classwork.pp

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Class AStreamBookmark

DescriptionHierarchyFieldsMethodsProperties

Unit

classwork

Declaration

type AStreamBookmark = class(AStringLeaf)

Description

This class represents a stream bookmark, which is a way of associating a name with a specific location in a stream. This is useful in cases where you want to open an arbitrary stream and find the position of a specific piece of data, but you don't know ahead of time where that data will be in the stream.

Stream bookmarks are managed by instances of AStreamBookmarkDictionary, which provides a way to look up a specific bookmark and which can also read and write a list of bookmarks to a given stream.

Hierarchy

Overview

Fields

Protected myBookmarkType: TStreamBookmarkType;
Protected myPosition: TStreamOffset;

Methods

Public constructor named(const thisKey: string; const thisPosition: TStreamOffset); reintroduce; virtual;
Public constructor atCurrentPositionIn(const Source: AStream; const thisName: string); virtual;
Public function init: boolean; override;
Public function selfStreamingLength: TStreamIOSize; override;
Public function writeSelfTo(const Dest: AStream): TStreamIOSize; override;
Public function readFrom(const Source: AStream): TStreamIOSize; override;
Public function toString: AnsiString; override;
Public function bookmarkType: TStreamBookmarkType; virtual;
Public function position: TStreamOffset; virtual;
Public function setPosition(const newPosition: TStreamOffset): TStreamOffset; virtual;
Public function setToCurrentPositionIn(const Source: AStream): TStreamOffset; virtual;

Description

Fields

Protected myBookmarkType: TStreamBookmarkType;

Indicates the type of bookmark represented

Protected myPosition: TStreamOffset;

Stores the position in the stream where the data referenced by the bookmark may be found.

Methods

Public constructor named(const thisKey: string; const thisPosition: TStreamOffset); reintroduce; virtual;

Construct a new bookmark with the given name and given stream position.

Public constructor atCurrentPositionIn(const Source: AStream; const thisName: string); virtual;

Construct a new bookmark with the given name, using the current position within the specified stream.

If Source is valid (not Nil), this method will call AStream.position on it and use the value returned as the position to which the bookmark refers.

Public function init: boolean; override;

Initializer

Public function selfStreamingLength: TStreamIOSize; override;

Calculate the number of bytes required to stream the bookmark.

This method builds upon the behavior inherited from AStringLeaf.selfStreamingLength: it calls the inherited routine, then adds the number of bytes required to store the bookmark type and position reference.

Public function writeSelfTo(const Dest: AStream): TStreamIOSize; override;

Write the bookmark, and just the bookmark, to the given stream.

This method builds upon the behavior inherited from AStringLeaf.writeSelfTo; it first calls the inherited routine, then writes the value of AStreamBookmark.position.

Returns

The total number of bytes written to Dest.

Public function readFrom(const Source: AStream): TStreamIOSize; override;

Read the bookmark from the given stream.

This method builds upon the behavior inherited from AStringLeaf.readFrom; it first calls the inherited routine, then reads the value of AStreamBookmark.position.

Returns

The total number of bytes read from Source.

Public function toString: AnsiString; override;

Construct a string representation of the bookmark, suitable for output to a text-based device, such as a console.

This method overrides the behavior inherited from AStringLeaf.toString. It returns a string that is constructed based on the format specified by stbmStringRepresentation. In the default implementation, this string will contain the name of the bookmark as well as the position in the stream to which it refers.

Public function bookmarkType: TStreamBookmarkType; virtual;

Retrieve the type of bookmark represented by the instance.

This value is used when reading bookmarks from a stream to ensure the correct instance of AStreamBookmark or its descendants is created.

Public function position: TStreamOffset; virtual;

Retrieve the position in the stream to which the bookmark refers.

Public function setPosition(const newPosition: TStreamOffset): TStreamOffset; virtual;

Set the position in the stream to which the bookmark refers.

thisPosition must be a positive value which specifies the offset, in bytes, from the beginning of the stream to which the bookmark refers. The beginning of the stream is always at offset zero (0). If thisPosition is negative, this routine will do nothing.

Returns

The previous value of AStreamBookmark.position.

Public function setToCurrentPositionIn(const Source: AStream): TStreamOffset; virtual;

Set the position in the stream to which the bookmark refers by querying the specified stream.

If Source is valid (not Nil), then this method calls AStream.position on it and stores the result.

Returns

The previous value of AStreamBookmark.position.

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