How to change json object name without changing its values in C++? - c++

Question

I'm using json for modern c++.
And I have a json file which contains some data like:
{
"London": {
"Adress": "londonas iela 123",
"Name": "London",
"Shortname": "LL"
},
"Riga": {
"Adrese": "lidostas iela 1",
"Name": "Riga",
"Shortname": "RIX"
}
And I found out a way to modify the values of "Adrese", "Name", "Shortname".
As you can see I have "name" and key element name set to the same thing.
But I need to change both the key element and value "name".
So at the end when somehow in the code I modify it, it would look like:
{
"Something_New": {
"Adress": "londonas iela 123",
"Name": "Something_New",
"Shortname": "LL"
},
"Riga": {
"Adrese": "lidostas iela 1",
"Name": "Riga",
"Shortname": "RIX"
}
I've tried:
/other_code/
json j
/functions_for_opening_json file/
j["London"]["Name"] = "Something_New"; //this changes the value "name"
j["London"] = "Something_New"; //But this replaces "London" with
"Something_new" and deletes all of its inside values.
Then I tried something like:
for(auto& el : j.items()){
if(el.key() == "London"){
el.key() = "Something_New";}
}
But that didn't work either.
I would like something like j["London"] = "Something_new", and for it to keep all the values that originally was for "London".

Answer 1

The value associated with key "London" is the entire subtree json object containing the other 3 keys with their values. This line j["London"] = "Something_New"; does not change the key, "London" but its value. So you end up with the pair "London" : "Something new", overwriting the json subtree object. The keys are stored internally as std::map . Therefore you can't simply rename a key like that. Try:
void change_key(json &j, const std::string& oldKey, const std::string& newKey)
{
auto itr = j.find(oldKey); // try catch this, handle case when key is not found
std::swap(j[newKey], itr.value());
object.erase(itr);
}
And then
change_key(j, "London", "Something_New");