INF: How to Use SQL_C_NUMERIC Data Type with Numeric Data

• Microsoft Open Database Connectivity, version 3.0

SUMMARY

ODBC 3.0 introduces a new ODBC C data type, identified by SQL_C_NUMERIC, which allows applications to directly handle numeric data. The C buffer used has the type definition of SQL_NUMERIC_STRUCT, and is a structure with fields for storing the precision, scale, sign, and value of the numeric data. The value itself is stored as a scaled integer with the least significant byte beginning in the leftmost position.

Additional information regarding the format and use of SQL_NUMERIC_STRUCT is available in the ODBC 3.0 Programmer's Reference, in Appendix D (Data Types) in the "C Data Types" section.

MORE INFORMATION

WARNING: ANY USE BY YOU OF THE CODE PROVIDED IN THIS ARTICLE IS AT YOUR OWN RISK. Microsoft provides this code "as is" without warranty of any kind, either express or implied, including but not limited to the implied warranties of merchantability and/or fitness for a particular purpose.

The following sample program illustrates the use of SQL_C_NUMERIC by inserting 123.45 into a table defined with a column whose data type is numeric or decimal, precision 5 and scale 2. Comments are embedded in the code to explain the key points. The ODBC driver used to run this program must support ODBC 3.0 functionality.

#include <windows.h>
#include <sql.h>
#include <sqlext.h>

void main() {

   SQLHENV     henv = NULL;
   SQLHDBC     hdbc = NULL;
   SQLHSTMT   hstmt = NULL;

   SQL_NUMERIC_STRUCT     NumStr;
   SQLINTEGER                     cbNumStr = sizeof (NumStr);

   SQLAllocHandle(SQL_HANDLE_ENV, NULL, &henv);

   /* Set the ODBC behavior version. */
   SQLSetEnvAttr(henv,
         SQL_ATTR_ODBC_VERSION,
         (SQLPOINTER) SQL_OV_ODBC3,
         SQL_IS_INTEGER);

   SQLAllocHandle(SQL_HANDLE_DBC, henv, &hdbc);

   /* Substitute your own connection information */
   SQLConnect(hdbc,
      (SQLCHAR *) "MyDSN", 5,
      (SQLCHAR *) "UserID", 6,
      (SQLCHAR *) "Password", 8);

   SQLAllocHandle(SQL_HANDLE_STMT, hdbc, &hstmt);

   /*
      Set up the SQL_NUMERIC_STRUCT, NumStr, to hold "123.45".

      First, we need to scale 123.45 to an integer: 12345
      One way to switch the bytes is to convert 12345 to Hex:  0x3039
      Since the least significant byte will be stored starting from the
      leftmost byte, "0x3039" will be stored as "0x3930".

      The precision and scale fields are not used for input to the driver,
      only for output from the driver. The precision and scale will be set
      in the application parameter descriptor later.
   */

   NumStr.sign = 1;   /* 1 if positive, 2 if negative */

      memset (NumStr.val, 0, 16);
   NumStr.val [0] = 0x39;
   NumStr.val [1] = 0x30;

   /* SQLBindParameter needs to be called before SQLSetDescField */
   SQLBindParameter(hstmt,
          1,
          SQL_PARAM_INPUT,
          SQL_C_NUMERIC,
          SQL_NUMERIC,
          5,
          2,
          &NumStr,
          0,
          (SQLINTEGER *) &cbNumStr);

   /* Modify the fields in the implicit application parameter descriptor */
   SQLHDESC   hdesc = NULL;

   SQLGetStmtAttr(hstmt, SQL_ATTR_APP_PARAM_DESC, &hdesc, 0, NULL);
   SQLSetDescField(hdesc, 1, SQL_DESC_TYPE, (SQLPOINTER) SQL_C_NUMERIC, 0);
   SQLSetDescField(hdesc, 1, SQL_DESC_PRECISION, (SQLPOINTER) 5, 0);
   SQLSetDescField(hdesc, 1, SQL_DESC_SCALE, (SQLPOINTER) 2, 0);
   SQLSetDescField(hdesc, 1, SQL_DESC_DATA_PTR, (SQLPOINTER) &NumStr, 0);

   SQLExecDirect(hstmt,
         (SQLCHAR *) "INSERT INTO table (numeric_column) VALUES (?)",
         SQL_NTS);

   SQLFreeHandle(SQL_HANDLE_STMT, hstmt);

   SQLDisconnect (hdbc);

   SQLFreeHandle(SQL_HANDLE_DBC, hdbc);
   SQLFreeHandle(SQL_HANDLE_ENV, henv);

Keywords          : SSrvProg
Version           : Windows:3.0
Platform          : WINDOWS
Issue type        : kbhowto