当我尝试转换Int64时，poco库上的错误转换异常

Question

I wrote some code for parse JSON string. I got "Bad Cast Exception" sometimes. In My JSON string 1. 2. don't raise exception and 3. 4. raise exception.

A difference between two group is that 1. 2. 's BCodeW is in range long and 3. 4. 's BCodeW is in range Int64.

---

my environment is below.

• g++ (GCC) 4.4.7 20120313 (Red Hat 4.4.7-11)
• poco-1.6.0 (using Poco::JSON)
• CentOS release 6.6 (Final)

---

My JSON string example below.

1. {"y":37.56376,"x":126.97287,"poiY":37.563686111111,"poiX":126.97302222222,"jibunY":37.563805555556,"jibunX":126.97285833333, ,"poi":"...","jibun":"..."}
2. {"y":37.59771,"x":127.041493,"poiY":37.597605555556,"poiX":127.041725,"jibunY":37.597547222222,"jibunX":127.04176666667, ,"poi":"...","jibun":"..."}
3. {"y":36.760035,"x":127.250362,"poiY":36.759905555556,"poiX":127.25036111111,"jibunY":36.760119444444,"jibunX":127.25040833333, ,"poi":"...","jibun":"..."}
4. {"y":36.129513,"x":128.34381,"poiY":36.128672222222,"poiX":128.34373888889,"jibunY":36.129738888889,"jibunX":128.34425833333, ,"poi":"...","jibun":"..."}

---

My Code is below.

bool CUBIUtils::ParseAddressResult( llong& _BCodeW, char* _szPOI, char* _szJibun, char* _szAPIResult )
{
  JSON::Parser parser;
  try
  {
    JSON::Object::Ptr _object = parser.parse(_szAPIResult).extract<JSON::Object::Ptr>();
    if ( NULL == _object)
    {
      formatlog( LOG_ERROR, "JSON parsing failed");
      return false;
    }

    formatlog( LOG_DEBUG, "CUBIUtils::%s(%d) AddrSrc: %s", __func__, __LINE__, _szAPIResult);

    _BCodeW = 0;
    try
    {
      _BCodeW = _object->get("BCodeW").extract<Int64>();
    }
    catch(exception &_e)
    {
      _BCodeW = _object->get("BCodeW").extract<int>();
    }

    strcpy(   _szPOI, _object->get("poi").extract<std::string>().c_str());
    strcpy( _szJibun, _object->get("jibun").extract<std::string>().c_str());
  }
  catch(exception &e)
  {
    formatlog( LOG_ERROR, "CUBIUtils::%s(%d) JSON parsing Exception. %s", __func__, __LINE__, e.what());
    return false;
  }

  return true;
}

---

Var.h in Poco's source code says.

  /// Invoke this method to perform a safe conversion. /// /// Example usage: /// Var any("42"); /// int i = any.convert<int>(); /// /// Throws a RangeException if the value does not fit /// into the result variable. /// Throws a NotImplementedException if conversion is /// not available for the given type. /// Throws InvalidAccessException if Var is empty. 

---

Below Code works.

use convert<T>() instead of extract<T>()

Data type is different. "i", "l"

extract get data which are exactly match type.

_BCodeW = 0;
if ( _object->isNull("BCodeW"))
  cout << "BCodeW is NULL" << endl;
else
{
  Dynamic::Var _BCodeWVar = _object->get("BCodeW");
  cout << "Data Type is " << _BCodeWVar.type().name() << endl;

  _BCodeW = _BCodeWVar.convert<Int64>();
  cout << "BCodeW is " << _BCodeW << endl;
}

Answer 1

The problem here is not in the JSON parsing and/or data extraction. It is in the comparison line:

if (NULL == _object)

that line will result in BadCastException being thrown.

The reason is because the operator== resolves to

inline bool operator == (const Poco::Int32& other, const Var& da)

and conversion of Poco::JSON::Object::Ptr to Poco::Int32 throws.

Replace the offending line with

if (_object.isNull())

and all will be well.