If the text file delimits paragraphs the usual way (a new line character), then just use the global function std::getline(). Even if they were delimited with some other character, I believe this function would still be able to do the job.
If there are multiple paragraphs, and between paragraphs you have multiple newline delimiters, I believe getline() will produce an empty string. If this happens, just ignore it and move on to the next line.