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Mapping const unsigned char* to const unsigned char% would not be sufficient here, because the encryption key passed to the constructor of the native type contains more than one byte. The following code shows a better approach: namespace ManagedWrapper { public ref class SampleCipher { NativeLib::SampleCipher* pWrappedObject; public: SampleCipher(array<Byte>^ key); /* ... */ }; } In this constructor, both native arguments (pKey and nKeySizeInBytes) are mapped to a single argument of a managed array type. This is possible because the size of a managed array can be determined at runtime. The implementation of this constructor depends on the implementation of the native SampleCipher class. If the constructor of the native class internally copies the key that is passed via the argument pKey, you can use a pinned pointer to pass the key: SampleCipher::SampleCipher(array<Byte>^ key) { if (!key) throw gcnew ArgumentNullException("key"); pin_ptr<unsigned char> pp = &key[0]; pWrappedObject = new NativeLib::SampleCipher(pp, key->Length); } However, a pinned pointer cannot be used if the native SampleCipher class is implemented as follows: namespace NativeLib { class SampleCipher : public CryptoAlgorithm { const unsigned char* pKey; const int nKeySizeInBytes; public: SampleCipher(const unsigned char* pKey, int nKeySizeInBytes) : pKey(pKey), nKeySizeInBytes(nKeySizeInBytes) {} /* ... rest of the class can be ignored here ... */ }; }

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The feature shown in Listing 13-6 writing to an external table is an Oracle Database 10g external tables enhancement. Listing 13-6. Populating an External Table SQL> CREATE TABLE test_xt ORGANIZATION EXTERNAL( TYPE ORACLE_DATAPUMP DEFAULT DIRECTORY ext_data_dir LOCATION ('test_xt.dmp')) AS SELECT * FROM scott.dept; Note how the external table creation statement uses the SELECT * FROM . . . clause to write data from the scott.dept table to the external table (file). If your new external table contains some but not all of the columns of the table scott.dept, you use the appropriate SELECT statement instead of the SELECT * FROM statement.

Remember that when you load an Oracle table from an external table (data loading), you use the INSERT INTO . . . SELECT clause. When you populate an external table using Oracle table data (data unloading), you use the CREATE TABLE . . . AS SELECT clause.

If you now go look in the location specified for the default directory (ext_data_dir), you ll see the following: SQL> ls -altr Total 24 drwxr-xr-x -rw-r--r--rw-r-------

$ ls -l total 1484 -rw-rw-r-- 1 rbpeters rbpeters 1057862 Jun 7 18:21 37l5152.log -rw-rw-r-- 1 rbpeters rbpeters 449184 Jun 7 18:21 770tref.log -rw-rw-r-- 1 rbpeters rbpeters 0 Jun 7 21:25 really_big.log

5 1 1

4096 41 12288

14:08 10:08 10:08

This constructor expects the client to ensure that the memory for the key is not deallocated and the pointer to the key remains valid until the SampleCipher instance is destroyed. The constructor of the wrapper class does not meet both requirements. Since no tracking handle to the managed array is stored in the managed wrapper class, the GC could clean up the managed array before the native class is destroyed. Even if a tracking handle to the managed array ensures that the memory is not reclaimed, the array could be relocated during garbage collection. In this case, the native pointer would no longer refer to the managed array. To ensure that the key s memory is not reclaimed and that the key s data is not relocated during garbage collection, it should be copied on the native heap. This requires changes in the constructor as well as the destructor of the managed wrapper class. The following code shows how the constructor and the destructor could be implemented: public ref class SampleCipher { unsigned char* pKey; NativeLib::SampleCipher* pWrappedObject; public: SampleCipher(array<Byte>^ key) : pKey(0), pWrappedObject(0) { if (!key) throw gcnew ArgumentNullException("key"); pKey = new unsigned char[key->Length]; if (!pKey) throw gcnew OutOfMemoryException("Allocation on C++ free store failed"); try { Marshal::Copy(key, 0, IntPtr(pKey), key->Length); pWrappedObject = new NativeLib::SampleCipher(pKey, key->Length); if (!pWrappedObject) throw gcnew OutOfMemoryException("Allocation on C++ free store failed"); } catch (Object^) { delete[] pKey; throw; } } ~SampleCipher() { try { delete pWrappedObject;