runme.cpp

#include <ArduinoJson.h>
#include <iostream>

int main(int argc, char **argv) {
    DynamicJsonBuffer buffer(1024);

    JsonObject& shared = buffer.createObject();

    JsonObject& a = buffer.createObject();
    JsonObject& b = buffer.createObject();

    shared["these"] = "strings";
    shared["are"] = "shared";

    a["shared"] = shared;
    b["shared"] = shared;
    shared["and"] = "this";

    std::string out_a;
    a.printTo(out_a);
    std::cout << out_a << std::endl;

    std::string out_b;
    a.printTo(out_b);
    std::cout << out_b << std::endl;
}

runme2.cpp

#include <string>
#include <iostream>
#include <chrono>
#include <thread>

#include "ArduinoJson.h"

int main(int argc, char **argv) {
    DynamicJsonBuffer buffer(1024);

    JsonObject& root = buffer.createObject();
    JsonObject& shared = buffer.createObject();
    JsonObject& new_root = root.createNestedObject("new_root");
    new_root["shared"] = shared;

    shared["these"] = "strings";
    shared["are"] = "shared";

    std::string out;
    std::string buf;
    for (int count=0; count < 1000; ++count) {

        buf = std::to_string(count);
        new_root["count"] = buf.c_str();
        new_root["const"] = "const string";
        new_root["count_int"] = count;
        new_root.printTo(out);

        std::cout << "size:" << buffer.size() << " | data:" << out << std::endl;
        out = "";

        std::this_thread::sleep_for(std::chrono::milliseconds(200));
    }

}

runme2.txt

$ git diff
diff --git a/src/ArduinoJson/DynamicJsonBuffer.hpp b/src/ArduinoJson/DynamicJsonBuffer.hpp
index 7fe2b68..4a37aa2 100644
--- a/src/ArduinoJson/DynamicJsonBuffer.hpp
+++ b/src/ArduinoJson/DynamicJsonBuffer.hpp
@@ -7,6 +7,7 @@
 #include "JsonBufferBase.hpp"

 #include <stdlib.h>
+#include <stdio.h>

 #if defined(__clang__)
 #pragma clang diagnostic push
@@ -23,9 +24,12 @@ namespace Internals {
 class DefaultAllocator {
  public:
   void* allocate(size_t size) {
-    return malloc(size);
+    void *ptr = malloc(size);
+    printf("+ %p malloc(%zu)\n", ptr, size);
+    return ptr;
   }
   void deallocate(void* pointer) {
+    printf("- %p free()\n", pointer);
     free(pointer);
   }
 };
$ ./runme2
+ 0x7fffd3f00e70 malloc(1048)
size:272 | data:{"shared":{"these":"strings","are":"shared"},"count":"0","const":"const string","count_int":0}
size:272 | data:{"shared":{"these":"strings","are":"shared"},"count":"1","const":"const string","count_int":1}
size:272 | data:{"shared":{"these":"strings","are":"shared"},"count":"2","const":"const string","count_int":2}
size:272 | data:{"shared":{"these":"strings","are":"shared"},"count":"3","const":"const string","count_int":3}
size:272 | data:{"shared":{"these":"strings","are":"shared"},"count":"4","const":"const string","count_int":4}
size:272 | data:{"shared":{"these":"strings","are":"shared"},"count":"5","const":"const string","count_int":5}
size:272 | data:{"shared":{"these":"strings","are":"shared"},"count":"6","const":"const string","count_int":6}
size:272 | data:{"shared":{"these":"strings","are":"shared"},"count":"7","const":"const string","count_int":7}
size:272 | data:{"shared":{"these":"strings","are":"shared"},"count":"8","const":"const string","count_int":8}
size:272 | data:{"shared":{"these":"strings","are":"shared"},"count":"9","const":"const string","count_int":9}
size:272 | data:{"shared":{"these":"strings","are":"shared"},"count":"10","const":"const string","count_int":10}
size:272 | data:{"shared":{"these":"strings","are":"shared"},"count":"11","const":"const string","count_int":11}
size:272 | data:{"shared":{"these":"strings","are":"shared"},"count":"12","const":"const string","count_int":12}
size:272 | data:{"shared":{"these":"strings","are":"shared"},"count":"13","const":"const string","count_int":13}
size:272 | data:{"shared":{"these":"strings","are":"shared"},"count":"14","const":"const string","count_int":14}

runme3.diff

--- run.cpp     2019-10-24 15:51:21.364712300 +0300
+++ run2.cpp    2019-10-24 15:52:38.721239600 +0300
@@ -10,9 +10,6 @@

     JsonObject& root = buffer.createObject();
     JsonObject& shared = buffer.createObject();
-    JsonObject& new_root = root.createNestedObject("new_root");
-    new_root["shared"] = shared;
-

     shared["these"] = "strings";
     shared["are"] = "shared";
@@ -20,6 +17,9 @@
     std::string out;
     std::string buf;
     for (int count=0; count < 1000; ++count) {
+        JsonObject& new_root = root.createNestedObject("new_root");
+        new_root["shared"] = shared;
+
         buf = std::to_string(count);
         new_root["count"] = buf.c_str();
         new_root["const"] = "const string";
@@ -27,6 +27,7 @@
         new_root.printTo(out);

         std::cout << "size:" << buffer.size() << " | data:" << out << std::endl;
+        root.remove("new_root");
         out = "";

         std::this_thread::sleep_for(std::chrono::milliseconds(200));

runme3.txt

$ ./runme3
+ 0x7fffe7e76e70 malloc(1048)
size:272 | data:{"shared":{"these":"strings","are":"shared"},"count":"0","const":"const string","count_int":0}
size:416 | data:{"shared":{"these":"strings","are":"shared"},"count":"1","const":"const string","count_int":1}
size:560 | data:{"shared":{"these":"strings","are":"shared"},"count":"2","const":"const string","count_int":2}
size:704 | data:{"shared":{"these":"strings","are":"shared"},"count":"3","const":"const string","count_int":3}
size:848 | data:{"shared":{"these":"strings","are":"shared"},"count":"4","const":"const string","count_int":4}
size:992 | data:{"shared":{"these":"strings","are":"shared"},"count":"5","const":"const string","count_int":5}
+ 0x7fffe7e777b0 malloc(2072)
size:1136 | data:{"shared":{"these":"strings","are":"shared"},"count":"6","const":"const string","count_int":6}
size:1280 | data:{"shared":{"these":"strings","are":"shared"},"count":"7","const":"const string","count_int":7}
size:1424 | data:{"shared":{"these":"strings","are":"shared"},"count":"8","const":"const string","count_int":8}
size:1568 | data:{"shared":{"these":"strings","are":"shared"},"count":"9","const":"const string","count_int":9}
size:1712 | data:{"shared":{"these":"strings","are":"shared"},"count":"10","const":"const string","count_int":10}
size:1856 | data:{"shared":{"these":"strings","are":"shared"},"count":"11","const":"const string","count_int":11}
size:2000 | data:{"shared":{"these":"strings","are":"shared"},"count":"12","const":"const string","count_int":12}
size:2144 | data:{"shared":{"these":"strings","are":"shared"},"count":"13","const":"const string","count_int":13}
size:2288 | data:{"shared":{"these":"strings","are":"shared"},"count":"14","const":"const string","count_int":14}
size:2432 | data:{"shared":{"these":"strings","are":"shared"},"count":"15","const":"const string","count_int":15}
size:2576 | data:{"shared":{"these":"strings","are":"shared"},"count":"16","const":"const string","count_int":16}
size:2720 | data:{"shared":{"these":"strings","are":"shared"},"count":"17","const":"const string","count_int":17}
size:2864 | data:{"shared":{"these":"strings","are":"shared"},"count":"18","const":"const string","count_int":18}
size:3008 | data:{"shared":{"these":"strings","are":"shared"},"count":"19","const":"const string","count_int":19}
+ 0x7fffe7e77fd0 malloc(4120)
size:3152 | data:{"shared":{"these":"strings","are":"shared"},"count":"20","const":"const string","count_int":20}
size:3296 | data:{"shared":{"these":"strings","are":"shared"},"count":"21","const":"const string","count_int":21}
size:3440 | data:{"shared":{"these":"strings","are":"shared"},"count":"22","const":"const string","count_int":22}

sh.txt

$ git clone -b v5.13.5 https://github.com/bblanchon/ArduinoJson
$ cd ArduinoJson
...get runme.cpp here...
$ g++ -I./ -o runme runme.cpp
$ ./runme
{"shared":{"these":"strings","are":"shared","and":"this"}}
{"shared":{"these":"strings","are":"shared","and":"this"}}