std::ifstream pointer position not reset-ed after being used by json::accept(file);

[kenzanin]

code:

    std::ifstream ifs(filename.data(), std::ifstream::in);
    if (!json::accept(ifs)) {
      log->critical("error file {} not valid config.", filename);
      std::exit(EXIT_FAILURE);
    }
    js = nlohmann::json::parse(ifs);
    log->debug("{}", js.dump());

expected:
js contains json object

actual:
terminate called after throwing an instance of 'nlohmann::json_abi_v3_11_2::detail::parse_error'
what(): [json.exception.parse_error.101] parse error at line 1, column 1: syntax error while parsing value - unexpected end of input; expected '[', '{', or a literal

working:

    std::ifstream ifs(filename.data(), std::ifstream::in);
    if (!json::accept(ifs)) {
      log->critical("error file {} not valid config.", filename);
      std::exit(EXIT_FAILURE);
    }
    ifs.seekg(0); // add this
    js = nlohmann::json::parse(ifs);
    log->debug("{}", js.dump());

question:
is this intentional?

thanks

[nlohmann]

Yes, this is intentional:

• You need to reset your stream if you want to read it again.
• The library does not mess with the stream position and leaves the stream past the last byte it read. This allows use cases like https://json.nlohmann.me/features/parsing/json_lines/

[kenzanin]

thanks