Question

I have the following class declaration:

class DEMData
{
private:
    int bitFldPos;
    int bytFldPos;
    const char* byteOrder;
    const char* desS;
    const char* engUnit;
    const char* oTag;
    const char* valType;
    int index;
public:
    DEMData();
    //DEMData(const DEMData &d);
    void SetIndex(int index);
    int GetIndex() const;
    void SetValType(const char* valType);
    const char* GetValType() const;
    void SetOTag(const char* oTag);
    const char* GetOTag() const;
    void SetEngUnit(const char* engUnit);
    const char* GetEngUnit() const;
    void SetDesS(const char desS[]);
    const char GetDesS() const;
    void SetByteOrder(const char* byteOrder);
    const char* GetByteOrder() const;
    void SetBytFldPos(int bytFldPos);
    int GetBytFldPos() const;
    void SetBitFldPos(int bitFldPos);
    int GetBitFldPos() const;
    friend std::ostream &operator<<(std::ostream &stream, DEMData d);
    //~DEMData();
};

I am creating a vector to hold objects of the above type like so:

vector<DEMData> dems;

If I were to push_back 100 objects into this vector, then all 100 objects will have the exact same values as the 100th element.

Below is the code snippet:

DEMData demData;
  for (i = 0; attr[i]; i += 2)
  {
      if(strcmp(attr[i],"BitFldPos") == 0)
      {
      demData.SetBitFldPos(*attr[i + 1] - '0');
      }
      else if(strcmp(attr[i],"BytFldPos") == 0)
      {
        char* pEnd;
        int tmp = strtol(attr[i + 1],&pEnd,10);
        demData.SetBytFldPos(tmp);
      }
      else if(strcmp(attr[i],"ByteOrder") == 0)
      {
        demData.SetByteOrder(attr[i + 1]);
      }
      else if(strcmp(attr[i],"DesS") == 0)
      {
      demData.SetDesS(attr[i + 1]);
      }
      else if(strcmp(attr[i],"EngUnit") == 0)
      {
        demData.SetEngUnit(attr[i + 1]);
      }
      else if(strcmp(attr[i],"OTag") == 0)
      {
        demData.SetOTag(attr[i + 1]);
      }
      else if(strcmp(attr[i],"ValTyp") == 0)
      {
        demData.SetValType(attr[i + 1]);
      }
      else if(strcmp(attr[i],"idx") == 0)
      {
        char* pEnd;
        int tmp = strtol(attr[i + 1],&pEnd,10);
        demData.SetIndex(tmp);
      }
  }

  // Insert the data in the vector.
  dems.push_back(demData);

Why would all elements have the same values?

Answer 1

push_back() makes a copy internally, but your DEMData class has no copy constructor, so all of the elements in the vector end up pointing to the same data. When you modify one, you modify all. Since the last element is modified last, you get all of the previous elements mirroring the last one.

HTH