Establishing an ODBC Connection

Establish a connection for your application, before it can carry out any database operations.

Allocate an ODBC environment:

SQLHENV env; 
SQLRETURN retcode; 
retcode = SQLAllocHandle( SQL_HANDLE_ENV, SQL_NULL_HANDLE, &env );

Declare the ODBC version.
By declaring that the application follows ODBC version 3, SQLSTATE values and some other version-dependent features are set to the proper behavior.

For example:
```
retcode = SQLSetEnvAttr( env, SQL_ATTR_ODBC_VERSION,
   (void*)SQL_OV_ODBC3, 0);
```
If necessary, assemble the datasource or connection string.

Depending on your application, you can have a hard-coded datasource or connection string, or you can store it externally for greater flexibility.

Allocate an ODBC connection handle:

retcode = SQLAllocHandle( SQL_HANDLE_DBC, env, &dbc );

Before connecting, set any connection attributes that are required.
Some connection attributes must be set before establishing a connection, while others can be set either before or after.

For example:
```
retcode = SQLSetConnectAttr( dbc, SQL_AUTOCOMMIT,
   (SQLPOINTER)SQL_AUTOCOMMIT_OFF, SQL_IS_UINTEGER);
```

Call the ODBC connection function:

if (retcode == SQL_SUCCESS || retcode ==
   SQL_SUCCESS_WITH_INFO)
{
   printf( "dbc allocated\n" );
   retcode = SQLConnect( dbc, (SQLCHAR*) "MANGO", 
      SQL_NTS, (SQLCHAR*) "sa", SQL_NTS, 
      (SQLCHAR*) "", SQL_NTS );
   if (retcode == SQL_SUCCESS || retcode ==       SQL_SUCCESS_WITH_INFO)
      {
         // successfully connected.
      }
}

You can find a complete sample of establishing a connection in your installation directory.

Notes on Usage

Every string passed to ODBC has a corresponding length. If the length is unknown, you can pass SQL_NTS indicating that it is a Null Terminated String whose end is marked by the null character (\0).
Use the SQLSetConnectAttr function to control details of the connection. For example, this statement turns off ODBC autocommit behavior:

retcode = SQLSetConnectAttr( dbc, SQL_AUTOCOMMIT, 
   (SQLPOINTER)SQL_AUTOCOMMIT_OFF, SQL_IS_UINTEGER );

Many aspects of the connection can be controlled through the connection parameters.

For more information including a list of connection attributes, see SQLSetConnectAttr in the Microsoft ODBC Programmer's Reference.