The best replacement for stringstream is ostringstream.

The best alternatives to stringstream are rated as following:
★★★★★  ostringstream
★★★★  string append
★★★  sscanf
★★★  atoi
★★  stringbuf
★★  lexical_cast
★  strtol
★  sprintf
★  strstream
★  sstream

Your alternative for stringstream is not listed? Suggest!
Speaking about stringstream, one probably shouldn't forget about getline.

Other search terms related to stringstream and their ratings are:
★★★★★ getline
You have in mind a companion for stringstream and it is not yet here? Propose!



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stringstream
ostringstream
string append