LDicomDS::GetPrevElement

#include "Ltdic.h"

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

pDICOMELEMENT pElement;	/* pointer to a DICOMELEMENT structure */
L_BOOL bTree;	/* flag that indicates how to evaluate the Data Set */
L_BOOL bVolatile;	/* flag that indicates the type of element to retrieve */

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

Parameter	Description
pElement	Pointer to a DICOMELEMENTstructure 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.
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.
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

!NULL	A pointer to a DICOMELEMENTstructure 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. Please note that 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. Please note that 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:

LDicomDS::GetFirstElement

LDicomDS::GetLastElement

LDicomDS::GetNextElement

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

LDicomDS::GetRootElement

LDicomDS::GetParentElement

LDicomDS::GetChildElement

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

See Also

Functions:	LDicomDS::GetFirstElement, LDicomDS::GetPrevElement, LDicomDS::GetNextElement, LDicomDS::GetCountModule, LDicomDS::GetRootElement, LDicomDS::GetParentElement, LDicomDS::GetChildElement, LDicomDS::IsVolatileElement
Topics:	Working with Data Sets
	How to Disable the Automatic Loading of the default DICOM IOD Table

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;
}