Properly load data from database into edit control so I can execute ADO query

Question

INTRODUCTION AND RELEVANT INFORMATION:

I have an MS Access 2007 database with a table that has string field and numerical one. The numerical field is of type double and can be negative or positive.

I use ADO to connect to the database and load its data into edit controls with SetDialogItemText API-edit controls are in the dialog box.

User can edit the values of existing data ( when saving changes I get data from edit controls with GetDialogItemText API ).

PROBLEM:

Everything works fine in my program if the user has English or US locale, but if the user selects European locale then my ADO string is incorrect and reports error.

This is expected since in the English version it has 2 parameters-string and a double but since Europeans use comma as a decimal point ( for example US 123.456 is 123,456 ) ADO interprets it as having 3 parameters instead of two-for example:

INSERT INTO table VALUES ( 'some string', 12.5 ); ---> US locale

INSERT INTO table VALUES ( 'some string', 12,5 ); ---> ERROR! 3 parameters instead 2

To explain more thoroughly:

Let us say that we have loaded data from database into edit controls using European locale:

First one holds string ( Some string ) and second one decimal number ( 123,456 ).

Let us say user changes the string value into Some other string and presses the Save button.

Now my code gets values from edit controls but the error must occur since I got 123,456 from the second edit control ( remember, user left decimal data unchanged ), and my ADO string is not properly configured since now it looks like this:

INSERT INTO table VALUES ( 'Some other string', 123,456 );-->ERROR! 3 parameters

MY QUESTION:

If the user has set the European locale, is there a way to load decimal values from MS Access 2007 database into edit control with comma changed into dot?

Or maybe I can somehow subclass edit control to change comma into dot?

User input can be limited to dot and letters by sublclassing the edit control so that is not the problem. I just want to load data from database properly, so my ADO string can be executed without error if user decides not to edit decimal data like in the example I described above.

Thank you.

Best regards.

Answer 1

There are two issues at play here. I will illustrate using two locales:

English (Canada) -- EN-CA: which uses . as the decimal separator
French (Canada) -- FR-CA: which uses , as the decimal separator

and tiny bits of VBScript code (as I don't have C++).

Issue 1: Conversion of decimal numbers to/from locale-aware strings.

The VBScript

x = 3/2
WScript.Echo x

displays 1.5 when the Windows locale is EN-CA, and it displays 1,5 when the Windows locale is FR-CA. That text is what you are seeing in your edit box.

Say the user leaves the string unchanged. Instead of trying to use the string representation of the decimal number you need to use a locale-aware method of converting the string back to an actual decimal number:

For EN-CA:

x = CDbl("1.5") + 1
WScript.Echo x

displays 2.5 indicating that the string "1.5" was successfully converted to a Double before adding 1.

For FR-CA:

x = CDbl("1,5") + 1
WScript.Echo x

displays 2,5 indicating that the string "1,5" was successfully converted to a Double before adding 1.

Summary: When you receive a text representation of a number from the user you need to convert (i.e., parse) that string to an actual numeric data type, and the parsing mechanism must be locale-aware.

Issue 2: Storing the number in the database.

The problem here is that Access SQL is not locale-aware; it only "speaks" US English. So if you try and "glue together" a SQL command under FR-CA

x = 3/2
sql = "INSERT INTO Table1 (DoubleField) VALUES (" & x & ")"
WScript.Echo sql

you get INSERT INTO Table1 (DoubleField) VALUES (1,5) and that fails, as you have discovered.

The solution here is to NOT "glue together" SQL commands (which is a Bad Thing anyway, because of SQL Injection vulnerabilities and other nuisances). Instead, use a parameterized query:

Option Explicit
Dim con  ' ADODB.Connection
Dim cmd  ' ADODB.Command
Dim prm  ' ADODB.Parameter
Dim x
Const adDouble = 5
Const adParamInput = 1

' test data:
'     the following statement is valid when 
'         the Windows locale uses "," as the decimal separator
x = CDbl("1,5")

Set con = CreateObject("ADODB.Connection")
con.Open _
        "Driver={Microsoft Access Driver (*.mdb, *.accdb)};" & _
        "Dbq=C:\__tmp\main.accdb;"
Set cmd = CreateObject("ADODB.Command")
cmd.ActiveConnection = con
cmd.CommandText = "INSERT INTO Table1 (DoubleField) VALUES (?)"
Set prm = cmd.CreateParameter("?", adDouble, adParamInput, , x)
cmd.Parameters.Append prm
cmd.Execute
Set prm = Nothing
Set cmd = Nothing
con.Close
Set con = Nothing