Run-Time Check Failure #2 - Stack around the variable 'files' was corrupted.

[circusjoker06]

int main(){
  Json::Reader reader;
  try
  {
    Json::Value root;

    const char* str2 = "{\"uploadid\": \"UP000000\",\"code\":-2105368552146909364,\"msg\": \"\",\"files\":[]}";

    if (reader.parse(str2, root))

    {

      string upload_id = root["uploadid"].asString();

      //int code = root["code"].asInt();

      string code =root["code"].asString();
      string msg = root["msg"].asString();
      Json::Value files =root["files"];
      {
        cout<<"files empty"<<endl;
      }
      cout<<root.size()<<" "<<upload_id<<" "<<code<<" "<<msg<<endl;
    }

  }
  catch(std::exception e)
  {
    // (1) it will catch the error show show
    cerr << e.what() << endl;
  }
  catch(std::out_of_range e)
  {
    // (2) this will also catch the same error if (1) was not there but could
    // get you more details if you wanted since its more specific but i have
    // not digged into it further
    cerr << e.what() << endl;
  }
  catch(...)
  {
    // (3) just for sanity check if first two didn't catch it
    cerr << "something went wrong";
  }
}

[circusjoker06]

error：Run-Time Check Failure #2 - Stack around the variable 'files' was corrupted.

[cdunn2001]

Works for me, on a recent MacAir with up-to-date o/s and compiler. Try the tip of the master branch.

[sergiy80]

@cdunn2001 ,
I could reproduce this. This happens because of struct packing size of json source files differ from packing size of my source files where json.h is included.
I am using VS 2013.
To reproduce build jsoncpp (I use amalgamated version) as a static lib with packing size 8 (default in VS2013). Use this static lib in another c++ project with packing size 4, 2 or 1, or just change packing size before including json.h. Start - got debug error from VS.

Also note sizeof(Json::StreamWriterBuilder) is changing depending on active packing size. I have 28 bytes - for sizes 1,2,4, and 32 bytes - for 8 and 16.
I thin this is the reason of the error.

To fix: add pragma pack guards in all jsoncpp headers, so that jsoncpp code does not depend on external packing size.
This also can be a reason of issues like: #391, #338

Sample is below:

#pragma pack(push, 2)
#include "json/json.h"
#pragma pack(pop)

void Run()
{
	std::cout << "Json::Value sizeof = " << sizeof(Json::Value) << std::endl;
	std::cout << "Json::StreamWriterBuilder sizeof = " << sizeof(Json::StreamWriterBuilder) << std::endl;

	Json::StreamWriterBuilder builder;
	std::unique_ptr<Json::StreamWriter> writer(builder.newStreamWriter());
	Json::Value v;
	v["val1"] = 123;
	writer->write(v, &std::cout);
	std::cout << std::endl;
}

[cdunn2001]

@sergiy80, thanks for the analysis. This seems like a good idea. Would you like to submit the pull-request?