Read BLOB object from SQL Database

CBlobRecordset.cpp

#include "pch.h"
#include "CBlobRecordset.h"

CBlobRecordset::CBlobRecordset(CDatabase* db) : CRecordset(db) {
    szErrorMessage[0] = 0;
    nError = 0;
    szSQLState[0] = 0;
}

long CBlobRecordset::GetBlobData(int nField, LPVOID pBuffer, int nBufferSize)
{
    SQLLEN nActualLength;
    SQLRETURN r = ::SQLGetData(m_hstmt, (short)nField + 1, SQL_C_BINARY, pBuffer, nBufferSize, &nActualLength);

    if (r != SQL_SUCCESS && r != SQL_SUCCESS_WITH_INFO)
    {
        if (::SQLGetDiagRec(SQL_HANDLE_STMT, m_hstmt, 1, szSQLState, &nError, szErrorMessage, 100, NULL) == SQL_SUCCESS)
            ::AfxThrowDBException(r, m_pDatabase, m_hstmt);
    }
    return nActualLength;
}

CBlobRecordset.h

#pragma once
#include <afxdb.h>
/*

Example:

Read varchar(max) Data:

       CDatabase db;
        // , DATALENGTH(Document) 
        CString strCon = _T("Driver={ODBC Driver 17 for SQL Server};Server=DESKTOP-RQTGTIQ\\SQLEXPRESS;Database=test2;Uid=sa;Pwd=XXXX;");
        CString strSQL = _T("SELECT  DATALENGTH(Document) ,[Document]  FROM [myTable] where FileName='ConnectionManager.pdb'");

         db.OpenEx(strCon);
        CBlobRecordset rs(&db);
        rs.Open(CRecordset::forwardOnly, strSQL);
 
        CString strMessage ;
        int len;

        LPVOID   blobBuffer ;
           
        while (!rs.IsEOF())
        {
            rs.GetFieldValue((short)0, strMessage);
         
            int fieldLen = atoi(strMessage);

            blobBuffer = malloc(fieldLen+1);
           long datalenn =  rs.GetBlobData(1, blobBuffer, fieldLen+1);

            rs.MoveNext();

            free(blobBuffer);
        }

        rs.Close();
        db.Close();


*/

#ifdef CONNECTIONMANAGER_EXPORTS
#define LIB_API_EXPORT __declspec(dllexport)
#else
#define LIB_API_EXPORT __declspec(dllimport)
#endif

class LIB_API_EXPORT CBlobRecordset :  public CRecordset
{
public:
    CBlobRecordset(CDatabase *db = NULL);
    /// <summary>
    ///    Read varchar(max) field 
    /// </summary>
    /// <param name="nFieldID"></param>
    /// <param name="pBuffer"></param>
    /// <param name="nBufferSize"></param>
    /// <returns></returns>
    long GetBlobData(int nFieldID, LPVOID pBuffer, int nBufferSize);
    /// <summary>
    ///    Error  message ( ReadBLOBData )
    /// </summary>
    SQLCHAR szErrorMessage[100];
    /// <summary>
    ///   Error number ( ReadBLOBData )
    /// </summary>
    SQLINTEGER nError;
    /// <summary>
    ///    five-character SQLSTATE code (and terminating NULL) for the diagnostic ( ReadBLOBData )
    /// </summary>
    SQLCHAR szSQLState[10];


};