Question

I retrieve numeric/decimal/money column values from SQL Server database as SQL_NUMERIC_STRUCT structures. Now I have to convert it to double for internal processing, and to string for GUI output. How can this be done?

Answer 1

Here is a good start. It doesn’t convert everything that you want to convert, but you can use the idea and algorithm to do arbitrary conversion with some simple mods:

DWORD g_Denominators[10]={1,10,100,1000,10000,100000,1000000,10000000,
                          100000000,1000000000};

void FetchDecimalValue(Fraction::NumeratorType &numerator, 
                       Fraction::DenominatorType &denominator,
                       const SQL_NUMERIC_STRUCT &src)
{
  numerator=0;
  denominator=1;
  DWORDLONG byteDenominator=1;

  for (size_t valIdx=0;valIdx<SQL_MAX_NUMERIC_LEN;++valIdx)
  {
    numerator+=src.val[valIdx]*byteDenominator;
    byteDenominator<<=8UI64;
  }

  // Is the NUMERIC negative?
  if (src.sign==0)
    numerator=-numerator;

  denominator=g_Denominators[src.scale];
}

You can easily create a double out of the resulting numerator and denominator by dividing the former by the later. Also, to create a string, you can always resort to sprintf or for a more C++ way, the double formatter of ostringstream.