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Compress the contents of the specified file.
Syntax
object.CompressFile( InputFile,
OutputFile, [CompressionType],
[CompressionLevel] )
Parameters
- InputFile
- A string value that is the name of the file that will be compressed. The file must
exist, and it must be a regular file that can be opened for reading
by the current process. An error will be returned if a character
device, such as the console, is specified as the file name.
- OutputFile
- A string value that is the name of the file that is to contain the compressed 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 will be
used to compress the data. One of the following values may be
specified. If this argument is not specified, the Deflate algorithm
is used.
| 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 and provides a
good balance between the data compression ratio and system
resources used. This is the default compression method. |
| 2 |
fileCompressionBzip2 |
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. |
| 3 |
fileCompressionLzma |
A compression algorithm that combines the LZ77 algorithm
for dictionary-based compression with range encoding to
efficiently represent repetitive patterns in the data. LZMA
can achieve higher compression ratios than Deflate or the
Burrows-Wheeler algorithms; however, it requires more memory
and CPU resources due to the larger dictionary sizes and more
complex encoding algorithm. |
- CompressionLevel
- A numeric value which specifies the compression level to use. A
value of zero specifies that the default compression level
appropriate for the selected algorithm should be used, balancing
resource usage and the compression ratio of the data. A value of 1
specifies that the compression should be performed using minimal
memory resources, at the expense of the compression ratio. The
maximum value of 9 specifies that the algorithm should use more
memory to achieve the maximum compression ratio. It is recommended
that most applications use the default value of zero.
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.
Remarks
The CompressFile method compresses the contents of the
specified file. The compression ratio achieved depends on the type of
file being compressed. Note that the compressed file is not stored in
an archive format that is recognized by third-party applications such
as PKZip or WinZip.
If the output file already exists, it will be replaced with the
compressed contents of the input file. If the compression fails for
any reason, the output file will be deleted. If you want to
ensure an existing output file will be preserved if an error occurs,
you should create a temporary file and use it as the output file. If
this method succeeds, then you can rename or copy the temporary file
which contains the compressed data.
See Also
CompareFile Method,
CompressData Method,
DecodeFile Method,
EncodeFile Method,
ExpandFile Method
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