Boost library write_json put extra new line at the end

Question

I am learning from http://www.cochoy.fr/boost-property-tree/. Instead of write_json to stdout, I tried to save it in a string.

std::stringstream  ss;
boost::property_tree::json_parser::write_json(ss, oroot, false);
std::cout <<" begin json string" << std::endl;
std::cout << ss.str() << std::endl;
std::cout << "after json string" << std::endl;

output:

 begin json string
{"height":"320","some":{"complex":{"path":"bonjour"}},"animals":{"rabbit":"white","dog":"brown","cat":"grey"},"fish":"blue","fish":"yellow","fruits":["apple","raspberry","orange"],"matrix":[["1","2","3"],["4","5","6"],["7","8","9"]]}

after json string

According to the output above, there is a new empty line at the end. How to get rid of the new line? Because with the new line it is not a valid JSON string.

Answer 1

The newline is not explicitly mentioned in the JSON RFC-7159 but it is defined as part of the POSIX standard for a line.

Incase you're interested in where the newline comes from you can take a look at the write_json_internal source code, we can see that there is an stream << std::endl; near the end of the method. Note that ...::write_json references write_json_internal.

 // Write ptree to json stream
template<class Ptree>
void write_json_internal(std::basic_ostream<typename Ptree::key_type::value_type> &stream, 
                         const Ptree &pt,
                         const std::string &filename,
                         bool pretty)
{
    if (!verify_json(pt, 0))
        BOOST_PROPERTY_TREE_THROW(json_parser_error("ptree contains data that cannot be represented in JSON format", filename, 0));
    write_json_helper(stream, pt, 0, pretty);
    stream << std::endl;
    if (!stream.good())
        BOOST_PROPERTY_TREE_THROW(json_parser_error("write error", filename, 0));
}