You can use the EncryptedArray::encrypt(Ctxt& ctxt, const FHEPubKey& pKey, const vector< long >& ptxt) method. Slot content is given by the third parameter ptxt.

Thanks for your reply. Would you mind giving an example to further explain how to realize this method? That will be grateful.

In the context of Test_General.cpp something like this (replace line 130 with):

vector<long> content(nslots, 0); //all slots to 0
content[42] = 1; //42-th slot to 1
ea.encrypt(c1, publicKey, p1);

Whoo, that's great. Thanks again for your explanation.

Welcome :)

I don't know how this affect p1. I've tested those codes. The result is that p1 wasn't changed. In my project, I want p1 in the class plaintextarray but long for the further computation.

Sorry, it was a typo. The last line must be:
ea.encrypt(c1, publicKey, content);

Well, the data type in the vector was still 'long'. However, I wanted it to be 'plaintextarray'. Is there any treatment I can do?