If you visit the [operator >> (istream &, basic_json &) reference](https://nlohmann.github.io/json/classnlohmann_1_1basic__json_aaf363408931d76472ded14017e59c9e8.html#aaf363408931d76472ded14017e59c9e8) you will notice that a sample is for operator <<(basic_json&, ostream&)
If you visit the operator >> (istream &, basic_json &) reference you will notice that a sample is for operator <<(basic_json&, ostream&)