FIX: CDatabase::ExecuteSQL() Fails with UNICODE Build (139759)
The information in this article applies to:
- The Microsoft Foundation Classes (MFC), when used with:
- Microsoft Visual C++, 32-bit Editions 4.0
This article was previously published under Q139759 SYMPTOMS
Trying to run a program that contains a call to CDatabase::ExecuteSQL()
that has been built for UNICODE results in a CDBException being thrown with
an error message from the ODBC driver. The message depends on the SQL
Statement and the ODBC driver. For example, trying to execute an INSERT
statement on a data source that uses the Microsoft Access ODBC driver
results in the following error message:
Invalid SQL statement;
expected 'DELETE', 'INSERT', 'PROCEDURE', 'SELECT', or 'UPDATE'.
State:37000,Native:-3500,Origin:
[Microsoft][ODBC Microsoft Access 7.0 Driver]
CAUSE
The SQL string passed to CDatabase::ExecuteSQL() is a UNICODE string, and
the ODBC API expects all arguments that are strings to be ASCII strings.
RESOLUTION
To work around this bug, you have to convert the string yourself, and then
cast the resultant ASCII string to an LPCTSTR when you pass it to
CDatabase::ExecuteSQL(). The cast is necessary because
CDatabase::ExecuteSQL() expects a wide character string.
For example, using the following code to delete all the records in a table
will fail in an MFC 4.0 program:
CString strSQL = _T("DELETE FROM Table1");
MyDatabase.ExecuteSQL(strSQL);
To make the code work, you need to use code similar to this code:
#include <winnls.h> // add this include for WideCharToMultiByte()
.
.
.
CString strSQL = _T("DELETE FROM Table1");
char* szAscii = new char[strSQL.GetLength() + 1];
WideCharToMultiByte(CP_ACP,0,strSQL,-1,
szAscii,strSQL.GetLength() + 1,NULL,NULL);
MyDatabase.ExecuteSQL((LPCTSTR)szAscii);
delete [] szAscii;
STATUS
Microsoft has confirmed this to be a bug in the Microsoft products
listed at the beginning of this article. This bug was corrected in
Visual C++ 4.1.
MORE INFORMATION
In general, you can use the MFC ODBC classes in UNICODE programs. The MFC
ODBC classes will handle the UNICODE/ASCII conversions for ODBC API calls.
CDatabase::ExecuteSQL() is missing this conversion support.
| Modification Type: | Major | Last Reviewed: | 10/24/2003 |
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| Keywords: | kbbug kbDatabase kbfix kbVC410fix KB139759 |
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