Re: [sqlite] sqlite_column_text converting result to a c++ string

[Jay Sprenkle]

On 10/17/05, Terry MacDonald <[EMAIL PROTECTED]> wrote:
> Hi,
>
> New to the list, so apologies if this has already been answered, I just
> can't find anything on my searches.
>
> I am writings something in C++ and I am also using the
> prepare/step/finalize approach to retrieve values from the sqlite
> database: no callbacks - messy in C++.
>
> There may be a simple answer to this but HOW do I get my return value
> from using sqlite_column_text (a const unsigned char*) into a c++ string?
>
> example...
>
>    string zName = sqlite3_column_text(pStmt,0) ;

I did it this way:
char* Sqlite::Column( const unsigned int Index )
  {
    char* p = (char*) sqlite3_column_text( pStmt, Index );
    return (char*) ( p ? p : "" );
  }

This checks for null column return values and returns an empty string.
I return everything as strings and handle conversion at a higher level.

I wrote a wrapper around sqlite for C++. I execute a query and return
the result set as an STL vector. It won't work for huge result sets because
it uses a lot of memory, but I seldom ever run a select against anything that
large anyway. For user interaction more than a page of results is generally
wasted.

Here are the wrapper class declarations:

//---------------------------------------------------------------------------
// a returned row from a query
// consists of a pair<string,string> returning column name and value
// operator() returns value given the column name
//---------------------------------------------------------------------------
class SqliteRow : public multimap<string,string>
  {
  public:
    const string  operator()( const string& key );
    void          operator+=( const pair<string,string>& column );

    void          dump();
  };

//---------------------------------------------------------------------------
// a returned set from a query
// consists of a vector of rows
//---------------------------------------------------------------------------
class SqliteSet : public vector<SqliteRow>
  {
  public:
    void          operator+=( const SqliteRow& row );

    void          dump();
  };

//---------------------------------------------------------------------------
// Sqlite wrapper
//---------------------------------------------------------------------------
class Sqlite
  {
    public:
      Sqlite( const string& filename );
      ~Sqlite();

      unsigned int              Changes();
      char*                     Column( const unsigned int Index );
      const char*               ColumnName( const unsigned int Index );

      SqliteRow                 ExecSingle( const string& sql );
      SqliteSet                 Select( const string& sql );
      unsigned int              Insert( const string& sql );
      unsigned int              Delete( const string& sql );
      unsigned int              Update( const string& sql );

      sqlite3*      db;
      sqlite3_stmt *pStmt;
    private:
      bool                      Prep( const string& sql );
      void                      Finalize();
      void                      Bind( const unsigned int Index, const
string* column );
      void                      Bind( const unsigned int Index, const
DateTime* column );
      int                       Step();

      SqliteRow                 Row();
  };