Read Ctxt from stream in using HElib

Assume you need to read Ctxt from a stream (file, socket, or whatever) in using HElib, the general pattern is like this:

Ctxt ctxt(*pubKey);
while (fs >> ctxt)
{
    std::cout << ++count << std::endl;
}

But this will trigger following error (If you use one version of HElib to encrypt Ctxt, while use another version of HElib to process Ctxt, this error may occur too.):

Searching for cc='[' (ascii 91), found c='▒' (ascii -1)

The root cause of this issue is about handling EOF. To solve this issue, there are 2 methods:

(1)

Ctxt ctxt(*pubKey);
while (!fs.eof())
{
    fs >> ctxt >> std::ws;
    if (fs.fail())
    {
        break;
    }
}

fs >> ctxt >> std::ws; will stop when the EOF is met. Since fs.fail() won’t return true when eofbit is set (please refer here), fs.eof() will becometrue to terminate while-loop.

(2) know how many Ctxt will be read in advance. For example:

Ctxt ctxt(*pubKey);
for (int i = 0; i < 10; i++)
{
    fs >> ctxt;
}