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Expands the contents of a previously specified file.
Syntax
object.ExpandFile( InputFile,
OutputFile, [CompressionType] )
Remarks
The ExpandFile method expands the contents of a
previously compressed file. The following parameters should be
passed as arguments to the method:
- InputFile
- The name of the file that is to be expanded. The file must
exist, and it must be a file that was created by a previous call to
the CompressFile method. An error will be returned if the
file cannot be accessed, if it specifies a character device such as
the console, or the if the data is not in a recognizable
format.
- OutputFile
- The name of the file that is to contain the expanded file data.
If the file exists, it must be a regular file that can be opened
for writing by the current process and will be overwritten. If the
file does not exist, it will be created. An error will be returned
if a character device, such as the console, is specified as the
file name.
- CompressionType
- A numeric value which determines the algorithm that was used to
compress the data. One of the following values may be specified. If
this argument is not specified, the Deflate algorithm is used. If
the compression type specified by this argument does not match the
actual compression algorithm used to compress the file, an error
will be returned.
| Value |
Constant |
Description |
| 1 |
fileCompressionDeflate |
A compression algorithm that combines LZ77
algorithm for creating common substrings and Huffman coding to
process the different frequencies of byte sequences in the data
stream. Deflate is widely used by compression software. |
| 2 |
fileCompressionBurrowsWheeler |
A compression algorithm that rearranges blocks
of data in sorted order and then uses Huffman coding to process
different frequencies of data within the block. Burrows-Wheeler
compression provides a better compression ratio than the Deflate
algorithm, however it requires more resources to perform the
compression. |
Note that it is permitted to specify an empty string as the
output file name. In this case, the control will create a temporary
file in the directory specified by the TEMP environment variable.
After the file has been expanded, the OutputFile property
will be set the name of the temporary file that has been created.
It is the responsibility of the application to delete this
temporary file after it is no longer needed.
Note that this method can only expand files that were compressed
using the control. It cannot expand the contents of a file stored
in an archive format such as PKZip or WinZip.
Return Value
This method returns a value of zero if the file was successfully
compressed. A non-zero return value specifies an error code which
indicates the reason for the failure.
See Also
CompressFile Method, DecodeFile Method, EncodeFile Method
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