C ++浮点到SQL Server DECIMAL正确转换

Question

I am creating an application in native c++ using odbc. I am calling on to a sql server stored procedure that has a decimal parameter. I am passing a float to that parameter. The code so far:

    SQLDECIMAL *sql_param = new SQLDECIMAL( param);
if( SQL_ERROR == ( result = SQLBindParameter( statement_handle, 5, SQL_PARAM_INPUT, SQL_C_FLOAT, SQL_DECIMAL, 12, 6, sql_param, 0, NULL ) ) ){
    std::wstring error = get_error_message( SQL_HANDLE_STMT, statement_handle );

    throw GenericException( error );
}

param is a float.

What gets stored on the table is always 0 instead of the real value which is 1.45. I'm guessing some conversion is taking place but I can't figured out the correct conversion. SQL_C_FLOAT -> SQL_DECIMAL?

Answer 1

In the reference :

SQLRETURN SQLBindParameter(
      SQLHSTMT        StatementHandle,
      SQLUSMALLINT    ParameterNumber,
      SQLSMALLINT     InputOutputType,
      SQLSMALLINT     ValueType,
      SQLSMALLINT     ParameterType,
      SQLULEN         ColumnSize,
      SQLSMALLINT     DecimalDigits,
      SQLPOINTER      ParameterValuePtr,
      SQLLEN          BufferLength,
      SQLLEN *        StrLen_or_IndPtr);
...

BufferLength
[Input/Output] Length of the ParameterValuePtr buffer in bytes.

You have specified BufferLength as zero. Looking here , you can see the length of decimal for different precision values:

Precision      StorageBytes
1-9             5
10-19           9
20-28           13
29-38           17

Therefore, you need to call method SQLBindParameter as:

SQLBindParameter( statement_handle, 1, SQL_PARAM_INPUT, SQL_C_FLOAT, SQL_DECIMAL, 12, 6, sql_param, 5, NULL )

Answer 2

The SQLDECIMAL is your problem. According to http://publib.boulder.ibm.com/infocenter/soliddb/v6r3/index.jsp?topic=/com.ibm.swg.im.soliddb.programmer.doc/doc/s0005314.c.data.types.html it is a unsigned char [f]. I suggest something like:

void bind_float(float* param) {
    SQLBindParameter( statement_handle, 5, SQL_PARAM_INPUT, SQL_C_FLOAT, SQL_DECIMAL, 12, 6, param, 0, NULL ) ) );
}

Answer 3

I got it. It shouldn't have been: SQLDECIMAL *sql_param = new SQLDECIMAL( param ); it should have been: SQLDECIMAL *sql_param = (SQLDECIMAL *) param;