conversion to std::string failed

[somequery]

I have difficulties with dumping all data from a json object into a string.

I created a json object with multyple fields and assigned values to them. The data types are std::string, unsigned int, ushort, and pid_t. I can successfully read the data back with a statement:
jsonMsg[item_name].get<item_type>();

However, when I want to return the created json object as a std::string object, this fails:
std::string strJson = jsonMsg.get<std::string>();
also this:
std::string strJson = jsonMsg.dump();

I want to represent the nlohmann::json as bunch of bytes stored in std::string so I could pass it across software modules and at the end just convert these bytes back to nlohmann json object.

I was doing this with the boost property tree. Can I do it with nlohmann json?

Thank you for help.

[somequery]

I found extended ASCII characters in one field which causes the problem.