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LDicomDS::GetPrevElement

Summary

Returns a pointer to the item in the Data Set that immediately precedes the specified item.

Syntax

#include "Ltdic.h"

pDICOMELEMENT LDicomDS::GetPrevElement(pElement, bTree, bVolatile)

Parameters

pDICOMELEMENT pElement

Pointer to a DICOMELEMENT structure that contains an item in the Data Set. A pointer to the item in the Data Set that immediately precedes this item will be returned.

L_BOOL bTree

Flag that indicates how the Data Set will be evaluated. Possible values are:

Value	Meaning
TRUE	Evaluate the Data Set as a tree.
FALSE	Evaluate the Data Set as a list.

L_BOOL bVolatile

Flag that indicates the type of element to retrieve. Possible values are:

Value	Meaning
TRUE	Retrieve any previous element, volatile or non-volatile.
FALSE	Retrieve a non-volatile previous element.

Returns

Value	Meaning
!NULL	A pointer to a DICOMELEMENT structure that contains the item in the Data Set that immediately precedes the item specified in pElement.
NULL	There is not an item preceding pElement. (pElement is the first item in the Data Set.)

Comments

If the Data Set is evaluated as a tree structure, this function returns the previous item on the same level as pElement with the same parent as pElement.

NOTE: The numbering of the items in this illustration is arbitrary and does not imply order.

$image\GetPvTr.gif$

If the passed pointer points to	The function returns a pointer to
Item 1	Item 2
Item 3	Item 4
Item 5	NULL
Item 6	Item 7

If the Data Set is evaluated as a list, the previous item in the list is returned.

NOTE: The numbering of the items in this illustration does indicate the order of the items when the Data Set is evaluated as a list.

$image\GetPvLst.gif$

If the passed pointer points to	The function returns a pointer to
Item 1	NULL
Item 15	Item 14
Item 5	Item 4
Item 9	Item 8
Item 22	Item 21
Item 25	Item 24

The following functions will also help you navigate the Data Set as either a tree or a list:

If you evaluate the Data Set as a tree, you can also use the following functions to navigate the tree:

A volatile element is an element that can be changed or destroyed in the process of inserting or setting an image. A non-volatile element is an element that must be changed manually. It is not changed or destroyed by inserting or setting an image.

For example, a grayscale image has elements TAG_SMALLEST_IMAGE_PIXEL_VALUE, TAG_LARGEST_IMAGE_PIXEL_VALUE, etc. If the image is changed to a color image, these elements disappear and the following elements appear: TAG_RED_PALETTE_COLOR_LOOKUP_TABLE_DESCRIPTOR, etc. These are volatile elements since they are changed or destroyed when an image is changed or set.

To retrieve a previous element that must be changed manually, i.e. is not volatile, set bVolatile to FALSE. To retrieve either volatile or non-volatile previous element, set bVolatile to TRUE.

Required DLLs and Libraries

LTDIC
For a listing of the exact DLLs and Libraries needed, based on the toolkit version, refer to Files To Be Included With Your Application

Platforms

Win32, x64

Example

This example displays in a list-box control all elements (level 0) from the Data Set.

L_INT LDicomDS_GetPrevElementExample(CListBox *pDlg) 
{ 
   LDicomDS*      pDS; 
   pDICOMELEMENT  pElement; 
   pDICOMTAG      pTag; 
   L_TCHAR        szUnknown[]=TEXT("Unknown"); 
   L_TCHAR*       p; 
 
   pDS = new LDicomDS(NULL); 
 
   pDS->InitDS( CLASS_XA_BIPLANE_IMAGE_STORAGE_RETIRED, 0);  
 
   pElement = pDS->GetLastElement(NULL, TRUE, FALSE); 
   while (pElement != NULL) 
   { 
      pTag = LDicomTag::Find(pElement->nTag); 
      if (pTag != NULL) 
      { 
         p = pTag->pszName; 
      } 
      else 
      { 
         p = szUnknown; 
      } 
 
      pDlg->AddString(p); 
 
      pElement = pDS->GetPrevElement(pElement, TRUE, FALSE); 
   } 
 
   delete pDS; 
 
   return DICOM_SUCCESS; 
}