Article ID: 135840
Article Last Modified on 6/12/2001
APPLIES TO
- Microsoft Open Database Connectivity 2.0
- Microsoft Visual Basic 3.0 Professional Edition
This article was previously published under Q135840
3.00 2.00
WINDOWS
kbprg kbcode
SUMMARY
This sample Visual Basic (VB) code illustrates the use of the ODBC API call SQLBindParameter() with a VB string variable. It has been kept as simple as possible with a minimal amount of code and declarations.
For more information on calling Windows APIs from Visual Basic, refer to the document "Ten Commandments for Accessing the Windows API" written by Daniel Appleman of Desaware and available on the Microsoft Developer Network (MSDN) Level 1 CD.
MORE INFORMATION
Declarations required to call ODBC API from VB 3.0:
Declare Function GetFocus Lib "User" () As Integer
Declare Function GetParent Lib "User" (ByVal hWnd%) As Integer
Declare Function SQLAllocConnect Lib "odbc.dll" (ByVal henv&, phdbc&)
As Integer
Declare Function SQLAllocEnv Lib "odbc.dll" (phenv&) As Integer
Declare Function SQLAllocStmt Lib "odbc.dll" (ByVal hdbc&, phstmt&) As
Integer
Declare Function SQLDisconnect Lib "odbc.dll" (ByVal hdbc&) As Integer
Declare Function SQLError Lib "odbc.dll" (ByVal henv&, ByVal hdbc&,
ByVal hstmt&, ByVal szSqlState$, pfNativeError&, ByVal szErrorMsg$,
ByVal cbErrorMsgMax%, pcbErrorMsg%) As Integer
Declare Function SQLExecDirect Lib "odbc.dll" (ByVal hstmt&, ByVal
szSqlStr$, ByVal cbSqlStr&) As Integer
Declare Function SQLFetch Lib "odbc.dll" (ByVal hstmt&) As Integer
Declare Function SQLFreeConnect Lib "odbc.dll" (ByVal hdbc&) As Integer
Declare Function SQLFreeEnv Lib "odbc.dll" (ByVal henv&) As Integer
Declare Function SQLFreeStmt Lib "odbc.dll" (ByVal hstmt&, ByVal
fOption%) As Integer
You should pay particular attention to the declaration of any string variable that will need to be passed to ODBC.DLL. This includes rgbValue in both SQLBindParameter() and SQLGetData(). The declaration should be "rgbValue as Any" to work. This is the most flexible way to declare a function variable for a Windows DLL function that will be passed from a VB program in a Windows DLL because it allows for both string and numeric values to be passed. When a string value is passed from a VB program to the Windows DLL and the DLL call expects a 'char *', then the VB program should declare the variable being passed as a VB String variable, and then pass it with the ByVal indicator. This is what is shown in the example here. If the VB variable to be passed had been a numeric value, then the variable that would be passed could be declared as long or integer, and during the call to the DLL, the variable would go into the call without the ByVal modifier.
The reason this happens is that in all cases, the C function expects a pointer to a memory location. From VB's perspective, a String variable refers to a pointer to a pointer to a memory location containing a string. This is why ByVal used in front of the variable during the function call gives a pointer to a memory location containing a string. On the other hand, a numeric variable in VB refers to a pointer to a memory location containing a numeric value. That is why the ByVal modifier is not necessary for the function call when a numeric VB variable is being passed in.
Declare Function SQLGetData Lib "odbc.dll" (ByVal hstmt&, ByVal
icol%, ByVal fCType%, rgbValue As Any, ByVal cbValueMax&, pcbValue As
Long) As Integer
Declare Function SQLBindParameter Lib "odbc.dll" (ByVal hstmt&, ByVal
ipar%, ByVal fParamType%, ByVal fCType%, ByVal fSqlType%, ByVal
cbColDef&, ByVal ibScale%, rgbValue As Any, ByVal cbValueMax&,
pcbValue As Long) As Integer
Declare Function SQLDriverConnect Lib "odbc.dll" (ByVal hdbc&, ByVal
hWnd%, ByVal szCSIn$, ByVal cbCSIn%, ByVal szCSOut$, ByVal cbCSMax%,
cbCSOut%, ByVal fDrvrComp%) As Integer
Declare Function SQLParamData Lib "odbc.dll" (ByVal hstmt&, prgbValue
As Any) As Integer
Declare Function SQLPutData Lib "odbc.dll" (ByVal hstmt&, rgbValue As
Any, ByVal cbValue&) As Integer
Const SQL_ERROR = -1
Const SQL_C_DEFAULT = 99
Const SQL_CHAR = 1
Const SQL_C_CHAR = 1
Const SQL_NEED_DATA = 99
Const SQL_LONGVARCHAR = -1
Const SQL_BINARY = -2
Const SQL_VARBINARY = -3
Const SQL_LONGVARBINARY = -4
Const SQL_C_BINARY = SQL_BINARY
Const SQL_DRIVER_PROMPT = 2
Const SQL_LEN_DATA_AT_EXEC_OFFSET = -100
Sub Command3D1_Click()
This sample VB code illustrates the use of the ODBC API call SQLBindParameter(). It has been kept as simple as possible with a minimal amount of code and declarations.
Dim henv As Long
Dim hdbc As Long
Dim hstmt As Long
Dim nstatus%
Dim buffer As String
Dim param As String
nstatus = SQLAllocEnv(henv)
nstatus = SQLAllocConnect(henv, hdbc)
If (nstatus = SQL_ERROR) Then
MsgBox "Couldn't allocate memory for connection"
End If
The parameters passed to SQLDriverConnect() after the second one are not really used for anything. The call expects the variables as output variables so we pass them to the call to problems.
nstatus = SQLDriverConnect(hdbc, GetParent(GetFocus()), S$,
Len(S$), Server, Len(Server), cbOut%, SQL_DRIVER_PROMPT)
If (nstatus = SQL_ERROR) Then
MsgBox "Couldn't connect"
End If
In this sample, you are connecting to a SQL Server database and define this table:
CREATE TABLE model01 (col1 char(30),col2 char(30))
after you have executed the following insert statement:
INSERT INTO model01 VALUES ("Kate Moss","Elite")
For simplicity, assume only one row in the table.
sSQLString = "Select * from model01 where col2 = ?"
leng = Len(sSQLString)
nstatus = SQLAllocStmt(hdbc, hstmt)
If (nstatus = SQL_ERROR) Then
MsgBox "Couldn't allocate memory for statement"
End If
At this point, assign a value to the variable "param" that is going to be bound to the SQL statement via SQLBindParameter(). After this binding, the SQL statement becomes:
select * from model01 where col2 = 'Elite'
It is not a requirement of the VB programmer to put the single quotation marks into the parameter marker (param). This is handled by ODBC.
param = "Elite"
In this particular call to SQLBindParameter, you are binding a VB string variable to a column on the SQL Server database server that is a char(30). The '1' in the third parameter of this call indicates that this parameter is of type SQL_PARAM_INPUT. For more information, refer to the definition of fParamType in the description of SQLBindParameter() in the "Microsoft ODBC 2.0 Programmer's Reference and SDK Guide."
The sixth parameter, cbColDef, is indicating that you will be binding to a column that is 30 bytes long on SQL Server. This could also be determined with SQLColumns() but is assumed here to keep this example small and simple.
The 7th parameter (ibScale) is zero because Appendix D of the ODBC 2.0 Programmer's Reference states that this is the case for char datatypes. The 8th parameter is a pointer to the VB SQLGetData() and the VB variable "param". Note that the ByVal in the passing of the VB variable called buffer is very important for this call to succeed. The 9th parameter is 300 because you should not return more than 300 bytes through this parameter. And the final parameter indicates that the parameter is a null-terminated string (SQL_NTS as defined in C:\ODBCSDK\INCLUDE\SQL.H).
nstatus = SQLBindParameter(hstmt, 1, 1, SQL_C_CHAR, SQL_CHAR, 30,
0, ByVal param, 300, -3)
If (nstatus = SQL_ERROR) Then
MsgBox "error on Bind"
End If
Send the SQL statement, which is now in the form:
select * from model01 where col2 = 'Elite'
nstatus = SQLExecDirect(hstmt, sSQLString, leng)
If (nstatus = SQL_ERROR) Then
MsgBox "Error on execdirect"
End If
Fetch back the first row of data. To keep this example simple, assume that this is the only row of data in the table that is of concern and fetch that. Normally, you should keep calling SQLFetch() and SQLGetData() in a loop until SQLFetch() returns 100 as a return code(SQL_NO_DATA_FOUND as defined in SQL.H).
nstatus = SQLFetch(hstmt)
If (nstatus = SQL_ERROR) Then
MsgBox "Error on fetch"
End If
It is important to initialize the VB variable that is being passed into SQLGetData() to return the data that was just fetched back. Otherwise, it may not be returned correctly or at all.
buffer = String$(300, 0)
Bring the data returned to the client workstation via SQLFetch() into the VB program via SQLGetData() and the VB variable "buffer". Note that the ByVal in the passing of the VB variable called buffer is very important for this call to succeed.
nstatus = SQLGetData(hstmt, 1, SQL_C_CHAR, ByVal buffer, Len(buffer),
300
)
If (nstatus = SQL_ERROR) Then
MsgBox "Error on getdata"
End If
Print the data just fetched back onto the screen.
MsgBox "buffer contains => " + buffer
Here, do a quick cleanup of the environment. Notice that you do not need to call SQLFreeStmt():
nstatus = SQLDisconnect(hdbc)
nstatus = SQLFreeConnect(hdbc)
nstatus = SQLFreeEnv(henv)
MsgBox "Finished"
End Sub
Additional query words: 3.00 function odbcsdk ref
Keywords: KB135840
