author Ryan C. Gordon <>
Fri, 27 Mar 2009 15:10:42 -0400
changeset 972 254427fc42ab
parent 917 lzma/7zC.txt@d299a58a274f
permissions -rw-r--r--
Moved directory structure around.

7z ANSI-C Decoder 4.48

7z ANSI-C Decoder 4.48 Copyright (C) 1999-2006 Igor Pavlov

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.


Read lzma.txt for information about license.


7zAlloc.*    - Allocate and Free
7zBuffer.*   - Buffer structure
7zCrc.*      - CRC32 code
7zDecode.*   - Low level memory->memory decoding
7zExtract.*  - High level stream->memory decoding
7zHeader.*   - .7z format constants
7zIn.*       - .7z archive opening
7zItem.*     - .7z structures
7zMain.c     - Test application
7zMethodID.* - MethodID structure
7zTypes.h    - Base types and constants

How To Use

You must download 7-Zip program from

You can create .7z archive with 7z.exe or 7za.exe:

  7za.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

.7z Decoder can be compiled in one of two modes:

1) Default mode. In that mode 7z Decoder will read full compressed 
   block to RAM before decompressing.
2) Mode with defined _LZMA_IN_CB. In that mode 7z Decoder can read
   compressed block by parts. And you can specify desired buffer size. 
   So memory requirements can be reduced. But decompressing speed will 
   be 5-10% lower and code size is slightly larger.

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 ISzInStream interface */
  CArchiveDatabaseEx db;       /* 7z archive database structure */
  ISzAlloc allocImp;           /* memory functions for main pool */
  ISzAlloc allocTempImp;       /* memory functions for temporary pool */

2) call InitCrcTable(); function to initialize CRC structures.

3) call SzArDbExInit(&db); function to initialize db structures.

4) call SzArchiveOpen(inStream, &db, &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.
SzArchiveOpen function allocates and frees temporary structures by "allocTemp" functions.

5) List items or Extract items

  Listing code:
      UInt32 i;
      for (i = 0; i < db.Database.NumFiles; i++)
        CFileItem *f = db.Database.Files + i;
        printf("%10d  %s\n", (int)f->Size, f->Name);

  Extracting code:

  SZ_RESULT SzExtract(
    ISzInStream *inStream, 
    CArchiveDatabaseEx *db,
    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 SzArDbExFree(&db, allocImp.Free) to free allocated items in "db".

Memory requirements for .7z decoding 

Memory usage for Archive opening:
  - Temporary pool:
     - Memory for compressed .7z headers (if _LZMA_IN_CB is not defined)
     - 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 compressed solid block (if _LZMA_IN_CB is not defined)
     - 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. 

If _LZMA_IN_CB is defined, 7z Decoder will not allocate memory for 
compressed blocks. Instead of this, you must allocate buffer with desired 
size before calling 7z Decoder. Use 7zMain.c as example.

EXIT codes

7z Decoder functions can return one of the following codes:

#define SZ_OK (0)
#define SZE_DATA_ERROR (1)
#define SZE_CRC_ERROR (3)

#define SZE_NOTIMPL (4)
#define SZE_FAIL (5)


LZMA Defines

_LZMA_IN_CB       - Use special callback mode for input stream to reduce memory requirements

_SZ_FILE_SIZE_32  - define it if you need only support for files smaller than 4 GB
_SZ_NO_INT_64     - define it if your compiler doesn't support long long int or __int64.

_LZMA_PROB32      - it can increase LZMA decompressing speed on some 32-bit CPUs.

_SZ_ALLOC_DEBUG   - define it if you want to debug alloc/free operations to stderr.