SQLGetData issues using C++ and SQL Native Client - c++

Question

I have a C++ application that uses SQL Native Client to connect to a MS SQL Server 2000.
I am trying to retrieve a result from a TEXT column containing more data than the buffer initially allocated to it provides. To clarify my issue, I'll outline what I'm doing (code below):
allocate buffer of 1024 bytes use
bind buffer to column using SQLBindColumn
execute a SELECT query using SQLExecute
iterate through results using SQLFetch
SQLFetch was unable to return the entire result to my buffer: I'd like to use SQLGetData to retrieve the entire column value
The above order of operations presents a problem: SQLGetData does not work on bound columns in my driver.
A working solution is to use the SQL_DATA_AT_EXEC flag as illustrated by the code below.
Begin code:
#include <windows.h>
#include <sql.h>
#include <sqlext.h>
#include <sqltypes.h>
#include <sqlncli.h>
#include <cstdio>
#include <string>
const int MAX_CHAR = 1024;
bool test_retcode( RETCODE my_code, const char* my_message )
{
bool success = ( my_code == SQL_SUCCESS_WITH_INFO || my_code == SQL_SUCCESS );
if ( ! success )
{
printf( "%s", my_message );
}
return success;
}
int main ( )
{
SQLHENV EnvironmentHandle;
RETCODE retcode = SQLAllocHandle( SQL_HANDLE_ENV, SQL_NULL_HANDLE, &EnvironmentHandle );
test_retcode( retcode, "SQLAllocHandle(Env) failed!" );
retcode = SQLSetEnvAttr( EnvironmentHandle, SQL_ATTR_ODBC_VERSION, (SQLPOINTER) SQL_OV_ODBC3, SQL_IS_INTEGER );
test_retcode( retcode, "SQLSetEnvAttr(ODBC version) Failed" );
SQLHDBC ConnHandle;
retcode = SQLAllocHandle( SQL_HANDLE_DBC, EnvironmentHandle, &ConnHandle );
test_retcode( retcode, "Could not allocate MS SQL 2000 connection handle." );
SQLSMALLINT driver_out_length;
retcode = SQLDriverConnect( ConnHandle,
NULL, // we're not interested in spawning a window
(SQLCHAR*) "DRIVER={SQL Native Client};SERVER=localhost;UID=username;PWD=password;Database=Test;",
SQL_NTS,
NULL,
0,
&driver_out_length,
SQL_DRIVER_NOPROMPT );
test_retcode( retcode, "SQLConnect() Failed" );
SQLHSTMT StatementHandle;
retcode = SQLAllocHandle(SQL_HANDLE_STMT, ConnHandle, &StatementHandle);
test_retcode( retcode, "Failed to allocate SQL Statement handle." );
char* buffer = new char[ MAX_CHAR ];
SQLINTEGER length = MAX_CHAR - 1;
// -- Bind Block
retcode = SQLBindCol( StatementHandle,
1,
SQL_C_CHAR,
(SQLPOINTER) NULL,
(SQLINTEGER) SQL_DATA_AT_EXEC,
&length );
test_retcode( retcode, "Failed to bind column." );
// -- End Bind Block
retcode = SQLExecDirect( StatementHandle, (SQLCHAR*) "SELECT VeryLong FROM LongData", SQL_NTS );
test_retcode( retcode, "SQLExecDirect failed." );
// -- Fetch Block
retcode = SQLFetch( StatementHandle );
if ( retcode != SQL_SUCCESS && retcode != SQL_SUCCESS_WITH_INFO && retcode != SQL_NO_DATA )
{
printf( "Problem fetching row.\n" );
return 9;
}
printf( "Fetched data. length: %d\n", length );
// -- End Fetch Block
bool sql_success;
std::string data;
RETCODE r2;
do
{
r2 = SQLGetData( StatementHandle, 1, SQL_C_CHAR, buffer, MAX_CHAR, &length );
if ( sql_success = test_retcode( r2, "SQLGetData failed." ) )
{
data.append( buffer );
}
else
{
char* err_msg = new char[ MAX_CHAR ];
SQLSMALLINT req = 1;
SQLCHAR state[6];
SQLINTEGER error;
SQLINTEGER output_length;
int sql_state = SQLGetDiagRec( SQL_HANDLE_STMT, StatementHandle, req, state, &error, (SQLCHAR*) err_msg, (SQLINTEGER) MAX_CHAR, (SQLSMALLINT*) &output_length );
// state is: 07009, error_msg: "[Microsoft][SQL Native Client]Invalid Descriptor Index"
printf( "%s\n", err_msg );
delete err_msg;
return 9;
}
}
while ( sql_success && r2 != SQL_SUCCESS );
printf( "Done.\n" );
return 0;
}

Answer 1

Try to put SQLBindCol after SQLExecDirect.
For TEXT column use
retcode = SQLBindCol( StatementHandle, 1, SQL_C_CHAR,
(SQLPOINTER) NULL, (SQLINTEGER) SQL_DATA_AT_EXEC, &length );
in this way you can repeat SQLGetData to read entire TEXT data in multiple pieces