Current issue

Vol.26 No.4

Vol.26 No.4


© 1984-2017
British APL Association
All rights reserved.

Archive articles posted online on request: ask the archivist.


Volume 23, No.1

Basic guide to using
Windows XP file compression facilities
from APL+Win

Ajay Askoolum

Verify file

Verify whether a file exists using PathFileExists; this is an API call. If this declaration is not found in your INI file, add it, thus:

⎕wcall 'W_Ini' '[Call]PathFileExists=L(*C pszPath) ALIAS PathFileExistsA LIB shlwapi.dll'

The test to verify declaration is:

      ⍴⎕wcall 'W_Ini' '[Call]PathFileExists' ⍝ 0 = Missing

Create empty Zip file

An empty Zip file can be created using the following function:

    ∇ Z←CreateZipFile R
[1]   ⍝ Ajay Askoolum
[2]   :if 0=⎕wcall 'PathFileExists' R
[3]      R ⎕xncreate Z←¯1+⌊/0,⎕nnums,⎕xnnums
[4]      ('PK¨←',(18⍴⎕tcnul),⎕tcnl,⎕tclf) ⎕nappend Z
[5]      ⎕nuntie Z
[6]      Z←1
[7]   :else
[8]      Z←0
[9]   :endif

This function returns 1 if successful and 0 otherwise; the right-hand argument is a fully qualified filename.

      CreateZipFile 'c:\'

Signature of Zip file

The first 22 bytes of the file varies, depending on the application that created the Zip file. A file created thus can be used by WinZip. You can write a function to verify whether a particular file is a ZIP file by matching the first 4 bytes—see line [4].

Add files to an existing Zip file

The following function will add a list of files to an existing Zip file:

    ∇ Z←L AddToZip R;⎕wself
[1]   ⍝ Ajay Askoolum
[2]   ⍝ L = Fully qualified name of an existing and valid Zip file
[3]   ⍝ R is a list of files to add or refresh inside ZIP
[4]   :if 0=⍴'ShApp' ⎕wi 'self'
[5]      ⎕wself←'ShApp' ⎕wi 'Create' 'Shell.Application'
[6]   :else
[7]      ⎕wself←'ShApp'
[8]   :endif
[9]   :while 0≠⍴R←,R
[10]     ⎕wi 'xNamespace().CopyHere' L (⎕io⊃R)
[11]     R←1↓R
[12]  :endwhile

Note that the function does not delete the instance of the Shell Application object; this is deliberate and intended to save time creating the object when the function is used repeatedly.

      ⍝ Add a single file
'c:\' AddToZip ⊂'c:\Comparing the Excel COM Interface.doc'
      ⍝ Add multiple files
'c:\' AddToZip files

Using Winzip to explore

The file can be opened by WinZip; see below.

Opening with WinZip

List file names within Zip file

The list of files in a given Zip file can be returned by this function:

    ∇ Z←L EnumZip R;⎕wself;i;j
[1]   ⍝ Ajay Askoolum
[2]   ⍝ Return list of files found in Zip file R
[3]   :if 0=⍴'ShApp' ⎕wi 'Self'
[4]      ⎕wself←'ShApp' ⎕wi 'Create' 'Shell.Application'
[5]   :else
[6]      ⎕wself←'ShApp'
[7]   :endif
[8]   Z←0/⊂''
[9]   :if 0≠⎕wi 'xNamespace()' R ⍝ Verify existence
[10]     ⎕wi 'xNamespace().Items>.tr' R
[11]     :if 0≠i←'.tr' ⎕wi 'xCount'
[12]        i←(-⎕io)+⍳i
[13]        j←(⊂'.tr') ⎕wi¨ (⊂⊂'xItem().Path'),¨i ⍝ Contents
[14]        L←(⊂'.tr') ⎕wi¨ (⊂⊂'xItem().IsFolder'),¨i
[15]        Z←Z,(~L)/j                            ⍝ Files
[16]        :if 0≠⍴L←L/j                          ⍝ Folders
[17]           R←(1≥+\'\'=R)/R
[18]           Z←Z,⊃,/EnumZip ¨(⊂R,'\'),¨L
[19]        :endif
[20]     :endif
[21]  :endif
[22]  :if 1=+/'EnumZip'^.⍉⎕si[;⍳7]
[23]     :if 0≠⍴'.tr' ⎕wi 'self'
[24]        '.tr' ⎕wi 'Delete'
[25]     :endif
[26]  :endif

Note that this is a recursive function.

      EnumZip 'c:\'
Comparing the Excel COM Interface.doc DSC00001.JPG SHELL.w3
      ⍴EnumZip 'c:\'
      ⊃EnumZip 'c:\'
Comparing the Excel COM Interface.doc

Extracting files from Zip file

The following function will extract the files from an existing Zip file into a specified location:

    ∇ L ExtractZip R;⎕wself
[1]   ⍝ Ajay Askoolum
[2]   ⍝ L is the target location for extracted files
[3]   ⍝ R is the fully qualified name of Zip file
[4]   :if 0=⍴'ShApp' ⎕wi 'self'
[5]      ⎕wself←'ShApp' ⎕wi 'Create' 'Shell.Application'
[6]   :else
[7]      ⎕wself←'ShApp'
[8]   :endif
[9]      ⎕wi 'NameSpace().CopyHere' L ((⎕wi 'NameSpace().Items' R) ⎕wi 'obj')
      'c:\zzz' ExtractZip 'c:\'
      ⎕lib 'c:\zzz'
Comparing the Excel COM Interface.doc

Note that the target location must exist.

What is missing?

Lots! If you examine the properties, methods, and events of the Shell object, it is clear that this object does not expose the compression properties or methods.


It is possible to do lots more with these facilities; I’ll leave you to explore.

Valid HTML 4.01 Strict

script began 8:12:05
caching off
debug mode off
cache time 3600 sec
indmtime not found in cache
cached index is fresh
recompiling index.xml
index compiled in 0.2581 secs
read index
read issues/index.xml
identified 26 volumes, 101 issues
array (
  'id' => '10011600',
regenerated static HTML
article source is 'HTML'
source file encoding is 'UTF-8'
URL: =>
URL: askzip/image1.png => trad/v231/askzip/image1.png
URL: =>
URL: =>
completed in 0.2845 secs