How to rename a key during looping? #893

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1. nlohmann commented on Dec 27, 2017

   

   nlohmann

   on Dec 27, 2017

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   This is not possible. JSON objects are stored internally as std::map. Their keys are const while iterating.
2. gestern commented on Dec 27, 2017

   

   gestern

   on Dec 27, 2017

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   Thanks, so just to understand, in general, is there any chance to easy rename a key, means without using a pair remove/insert? Like rapidjson:

   it->name.SetString ("new key", d.GetAllocator());
3. gestern

   closed this as completedon Dec 27, 2017
4. gestern

   reopened this on Dec 27, 2017
5. gestern

   closed this as completedon Dec 28, 2017
6. nlohmann commented on Dec 28, 2017

   

   nlohmann

   on Dec 28, 2017

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   You can use this function:

   #include <iostream>
   #include "json.hpp"
   
   using json = nlohmann::json;
   
   void change_key(json &object, const std::string& old_key, const std::string& new_key)
   {
       // get iterator to old key; TODO: error handling if key is not present
       json::iterator it = object.find(old_key);
       // create null value for new key and swap value from old key
       std::swap(object[new_key], it.value());
       // delete value at old key (cheap, because the value is null after swap)
       object.erase(it);
   }
   
   int main()
   {
       json j;
       j["foo"] = "value";
       
       std::cout << j << std::endl;
   
       change_key(j, "foo", "bar");
       
       std::cout << j << std::endl;
   }

   Output:

   {"foo":"value"}
   {"bar":"value"}

   I just adjusted code from https://stackoverflow.com/a/5743682/266378.
7. nlohmann

   added

   solution: proposed fixa fix for the issue has been proposed and waits for confirmationa fix for the issue has been proposed and waits for confirmation

   on Dec 28, 2017