Initializing CLI applications

Initializing CLI applications is part of the larger task of programming with CLI. The task of initializing CLI applications involves allocating environment and connection handles and then connecting to the data source.

To initialize the application:

1. Allocate an environment handle by calling SQLAllocHandle() with a HandleType of SQL_HANDLE_ENV and an InputHandle of SQL_NULL_HANDLE.
   For example:

   SQLAllocHandle (SQL_HANDLE_ENV, SQL_NULL_HANDLE, &henv);

   Use the allocated environment handle, returned in the *OutputHandlePtr argument (henv in the example), for all subsequent calls that require an environment handle.

2. Optional: Set environment attributes for your application by calling SQLSetEnvAttr() with the required environment attribute for each attribute you want set.

   Important: If you plan to run your application as an ODBC application, you must set the SQL_ATTR_ODBC_VERSION environment attribute using SQLSetEnvAttr(). Setting this attribute for applications that are strictly CLI applications is recommended but not required.

3. Allocate a connection handle by calling SQLAllocHandle() with a HandleType of SQL_HANDLE_DBC using the environment handle returned from Step 1 as the InputHandle argument.
   For example:

   SQLAllocHandle (SQL_HANDLE_DBC, henv, &hdbc);

   Use the allocated connection handle, returned in the *OutputHandlePtr argument (hdbc in the example), for all subsequent calls that require a connection handle.

4. Optional: Set connection attributes for your application by calling SQLSetConnectAttr() with the required connection attribute for each attribute you want set.
5. Connect to a data source by calling one of following functions with the connection handle you allocated in Step 3 for each data source you want to connect to:
   • SQLConnect(): basic database connection method. For example:

     SQLConnect (hdbc, server, SQL_NTS, user, SQL_NTS, password, SQL_NTS);

     where SQL_NTS is a special string length value that indicates the referenced string is null-terminated.
   • SQLDriverConnect(): extended connect function that allows additional connect options and offers Graphical User Interface support. For example:

     char * connStr = "DSN=SAMPLE;UID=;PWD=;";
     
     SQLDriverConnect (hdbc, (SQLHWND)NULL, connStr, SQL_NTS,
                       NULL, 0, NULL, SQL_DRIVER_NOPROMPT);

   • SQLBrowseConnect(): least common connection method that iteratively returns the attributes and attribute values for connecting to a data source. For example:

     char * connInStr = "DSN=SAMPLE;UID=;PWD=;";
     char outStr[512];
     
     SQLBrowseConnect (hdbc, connInStr, SQL_NTS, outStr,
                       512, &strLen2Ptr);