ZipCrc Lazarus Pascal Reference Documentation
ZipCrc
Current Version: 11.6.0
Chilkat.ZipCrc
Use
Use
Use
Use
Call
Use Calculate ZIP-compatible CRC32 values for files, bytes, strings, and streamed data.
Chilkat.ZipCrc calculates the 32-bit CRC value used in ZIP file
headers. It can compute CRC32 values for in-memory byte arrays,
BinData, StringBuilder content, strings using a
specified character encoding, and entire files. It also supports streaming
CRC calculation, allowing applications to process large or incremental data
in chunks without holding the full input in memory.
CRC32 for byte data
CalculateCrc to calculate a ZIP-style CRC32 value for
an in-memory byte array.
BinData support
CrcBd when the input bytes are already stored in a
Chilkat.BinData object.
String CRCs
CrcString or CrcSb to calculate CRC32 for
text using a specific charset such as utf-8,
utf-16, or windows-1252.
File CRCs
FileCrc to calculate the CRC32 of a file while streaming
the file contents to keep memory usage small and constant.
Streaming calculation
BeginStream, add chunks with MoreData, and
finish with EndStream when data arrives incrementally.
Hex formatting
ToHex to convert a 32-bit CRC integer into a readable
hexadecimal string.
FileCrc for files, CalculateCrc or
CrcBd for binary data already in memory, and
CrcString or CrcSb for text where the byte
representation depends on a charset. For large or chunked input, initialize
the CRC with BeginStream, feed each block with
MoreData, and call EndStream to obtain the final
CRC32 value.
Create / Free
uses
Chilkat.ZipCrc;
var
obj: TZipCrc;
begin
obj := TZipCrc.Create;
try
if not obj.IsValid then
raise Exception.Create('Failed to create a TZipCrc instance.');
// ... use obj ...
finally
obj.Free;
end;
end;
Allocates the underlying CkZipCrc object and returns a new TZipCrc instance. Simply adding Chilkat.ZipCrc to the unit's uses clause is enough to locate and bind to the Chilkat shared library (DLL / .so / .dylib) at runtime — no separate load step is required. Check obj.IsValid after calling Create; it is False if the underlying library could not be found/loaded or the object could not be allocated (for example, when unlicensed).
Every TZipCrc created by calling Create should eventually be released by calling .Free (inherited from TObject). The destructor automatically disposes the underlying CkZipCrc handle. A native (unmanaged) memory leak occurs if the object is never freed.
Properties
DebugLogFilePath
If set to a file path, this property logs the LastErrorText of each Chilkat method or property call to the specified file. This logging helps identify the context and history of Chilkat calls leading up to any crash or hang, aiding in debugging.
Enabling the VerboseLogging property provides more detailed information. This property is mainly used for debugging rare instances where a Chilkat method call causes a hang or crash, which should generally not happen.
Possible causes of hangs include:
- A timeout property set to 0, indicating an infinite timeout.
- A hang occurring within an event callback in the application code.
- An internal bug in the Chilkat code causing the hang.
LastErrorHtml
Provides HTML-formatted information about the last called method or property. If a method call fails or behaves unexpectedly, check this property for details. Note that information is available regardless of the method call's success.
topLastErrorText
Provides plain text information about the last called method or property. If a method call fails or behaves unexpectedly, check this property for details. Note that information is available regardless of the method call's success.
LastErrorXml
Provides XML-formatted information about the last called method or property. If a method call fails or behaves unexpectedly, check this property for details. Note that information is available regardless of the method call's success.
topLastMethodSuccess
Indicates the success or failure of the most recent method call: True means success, False means failure. This property remains unchanged by property setters or getters. This method is present to address challenges in checking for null or Nothing returns in certain programming languages. Note: This property does not apply to methods that return integer values or to boolean-returning methods where the boolean does not indicate success or failure.
VerboseLogging
If set to True, then the contents of LastErrorText (or LastErrorXml, or LastErrorHtml) may contain more verbose information. The default value is False. Verbose logging should only be used for debugging. The potentially large quantity of logged information may adversely affect peformance.
Version
Methods
BeginStream
Provides a way to calculate a CRC by streaming the data a chunk at a time. An application would start by calling BeginStream. Then it would add data by calling MoreData for each additional chunk. After the last chunk has been processed, the EndStream method is called to return the CRC.
topCrcBd
function CrcBd(bd: TChilkatBase): LongWord;
Calculates a CRC32 for the bytes contained in bd.
CrcSb
function CrcSb(sb: TChilkatBase;
const charset: string): LongWord;
Calculates a CRC32 for the string contained in sb. The charset is the byte representation to be used for the sb when calculating the CRC32. It can be utf-8, utf-16, windows-1252, iso-8859-1, or any of the character encodings (charsets) listed at the link below.
CrcString
const charset: string): LongWord;
Calculates a CRC32 for a string. The charset is the byte representation to be used for the str when calculating the CRC32. It can be utf-8, utf-16, windows-1252, iso-8859-1, or any of the character encodings (charsets) listed at the link below.
EndStream
Finalizes and returns the Zip CRC value calculated by calling BeginStream followed by multiple calls to MoreData.
topFileCrc
Calculates the CRC32 of a file. The data contained in the file is streamed for the calculation to keep the memory footprint small and constant. Returns the CRC32 of the file.
LoadTaskCaller
function LoadTaskCaller(task: TChilkatBase): Boolean;
ToHex
Events
Chilkat for Pascal supports three synchronous event callbacks: OnAbortCheck, OnPercentDone, and OnProgressInfo. Each is a property of the class; assign a method of one of your own objects (an of object handler) to receive the callbacks, or assign nil to unhook. The handler types are declared in the Chilkat.Base unit:
TChilkatAbortCheckEvent = function(Sender: TChilkatBase): Boolean of object;
TChilkatPercentDoneEvent = function(Sender: TChilkatBase; PctDone: Integer): Boolean of object;
TChilkatProgressInfoEvent = procedure(Sender: TChilkatBase; const Name, Value: string) of object;All Chilkat methods are synchronous, so callbacks are invoked on the thread that called the method -- if the method was called from the main thread, it is safe to access UI elements from the handler. The HeartbeatMs property controls the frequency of OnAbortCheck callbacks (the default of 0 means no AbortCheck events fire). Returning True from an OnAbortCheck or OnPercentDone handler aborts the running method.
AbortCheck
property OnAbortCheck: TChilkatAbortCheckEvent;
Enables a method call to be aborted by triggering the AbortCheck event at intervals defined by the HeartbeatMs property. If HeartbeatMs is set to its default value of 0, no events will occur. For instance, set HeartbeatMs to 200 to trigger 5 AbortCheck events per second.
Event callback implementation:
// A handler is a method of one of your own classes, e.g. a form:
function TMyObject.ZipCrcAbortCheck(Sender: TChilkatBase): Boolean;
begin
// Called every HeartbeatMs milliseconds while a method is running.
// Return True to abort the method; return False to continue.
Result := False;
end;To add an event handler:
zipcrc := TZipCrc.Create;
zipcrc.HeartbeatMs := 250; // fire OnAbortCheck 4 times per second
zipcrc.OnAbortCheck := MyObject.ZipCrcAbortCheck;PercentDone
property OnPercentDone: TChilkatPercentDoneEvent;
This provides the percentage completion for any method involving network communications or time-consuming processing, assuming the progress can be measured as a percentage. This event is triggered only when it's possible and logical to express the operation's progress as a percentage. The pctDone argument will range from 1 to 100. For methods that finish quickly, the number of PercentDone callbacks may vary, but the final callback will have pctDone equal to 100. For longer operations, callbacks will not exceed one per percentage point (e.g., 1, 2, 3, ..., 98, 99, 100).
The PercentDone callback also acts as an AbortCheck event. For fast methods where PercentDone fires, an AbortCheck event may not trigger since the PercentDone callback already provides an opportunity to abort. For longer operations, where time between PercentDone callbacks is extended, AbortCheck callbacks enable more responsive operation termination.
To abort the operation, set the abort output argument to True. This will cause the method to terminate and return a failure status or corresponding failure value.
Event callback implementation:
// A handler is a method of one of your own classes, e.g. a form:
function TMyObject.ZipCrcPercentDone(Sender: TChilkatBase; PctDone: Integer): Boolean;
begin
// PctDone ranges from 1 to 100.
WriteLn('Percent done: ', PctDone);
// Return True to abort the method; return False to continue.
Result := False;
end;To add an event handler:
zipcrc := TZipCrc.Create;
zipcrc.OnPercentDone := MyObject.ZipCrcPercentDone;ProgressInfo
property OnProgressInfo: TChilkatProgressInfoEvent;
This event callback provides tag name/value pairs that detail what occurs during a method call. To discover existing tag names, create code to handle the event, emit the pairs, and review them. Most tag names are self-explanatory.
Note: Some Chilkat methods don't fire any ProgressInfo events.
Event callback implementation:
// A handler is a method of one of your own classes, e.g. a form:
procedure TMyObject.ZipCrcProgressInfo(Sender: TChilkatBase; const Name, Value: string);
begin
WriteLn(Name, ': ', Value);
end;To add an event handler:
zipcrc := TZipCrc.Create;
zipcrc.OnProgressInfo := MyObject.ZipCrcProgressInfo;