Technical Information Database
TI186B.txt Comparison filters.
Category :General Programming
Platform :All
Product :BDE All
Description:
/*
This example shows how to set a filter on the first N
characters of a character field. To use this example, backup
the FILTER.C file in the BDE\EXAMPLES\SNIPIT directory. Copy
this file to FILTER.C in that directory. Then compile and
run SNIPIT, running the 'Cursor: Setting and Using filters'
example.
*/
// BDE - (C) Copyright 1994 by Borland International
// Filter.c
#include "snipit.h"
static const char szTblName[] = "customer";
static const char szTblType[] = szPARADOX;
//==============================================================
// Function:
// Filter();
//
// Description:
// This example shows how to use filters to limit the
// result set of a table. Filters perform a function
// similar to that of ranges, but more powerful
// operations are supported.
//==============================================================
void
Filter (void)
{
hDBIDb hDb; // Handle to the database.
hDBICur hCur; // Handle to the table.
pBYTE pcanExpr; // Structure containing
// filter info.
hDBIFilter hFilter; // Filter handle.
UINT16 uSizeNodes; // Size of the nodes in the
// tree.
UINT16 uSizeCanExpr; // Size of the header
// information.
UINT16 uSizeLiterals; // Size of the literals.
UINT16 uTotalSize; // Total size of the filter
// expression.
UINT32 uNumRecs = 10; // Number of records to
// display.
CANExpr canExp; // Contains the header
// information.
UINT16 Nodes[] = // Nodes of the filter
// tree.
{
// Offset 0
nodeCOMPARE, // canCompare.nodeClass
canEQ, // canCompare.canOp
1, // canCompare.bCaseInsensitive
5, // canCompare.iParialLen (0 if
// full length)
12, // canBinary.iOperand1
20, // canBinary.iOperand2
// Offsets in the Nodes array
// Offset 12
nodeFIELD, // canField.nodeClass
canFIELD, // canField.canOp
2, // canField.iFieldNum
0, // canField.iNameOffset: szField
// is the literal at offset 0
// Offset 20
nodeCONST, // canConst.nodeClass
canCONST, // canConst.canOp
fldZSTRING, // canConst.iType
6, // canConst.iSize
5 // canConst.iOffset: szConst is
// the literal at offset
// strlen(szField) + 1
};
// Name of the field for the third node of the tree.
CHAR szField[] = "NAME";
// Value of the constant for the second node of the tree.
CHAR szConst[] = "OCEAN";
// Return value from IDAPI functions.
DBIResult rslt;
Screen("*** Filter Example ***\r\n");
BREAK_IN_DEBUGGER();
Screen(" Initializing IDAPI...");
if (InitAndConnect(&hDb) != DBIERR_NONE)
{
Screen("\r\n*** End of Example ***");
return;
}
Screen(" Setting the database directory...");
rslt = DbiSetDirectory(hDb, (pCHAR) szTblDirectory);
ChkRslt(rslt, "SetDirectory");
Screen(" Open the %s table...", szTblName);
rslt = DbiOpenTable(hDb, (pCHAR) szTblName,
(pCHAR) szTblType, NULL, NULL, 0,
dbiREADWRITE, dbiOPENSHARED, xltFIELD,
FALSE, NULL, &hCur);
if (ChkRslt(rslt, "OpenTable") != DBIERR_NONE)
{
CloseDbAndExit(&hDb);
Screen("\r\n*** End of Example ***");
return;
}
// Go to the beginning of the table
rslt = DbiSetToBegin(hCur);
ChkRslt(rslt, "SetToBegin");
Screen("\r\n Display the %s table...", szTblName);
DisplayTable(hCur, uNumRecs);
uSizeNodes = sizeof(Nodes); // Size of the nodes.
// Size of the literals.
uSizeLiterals = strlen(szField) + 1 + strlen(szConst) + 1;
// Size of the header information.
uSizeCanExpr = sizeof(CANExpr);
// Total size of the filter.
uTotalSize = uSizeCanExpr + uSizeNodes + uSizeLiterals;
// Initialize the header information
canExp.iVer = 1; // Version.
canExp.iTotalSize = uTotalSize; // Total size of the
// filter.
canExp.iNodes = 3; // Number of nodes.
canExp.iNodeStart = uSizeCanExpr; // The offset in the
// buffer where the
// expression nodes
// start.
// The offset in the buffer where the literals start.
canExp.iLiteralStart = uSizeCanExpr + uSizeNodes;
// Allocate space for the filter expression.
pcanExpr = (pBYTE)malloc(uTotalSize * sizeof(BYTE));
if (pcanExpr == NULL)
{
Screen(" Could not allocate memory...");
DbiCloseCursor(&hCur);
CloseDbAndExit(&hDb);
Screen("\r\n*** End of Example ***");
return;
}
// Initialize the filter expression.
memmove(pcanExpr, &canExp, uSizeCanExpr);
memmove(&pcanExpr[uSizeCanExpr], Nodes, uSizeNodes);
memmove(&pcanExpr[uSizeCanExpr + uSizeNodes],
szField, strlen(szField) + 1); // First litteral
memmove(&pcanExpr[uSizeCanExpr + uSizeNodes +
strlen(szField) + 1],
szConst, strlen(szConst) + 1); // Second litteral
rslt = DbiSetToBegin(hCur);
ChkRslt(rslt, "SetToBegin");
Screen("\r\n Add a filter to the %s table which will"
" limit the records\r\n which are displayed"
" to those whose %s field starts with '%s'...",
szTblName, szField, szConst);
rslt = DbiAddFilter(hCur, 0L, 1, FALSE, (pCANExpr)pcanExpr,
NULL, &hFilter);
if (ChkRslt(rslt, "AddFilter") != DBIERR_NONE)
{
rslt = DbiCloseCursor(&hCur);
ChkRslt(rslt, "CloseCursor");
free(pcanExpr);
CloseDbAndExit(&hDb);
Screen("\r\n*** End of Example ***");
return;
}
// Activate the filter.
Screen(" Activate the filter on the %s table...",
szTblName);
rslt = DbiActivateFilter(hCur, hFilter);
ChkRslt(rslt, "ActivateFilter");
rslt = DbiSetToBegin(hCur);
ChkRslt(rslt, "SetToBegin");
Screen("\r\n Display the %s table with the filter"
" set...", szTblName);
DisplayTable(hCur, uNumRecs);
Screen("\r\n Deactivate the filter...");
rslt = DbiDeactivateFilter(hCur, hFilter);
ChkRslt(rslt, "DeactivateFilter");
Screen("\r\n Drop the filter...");
rslt = DbiDropFilter(hCur, hFilter);
ChkRslt(rslt, "DropFilter");
rslt = DbiCloseCursor(&hCur);
ChkRslt(rslt, "CloseCursor");
free(pcanExpr);
Screen(" Close the database and exit IDAPI...");
CloseDbAndExit(&hDb);
Screen("\r\n*** End of Example ***");
}
Reference:
7/15/98 3:24:21 PM
Last Modified: 01-SEP-99