ZipCrc FoxPro 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.
Object Creation
loZipCrc = CreateObject('Chilkat.ZipCrc')Visual FoxPro is a 32-bit application and therefore uses the 32-bit Chilkat ActiveX. To bind to a specific major version of Chilkat, append the major version number to the ProgID, such as CreateObject('Chilkat.ZipCrc.11') for Chilkat v11.*.*.
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.
LastBinaryResult
This property is mainly used in SQL Server stored procedures to retrieve binary data from the last method call that returned binary data. It is only accessible if Chilkat.Global.KeepBinaryResult is set to 1. This feature allows for the retrieval of large varbinary results in an SQL Server environment, which has restrictions on returning large data via method calls, though temp tables can handle binary properties.
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: 1 means success, 0 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.
LastStringResult
In SQL Server stored procedures, this property holds the string return value of the most recent method call that returns a string. It is accessible only when Chilkat.Global.KeepStringResult is set to TRUE. SQL Server has limitations on string lengths returned from methods and properties, but temp tables can be used to access large strings.
LastStringResultLen
The length, in characters, of the string contained in the LastStringResult property.
topVerboseLogging
If set to 1, then the contents of LastErrorText (or LastErrorXml, or LastErrorHtml) may contain more verbose information. The default value is 0. 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.
topCalculateCrc
Calculates a 32-bit CRC for in-memory byte data. This is the 32-bit CRC that would be found in a Zip file header if a file containing the data was added to a zip archive. Returns the CRC32 of the data.
CrcBd
Calculates a CRC32 for the bytes contained in bd.
CrcSb
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
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.
FileCrcAsync (1)
Creates an asynchronous task to call the FileCrc method with the arguments provided.
Note: Async method event callbacks happen in the background thread. Accessing and updating UI elements existing in the main thread may require special considerations.
Returns .NULL. on failure
LoadTaskCaller
MoreData
Adds additional data to the CRC currently being calculated. (See BeginStream for more information.)
topToHex
Events
A Visual FoxPro application receives Chilkat ActiveX events by defining a class that IMPLEMENTS the _IChilkatEvents interface, creating an instance of it, and binding that instance to the Chilkat object with EVENTHANDLER(). Visual FoxPro requires the class to implement every method of the interface, so the class below includes a PROCEDURE for each event; leave the ones you do not need empty. The TextData and BinaryData events are defunct: they are deprecated and are never called, but their procedures must still exist because the interface declares them.
Important: Event callbacks from asynchronous method calls are generally not possible from the ActiveX. Events fire during synchronous method calls.
zipCrcEventHandler = CREATEOBJECT("MyZipCrcEvents")
loZipCrc = CreateObject('Chilkat.ZipCrc')
EVENTHANDLER(loZipCrc, zipCrcEventHandler)
DEFINE CLASS MyZipCrcEvents AS SESSION OLEPUBLIC
IMPLEMENTS _IChilkatEvents IN "Chilkat.ZipCrc"
PROCEDURE _IChilkatEvents_AbortCheck(abort As Number)
? "AbortCheck"
ENDPROC
* The BinaryData event is defunct: it is deprecated and is never called.
* The procedure must exist because the interface declares it, but it can be left empty.
PROCEDURE _IChilkatEvents_BinaryData(data As Variant)
ENDPROC
PROCEDURE _IChilkatEvents_PercentDone(pctDone As Number, abort As Number)
? "PercentDone"
ENDPROC
PROCEDURE _IChilkatEvents_ProgressInfo(name As String, value As String)
? "ProgressInfo"
ENDPROC
PROCEDURE _IChilkatEvents_TaskCompleted(task As Generic)
? "TaskCompleted"
ENDPROC
* The TextData event is defunct: it is deprecated and is never called.
* The procedure must exist because the interface declares it, but it can be left empty.
PROCEDURE _IChilkatEvents_TextData(data As String)
ENDPROC
ENDDEFINE
AbortCheck
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.
FoxPro event implementation:
* Add to the MyZipCrcEvents class shown in the Events overview above.
PROCEDURE _IChilkatEvents_AbortCheck(abort As Number)
* Set abort to 1 to abort the method in progress.
ENDPROC
PercentDone
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 1. This will cause the method to terminate and return a failure status or corresponding failure value.
FoxPro event implementation:
* Add to the MyZipCrcEvents class shown in the Events overview above.
PROCEDURE _IChilkatEvents_PercentDone(pctDone As Number, abort As Number)
* pctDone ranges from 1 to 100. Set abort to 1 to abort the method in progress.
ENDPROC
ProgressInfo
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.
FoxPro event implementation:
* Add to the MyZipCrcEvents class shown in the Events overview above.
PROCEDURE _IChilkatEvents_ProgressInfo(name As String, value As String)
? name + ": " + value
ENDPROC
TaskCompleted
Called from the background thread when an asynchronous task completes.
FoxPro event implementation:
* Add to the MyZipCrcEvents class shown in the Events overview above.
PROCEDURE _IChilkatEvents_TaskCompleted(task As Generic)
* task is the Task object that has completed.
ENDPROC