Convert variant from recordset (with currency value) into properly formatted string

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I have a query that gets the value of the payed amount of money. This field is currency type, in MS Access database.

I need to display this value in textbox ( I am using C++ and raw WinAPI for GUI ), so I need to know how to convert _variant_ from recordset into proper string (1,200.55).

Here is an example ( remember, I use raw WinAPI and C++ for GUI ):

C++

SetDlgItemText(hDlg, IDC_EDIT11, 
    pRS->Fields->GetItem(L"PaidValue")->Value.bstrVal); // problem is this line

My textbox is empty when I run the program.

When I debug it, it reports no errors.

QUESTION:

How can I convert _variant_t into string ( 1,200.00 )?

Posted 10-Feb-15 17:30pm

AlwaysLearningNewStuff

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barneyman · Answer 1 · 2015-02-10T18:36:00

Won't the currency type be mapped to something a little less stringy? i.e. an R8? examine the

C++

Value->dblVal

component

As far as formatting it correctly, you have 4 locale items to determine (if you want to do it 'right')

1. currency symbol (LOCALE_SCURRENCY)
2. grouping (LOCALE_SMONGROUPING)
3. grouping seperator (LOCALE_SMONTHOUSANDSEP)
3. decimal seperator (LOCALE_SMONDECIMALSEP)
4. negation method (LOCALE_INEGCURR)

or just assume 3,comma grouping and . decimal (anglosphere type)

Easiest way is to print it to a string (%.2f) then carve it up manually to insert the comma at the right place

Jochen Arndt · Answer 2 · 2015-02-10T21:04:00

Solution 2

Currency values are stored as type CURRENCY in the cyVal member of the VARIANT[^] with variant type VT_CY. From the above link:

Quote:
A currency number is stored as 64-bit (8-byte), two's complement integer, scaled by 10,000 to give a fixed-point number with 15 digits to the left of the decimal point and 4 digits to the right. The value is in cyVal.

CURRENCY is defined as:

C++

typedef union FARSTRUCT tagCY {
    struct {
        unsigned long Lo;
        long          Hi;
    };
    LONGLONG int64;
} CY;

When using MFC, you can use the COleCurrency class which provides a format function. Without MFC you can implement similar functionality by checking how COleCurrency::Format is implemented (MFC source file olevar.cpp). It uses VarBstrFromCy[^] to convert the value to a BSTR.

Posted 10-Feb-15 21:04pm

Jochen Arndt

Comments

AlwaysLearningNewStuff 11-Feb-15 12:24pm

It did work, but it does not group thousands. I really need this functionality. I could use your solution to bet the string, but I do not know any function that formats it properly. Can you suggest one, since you are more experienced and better programmer than I am? Thank you for your help.

Jochen Arndt 11-Feb-15 12:55pm

There is no ready-to-use function.

With C++ you can specify the format (example at http://cplus.about.com/od/learning1/ss/cppnumbers_5.htm). This can be also used with std::ostringstream to write the string to memory.

With C you must write your own function. An example can be found at http://www.cprogramming.com/snippets/source-code/thousand-separator-example (is C++ but can be adapted to print to a buffer).
Another example: http://www.drdobbs.com/cpp/a-simple-function-for-formatting-currenc/232700238

To avoid rounding errors you should not convert the value to double but split the 64-bit value it into digits before and after comma (div 10,000 / mod 10,000) and print the parts separately.