CiphertextLength(szClearText.size()));

pubkey.Encrypt(rng,
               (byte const*)szClearText.data(),
               szClearText.size(),
               sbbCipherText.begin());
std::string resultEncoded;
CryptoPP::Base64Encoder be3(new CryptoPP::StringSink(resultEncoded));
be3.Put(sbbCipherText.begin(), sbbCipherText.size());
std::cout << "Encrypted string: " << resultEncoded << std::endl;
// decrypt the string
char szDecoded[1024];
CryptoPP::DecodingResult dresult = privkey.Decrypt(
                                     rng,
                                     (const byte*)sbbCipherText.data(),
                                     sbbCipherText.size(),
                                     (byte*)szDecoded);
szDecoded[dresult.messageLength] = '\0';
std::string szCleartextEncoded   = std::string(szDecoded);
std::cout << "Decrypted string: " << szCleartextEncoded << std::endl;
This works really fine. But what I would like to achieve is to use the 
base64 encoded string 'resultEncoded' as the input for decryption which 
I don't get going though trying hard.

Can someone please help me out on this?
Thanks in advance
and
kind regards,
Stephan