Establish ODBC connections

Use these handle types to establish an ODBC connection.

SQLAllocHandle with SQL_HANDLE_ENV as the handle type

Allocates memory for an environment handle.
- Identifies storage for global information:
  - Valid connection handles
  - Current^® active connection handles
  - Variable type HENV
Must be called by application prior to calling any other ODBC function.
Variable type HENV is defined by ODBC in the SQL.H header file provided by the C programming language compiler or by the ODBC Software Development Kit (SDK).
The header file contains a type definition for a far pointer:
```
  typedef void far * HENV
```

In C programming language this statement is coded:

SQLRETURN rc;
HENV henv;

rc = SQLAllocHandle(SQL_HANDLE_ENV, SQL_NULL_HANDLE, &henv);

In Visual Basic, this statement is coded:
```
Dim henv As long
SQLAllocEnv(henv)
```

SQLAllocHandle with SQL_HANDLE_DBC as the handle type

Allocates memory for an connection handle within the environment.
- Identifies storage for information about a particular connection.
  - Variable type HDBC
  - Application can have multiple connection handles.
Application must request a connection handle prior to connecting to the data source.

In C, this statement is coded:

HDBC hdbc;

rc = SQLAllocHandle(SQL_HANDLE_DBC, henv, &hdbc);

In Visual Basic, this statement is coded:

Dim hdbc As long
SQLAllocConnect(henv,hdbc)

SQLSetEnvAttr

Allows an application to set attributes of an environment.
To be considered an ODBC 3.x application, you must set the SQL_ATTR_ODBC_VERSION to SQL_OV_ODBC3 prior to allocating a connection handle.

In C, this statement is coded:

rc = SQLSetEnvAttr(henv, SQL_ATTR_ODBC_VERSION, (SQLPOINTER) SQL_OV_ODBC3, SQL_IS_UINTEGER);

SQLConnect

Data source is coded into application.

In C, this statement is coded:

SQLCHAR source[ ] = "myDSN";
SQLCHAR uid[ ] = "myUID";
SQLCHAR pwd[ ] = "myPWD";

rc = SQLConnect(hdbc, source, SQL_NTS, uid, SQL_NTS, pwd, SQL_NTS);

Note: SQL_NTS indicates that the parameter string is a null-terminated string.

SQLDriverConnect