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Trying to compile this code fails because the FileStream class (like all other public FCL classes) does not have a copy constructor. Even if there were a copy constructor, the expression would end up in two FileStream objects, and the lifetime rules would be even more complicated. Visual C++ comes with a special helper template, msclr::auto_handle, which can provide a solution to this problem. This template is defined in the header file msclr/auto_handle.h. The auto_handle template provides exactly the same service to tracking handles that the STL s auto_ptr provides for native pointers. Both helpers provide a scope-based deletion of an object. The STL s auto_ptr can automatically delete objects on the native heap, whereas auto_handle is used for objects on the managed heap. Like auto_ptr, the auto_handle template is only useful in special use cases. To use auto_handle correctly, it is necessary to know these use cases and understand the philosophy of this helper. The following code shows the most obvious use case for auto_handle: { // a new scope starts here // auto_handle variable wraps tracking FileStream reference auto_handle<FileStream> fs = GetFile(); // ...use auto_handle here } // when auto_handle leaves scope, FileStream object will be disposed msclr::auto_handle<T> is a template for a ref class that wraps a tracking handle of type T^. In its destructor, it deletes the managed object that the wrapped tracking handle refers to. Here is an extract of this template that shows how the automatic destruction is implemented: namespace msclr { template<typename T> ref class auto_handle { // the wrapped object T^ m_handle; bool valid() { // see if the managed resource is in the invalid state. return m_handle != nullptr; } public: ... other members ... ~auto_handle() { if( valid() ) { delete m_handle;

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Several important data dictionary views relate to space and storage issues. When you want to monitor or change storage at the data file or the tablespace level, you ll most likely use one or a combination of these views. In the following sections you ll look at how you can use these views to manage space in the database.

Extents are a collection of contiguous Oracle data blocks, and they re the smallest units with which you can allocate space to various database objects. The DBA_EXTENTS view is extremely useful for finding out the number of extents your database objects have, and also for getting alerts before you hit a maximum extents barrier. Listing 23-13 shows the structure of the DBA_EXTENTS view. Listing 23-13. The DBA_EXTENTS View SQL> DESC DBA_EXTENTS Name Null Type ----------------------------------------OWNER VARCHAR2(30) SEGMENT_NAME VARCHAR2(81) PARTITION_NAME VARCHAR2(30) SEGMENT_TYPE VARCHAR2(18) TABLESPACE_NAME VARCHAR2(30) EXTENT_ID NUMBER FILE_ID NUMBER BLOCK_ID NUMBER BYTES NUMBER BLOCKS NUMBER RELATIVE_FNO NUMBER SQL> You can use the DBA_EXTENTS view in combination with several other data dictionary views to help manage extent issues, as shown in the query in Listing 23-14. The results of the query indicate that there s no segment with more than 20 extents in it. The number 20 is arbitrary you can replace it with any reasonable number of extents. Listing 23-14. Using the DBA_EXTENTS View SQL> SELECT x.segment_name, 2 x.segment_type, 3 sum(x.bytes/1024/1024) megabytes, 4 count(x.bytes) count, 5 x.tablespace_name 6 FROM DBA_EXTENTS x, 7 dba_tables t, 8 dba_indexes i 9 WHERE x.segment_name in ('TABLE','INDEX') 10 AND x.owner = t.owner(+) 11 AND x.owner=i.owner(+) 12 GROUP BY 13. x.OWNER,x.SEGMENT_NAME,x.SEGMENT_TYPE,x.TABLESPACE_NAME 14 HAVING COUNT(x.bytes) >= 20 15* ORDER BY 1,2; no rows selected SQL>

In UNIX shell scripting there are both internal operators that allow you to test attributes or to compare values, and a /usr/bin/test system call. Please refer to Appendix A for more specific information. The following two comparison examples are among the most common forms: