SQLBindParameter to prepare for SQLPutData using C++ and SQL Native Client - c++

Question

I'm trying to use SQLBindParameter to prepare my driver for input via SQLPutData. The field in the database is a TEXT field. My function is crafted based on MS's example here:
http://msdn.microsoft.com/en-us/library/ms713824(VS.85).aspx.
I've setup the environment, made the connection, and prepared my statement successfully but when I call SQLBindParam (using code below) it consistently fails reporting: [Microsoft][SQL Native Client]Invalid precision value
int col_num = 1;
SQLINTEGER length = very_long_string.length( );
retcode = SQLBindParameter( StatementHandle,
col_num,
SQL_PARAM_INPUT,
SQL_C_BINARY,
SQL_LONGVARBINARY,
NULL,
NULL,
(SQLPOINTER) col_num,
NULL,
&length );
The above relies on the driver in use returning "N" for the SQL_NEED_LONG_DATA_LEN information type in SQLGetInfo. My driver returns "Y". How do I bind so that I can use SQLPutData?

Answer 1

Though it doesn't look just like the documentation's example code, I found the following solution to work for what I'm trying to accomplish. Thanks gbjbaanb for making me retest my input combinations to SQLBindParameter.
SQLINTEGER length;
RETCODE retcode = SQLBindParameter( StatementHandle,
col_num, // position of the parameter in the query
SQL_PARAM_INPUT,
SQL_C_CHAR,
SQL_VARCHAR,
data_length, // size of our data
NULL, // decimal precision: not used our data types
&my_string, // SQLParamData will return this value later to indicate what data it's looking for so let's pass in the address of our std::string
data_length,
&length ); // it needs a length buffer
// length in the following operation must still exist when SQLExecDirect or SQLExecute is called
// in my code, I used a pointer on the heap for this.
length = SQL_LEN_DATA_AT_EXEC( data_length );
After a statement is executed, you can use SQLParamData to determine what data SQL wants you to send it as follows:
std::string* my_string;
// set string pointer to value given to SQLBindParameter
retcode = SQLParamData( StatementHandle, (SQLPOINTER*) &my_string );
Finally, use SQLPutData to send the contents of your string to SQL:
// send data in chunks until everything is sent
SQLINTEGER len;
for ( int i(0); i < my_string->length( ); i += CHUNK_SIZE )
{
std::string substr = my_string->substr( i, CHUNK_SIZE );
len = substr.length( );
retcode = SQLPutData( StatementHandle, (SQLPOINTER) substr.c_str( ), len );
}

Answer 2

you're passing NULL as the buffer length, this is an in/out param that shoudl be the size of the col_num parameter. Also, you should pass a value for the ColumnSize or DecimalDigits parameters.
http://msdn.microsoft.com/en-us/library/ms710963(VS.85).aspx