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7z ANSI-C Decoder 9.35
7z ANSI-C provides 7z/LZMA decoding.
7z ANSI-C version is simplified version ported from C++ code.
LZMA is default and general compression method of 7z format
in 7-Zip compression program ( LZMA provides high
compression ratio and very fast decompression.
7z ANSI-C Decoder is part of the LZMA SDK.
LZMA SDK is written and placed in the public domain by Igor Pavlov.
7zDecode.* - Low level 7z decoding
7zExtract.* - High level 7z decoding
7zHeader.* - .7z format constants
7zIn.* - .7z archive opening
7zItem.* - .7z structures
7zMain.c - Test application
How To Use
You can create .7z archive with 7z.exe, 7za.exe or 7zr.exe:
7z.exe a archive.7z *.htm -r -mx -m0fb=255
If you have big number of files in archive, and you need fast extracting,
you can use partly-solid archives:
7za.exe a archive.7z *.htm -ms=512K -r -mx -m0fb=255 -m0d=512K
In that example 7-Zip will use 512KB solid blocks. So it needs to decompress only
512KB for extracting one file from such archive.
Limitations of current version of 7z ANSI-C Decoder
- It reads only "FileName", "Size", "LastWriteTime" and "CRC" information for each file in archive.
- It supports only LZMA and Copy (no compression) methods with BCJ or BCJ2 filters.
- It converts original UTF-16 Unicode file names to UTF-8 Unicode file names.
These limitations will be fixed in future versions.
Using 7z ANSI-C Decoder Test application:
Usage: 7zDec <command> <archive_name>
e: Extract files from archive
l: List contents of archive
t: Test integrity of archive
7zDec l archive.7z
lists contents of archive.7z
7zDec e archive.7z
extracts files from archive.7z to current folder.
How to use .7z Decoder
Memory allocation
7z Decoder uses two memory pools:
1) Temporary pool
2) Main pool
Such scheme can allow you to avoid fragmentation of allocated blocks.
Steps for using 7z decoder
Use code at 7zMain.c as example.
1) Declare variables:
inStream /* implements ILookInStream interface */
CSzArEx db; /* 7z archive database structure */
ISzAlloc allocImp; /* memory functions for main pool */
ISzAlloc allocTempImp; /* memory functions for temporary pool */
2) call CrcGenerateTable(); function to initialize CRC structures.
3) call SzArEx_Init(&db); function to initialize db structures.
4) call SzArEx_Open(&db, inStream, &allocMain, &allocTemp) to open archive
This function opens archive "inStream" and reads headers to "db".
All items in "db" will be allocated with "allocMain" functions.
SzArEx_Open function allocates and frees temporary structures by "allocTemp" functions.
5) List items or Extract items
Listing code:
Use SzArEx_GetFileNameUtf16 function. Look example code in C\Util\7z\7zMain.c file.
Extracting code:
SZ_RESULT SzAr_Extract(
CArchiveDatabaseEx *db,
ILookInStream *inStream,
UInt32 fileIndex, /* index of file */
UInt32 *blockIndex, /* index of solid block */
Byte **outBuffer, /* pointer to pointer to output buffer (allocated with allocMain) */
size_t *outBufferSize, /* buffer size for output buffer */
size_t *offset, /* offset of stream for required file in *outBuffer */
size_t *outSizeProcessed, /* size of file in *outBuffer */
ISzAlloc *allocMain,
ISzAlloc *allocTemp);
If you need to decompress more than one file, you can send these values from previous call:
You can consider "outBuffer" as cache of solid block. If your archive is solid,
it will increase decompression speed.
After decompressing you must free "outBuffer":
6) call SzArEx_Free(&db, allocImp.Free) to free allocated items in "db".
Memory requirements for .7z decoding
Memory usage for Archive opening:
- Temporary pool:
- Memory for uncompressed .7z headers
- some other temporary blocks
- Main pool:
- Memory for database:
Estimated size of one file structures in solid archive:
- Size (4 or 8 Bytes)
- CRC32 (4 bytes)
- LastWriteTime (8 bytes)
- Some file information (4 bytes)
- File Name (variable length) + pointer + allocation structures
Memory usage for archive Decompressing:
- Temporary pool:
- Memory for LZMA decompressing structures
- Main pool:
- Memory for decompressed solid block
- Memory for temprorary buffers, if BCJ2 fileter is used. Usually these
temprorary buffers can be about 15% of solid block size.
7z Decoder doesn't allocate memory for compressed blocks.
Instead of this, you must allocate buffer with desired
size before calling 7z Decoder. Use 7zMain.c as example.
_SZ_ALLOC_DEBUG - define it if you want to debug alloc/free operations to stderr.