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Annotation of mstools/mfc/src/elements.h, revision 1.1.1.1

1.1       root        1: // This is a part of the Microsoft Foundation Classes C++ library. 
                      2: // Copyright (C) 1992 Microsoft Corporation 
                      3: // All rights reserved. 
                      4: //  
                      5: // This source code is only intended as a supplement to the 
                      6: // Microsoft Foundation Classes Reference and Microsoft 
                      7: // QuickHelp documentation provided with the library. 
                      8: // See these sources for detailed information regarding the 
                      9: // Microsoft Foundation Classes product. 
                     10: 
                     11: // Collection implementation helpers
                     12: 
                     13: /*
                     14: * The short story:
                     15: *   this file contains inline functions that make up the building blocks
                     16: *   for implementing the string versions of standard parameterized
                     17: *   collection shapes
                     18: *
                     19: * The long story:
                     20: *   Because the implementation of collection classes moves objects around
                     21: *   in various ways, it is very inefficient to use only generic C++ constructs.
                     22: *   For example, in order to grow an array of FOO objects by one element,
                     23: *   you would be forced to allocate a new array of appropriate size, calling
                     24: *   the FOO constructor on every element.  Then copy the original array, element
                     25: *   by element using a possibly overloaded assignment operator.  Finally destroy
                     26: *   the original array element by element.
                     27: *   For built-in data types (WORD, DWORD, pointer types), this is complete
                     28: *   overkill.  For non-trivial classes (eg: CString in particular) this is
                     29: *   a terrible implementation.
                     30: *   
                     31: *   The bottom line: we have to have special routines for doing construction
                     32: *   and destruction of arrays of special elements - in particular CStrings.
                     33: *   The standard templates are parameterized on 'HAS_CREATE' which is
                     34: *   non-zero if the collection implementation requires a special
                     35: *   construct and destruct function.
                     36: * 
                     37: *   Please note that these are inline overloaded operators, and do not have
                     38: *   any form of runtime polymorphism (i.e. nothing is 'virtual').
                     39: */
                     40: 
                     41: /////////////////////////////////////////////////////////////////////////////
                     42: // Special implementations for CStrings
                     43: // it is faster to bit-wise copy a CString than to call an official
                     44: //   constructor - since an empty CString can be bit-wise copied
                     45: 
                     46: extern const CString NEAR afxEmptyString;
                     47: 
                     48: static inline void ConstructElement(CString* pNewData)
                     49: {
                     50:        memcpy(pNewData, &afxEmptyString, sizeof(CString));
                     51: }
                     52: 
                     53: static inline void DestructElement(CString* pOldData)
                     54: {
                     55:        pOldData->Empty();
                     56: }
                     57: 
                     58: /////////////////////////////////////////////////////////////////////////////

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