---
product: Chilkat
product_version: 11.7.0
language: xojo
language_label: Xojo
class: ZipCrc
license: bundle
deprecated: false
reference_html: https://www.chilkatsoft.com/refdoc/xojoZipCrcRef.html
---
# Chilkat ZipCrc — Xojo — v11.7.0

> Chilkat 11.7.0 · language=xojo · class=ZipCrc
> Other versions: replace `11.7.0` in this URL. Other languages: `https://www.chilkatsoft.com/ai-docs/v/11.7.0/<lang>/classes/ZipCrc.md`.
> Language-wide rules (install, unlock, error model, strings/bytes): `https://www.chilkatsoft.com/ai-docs/v/11.7.0/xojo/guide.md`.

## Purpose

**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**

Use `CalculateCrc` to calculate a ZIP-style CRC32 value for an in-memory byte array.

**BinData support**

Use `CrcBd` when the input bytes are already stored in a `Chilkat.BinData` object.

**String CRCs**

Use `CrcString` or `CrcSb` to calculate CRC32 for text using a specific charset such as `utf-8`, `utf-16`, or `windows-1252`.

**File CRCs**

Use `FileCrc` to calculate the CRC32 of a file while streaming the file contents to keep memory usage small and constant.

**Streaming calculation**

Call `BeginStream`, add chunks with `MoreData`, and finish with `EndStream` when data arrives incrementally.

**Hex formatting**

Use `ToHex` to convert a 32-bit CRC integer into a readable hexadecimal string.

**Common pattern:** Use `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.

**ZIP compatibility note:** The CRC returned by this class is the same 32-bit CRC value that would appear in a ZIP file header for the same byte content. When calculating CRCs for strings, the selected charset matters because the CRC is computed over bytes, not abstract characters.

## Object creation, unlocking and error handling

**Object Creation**

```xojo
Dim zipCrc As New Chilkat.ZipCrc
```

Call `Global.UnlockBundle` once at the start of the program, before using this or any other Chilkat class. Any string unlocks a fully functional 30-day trial; a purchased unlock code is used in production. See `guide.md` for the exact code in Xojo.

How failure is reported depends on the method's return type and is stated in the note under each method below. In every case the diagnostic text is in the `LastErrorText` property of the object whose method was called.

## Members common to every Chilkat class

Documented once per language in `common-members.md`; listed here so this page is self-contained.

| Property | Signature | Access | Meaning |
|---|---|---|---|
| `DebugLogFilePath` | `DebugLogFilePath As String` | read/write | If set to a file path, this property logs the LastErrorText of each Chilkat method or property call to the specified file. |
| `LastErrorHtml` | `LastErrorHtml As String (read-only)` | read-only | Provides HTML-formatted information about the last called method or property. |
| `LastErrorText` | `LastErrorText As String (read-only)` | read-only | Provides plain text information about the last called method or property. |
| `LastErrorXml` | `LastErrorXml As String (read-only)` | read-only | Provides XML-formatted information about the last called method or property. |
| `LastMethodSuccess` | `LastMethodSuccess As Boolean` | read/write | Indicates the success or failure of the most recent method call: `True` means success, `False` means failure. |
| `VerboseLogging` | `VerboseLogging As Boolean` | read/write | If set to `True`, then the contents of LastErrorText (or LastErrorXml, or LastErrorHtml) may contain more verbose information. |
| `Version` | `Version As String (read-only)` | read-only | Version of the component/library, such as "10.1.0" |

## Member index

| Member | Kind | Signature |
|---|---|---|
| `BeginStream` | method | `Sub BeginStream()` |
| `CalculateCrc` | method | `Function CalculateCrc(data As MemoryBlock) As UInt32` |
| `CrcBd` | method | `Function CrcBd(bd As Chilkat.BinData) As UInt32` |
| `CrcSb` | method | `Function CrcSb(sb As Chilkat.StringBuilder, charset As String) As UInt32` |
| `CrcString` | method | `Function CrcString(str As String, charset As String) As UInt32` |
| `EndStream` | method | `Function EndStream() As UInt32` |
| `FileCrc` | method | `Function FileCrc(path As String) As UInt32` |
| `LoadTaskCaller` | method | `Function LoadTaskCaller(task As Chilkat.Task) As Boolean` |
| `MoreData` | method | `Sub MoreData(data As MemoryBlock)` |
| `ToHex` | method | `Function ToHex(crc As UInt32) As String` |

## Methods

### ZipCrc.BeginStream

`Chilkat 11.7.0 · xojo · ZipCrc · BeginStream · method`

```xojo
Sub 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.

### ZipCrc.CalculateCrc

`Chilkat 11.7.0 · xojo · ZipCrc · CalculateCrc · method`

```xojo
Function CalculateCrc(data As MemoryBlock) As UInt32
```

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.

### ZipCrc.CrcBd

`Chilkat 11.7.0 · xojo · ZipCrc · CrcBd · method · since 9.5.0.75`

```xojo
Function CrcBd(bd As Chilkat.BinData) As UInt32
```

Calculates a CRC32 for the bytes contained in `bd`.

### ZipCrc.CrcSb

`Chilkat 11.7.0 · xojo · ZipCrc · CrcSb · method · since 9.5.0.75`

```xojo
Function CrcSb(sb As Chilkat.StringBuilder, charset As String) As UInt32
```

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.

### ZipCrc.CrcString

`Chilkat 11.7.0 · xojo · ZipCrc · CrcString · method · since 9.5.0.75`

```xojo
Function CrcString(str As String, charset As String) As UInt32
```

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.

### ZipCrc.EndStream

`Chilkat 11.7.0 · xojo · ZipCrc · EndStream · method`

```xojo
Function EndStream() As UInt32
```

Finalizes and returns the Zip CRC value calculated by calling BeginStream followed by multiple calls to MoreData.

### ZipCrc.FileCrc

`Chilkat 11.7.0 · xojo · ZipCrc · FileCrc · method`

```xojo
Function FileCrc(path As String) As UInt32
```

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.

Async variant: `FileCrcAsync` — same arguments, returns a `Task` (see Async variants below).

### ZipCrc.LoadTaskCaller

`Chilkat 11.7.0 · xojo · ZipCrc · LoadTaskCaller · method · since 9.5.0.80`

```xojo
Function LoadTaskCaller(task As Chilkat.Task) As Boolean
```

Loads the caller of the task's async method.

Returns True for success, False for failure.

### ZipCrc.MoreData

`Chilkat 11.7.0 · xojo · ZipCrc · MoreData · method`

```xojo
Sub MoreData(data As MemoryBlock)
```

Adds additional data to the CRC currently being calculated. (See BeginStream for more information.)

### ZipCrc.ToHex

`Chilkat 11.7.0 · xojo · ZipCrc · ToHex · method`

```xojo
Function ToHex(crc As UInt32) As String
```

Converts a 32-bit integer to a hex string.

Returns `Nil` on failure

## Events and callbacks

In Xojo, Chilkat events are handled by subclassing. Add a new class to your project that inherits from Chilkat.ZipCrc, then override the event methods you want to respond to. Any method you don't override keeps its default do-nothing behavior, so you only need to write the ones you actually care about.

From that point on, create and use an instance of your subclass wherever you would have used a Chilkat.ZipCrc. The events fire on your instance automatically as the object does its work.

**For example:**

```vb
class MyZipCrc
    Inherits Chilkat.ZipCrc

    Function AbortCheck() As Boolean
    Function PercentDone(pctDone As Int32) As Boolean
    Sub ProgressInfo(name As String, value As String)
    Sub TaskCompleted(task As Chilkat.Task)

End Class
```

### ZipCrc.AbortCheck (event)

`Chilkat 11.7.0 · xojo · ZipCrc · AbortCheck · event`

```xojo
Function AbortCheck() As Boolean
```

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.

### ZipCrc.PercentDone (event)

`Chilkat 11.7.0 · xojo · ZipCrc · PercentDone · event`

```xojo
Function PercentDone(pctDone As Int32) As Boolean
```

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.

### ZipCrc.ProgressInfo (event)

`Chilkat 11.7.0 · xojo · ZipCrc · ProgressInfo · event`

```xojo
Sub ProgressInfo(name As String, value As String)
```

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.

### ZipCrc.TaskCompleted (event)

`Chilkat 11.7.0 · xojo · ZipCrc · TaskCompleted · event`

```xojo
Sub TaskCompleted(task As Chilkat.Task)
```

Called from the background thread when an asynchronous task completes.

## Async variants

Each returns a `Task` instead of the result and takes the same arguments as the synchronous method; run the task, wait for `Finished`, then read the result from the task. No new Async methods are added from 11.7.0 on.

```xojo
Function FileCrcAsync(path As String) As Chilkat.Task
```

## Related classes

[`BinData`](https://www.chilkatsoft.com/ai-docs/v/11.7.0/xojo/classes/BinData.md), [`StringBuilder`](https://www.chilkatsoft.com/ai-docs/v/11.7.0/xojo/classes/StringBuilder.md), [`Task`](https://www.chilkatsoft.com/ai-docs/v/11.7.0/xojo/classes/Task.md)