https://github.com/binarymelodies/msbasic-savefile-re
Reverse engineering Microsoft BASIC binary save formats
https://github.com/binarymelodies/msbasic-savefile-re
basic microsoft-basic qb quickbasic reverse-engineering vbdos
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Reverse engineering Microsoft BASIC binary save formats
- Host: GitHub
- URL: https://github.com/binarymelodies/msbasic-savefile-re
- Owner: BinaryMelodies
- License: gpl-3.0
- Created: 2025-06-21T09:05:37.000Z (9 months ago)
- Default Branch: main
- Last Pushed: 2025-06-24T16:36:11.000Z (9 months ago)
- Last Synced: 2025-09-02T19:45:04.378Z (7 months ago)
- Topics: basic, microsoft-basic, qb, quickbasic, reverse-engineering, vbdos
- Language: HTML
- Homepage:
- Size: 85 KB
- Stars: 1
- Watchers: 1
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE
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README
# Reverse engineering the binary save formats of Microsoft BASIC
This repository will be a collection of documents and scripts that help reverse engineering binary save formats of various Microsoft BASIC versions.
## QuickBASIC
The folder `qb` contains the current work for QuickBASIC versions 4.0, 4.5, 7.0, 7.1 as well as Visual Basic for MS-DOS.
It contains `doc.html`, documenting the file format as it is known, and a script `qb.py` that takes as argument the file name of a BASIC file, saved in binary format, and outputs a textual representation.
The output should be as close to the text format saved by QuickBASIC.
## Macintosh BASIC
Unlike the MS-DOS versions, QuickBASIC for Macintosh uses a tokenized file format, similar to GW-BASIC.
Like QuickBASIC, line numbers are optional, and variable names are stored in a table.
The script `mac.py` in the folder `mac` converts a Macintosh binary file into text output.
### Format of QuickBASIC binary files
The first byte is `F1` (hexadecimal) for tokenized files (`F0` for protected files, format unknown).
It is then followed by a series of lines.
Each line starts with a 16-bit big endian word, encoding the length of the line in bytes (including this 16-bit word).
The most significant bit is set if the line starts with a line number.
Then a single byte encodes the number of spaces (one less if it starts with a line number) preceding the first non-space character.
If the line has a line number (that is, the most significant bit of the initial 16-bit word is set), then a 16-bit big endian word follows, storing the number.
The line body then follows as a token stream, with bytes `20` to `7E` (hexadecimal) encoding their ASCII values.
Each line is then terminated by a null byte.
The last line is followed by a 16-bit null word, an impossible byte length for a line (it is always at least 2 bytes long).
Then the section containing identifier names follows.
It always starts on an even address, with a single null byte, followed by the identifiers.
Each identifier begins with a single byte, encoding the length of the identifier, followed by the characters of the identifier.
Identifiers are indexed by their number in the sequence: the first identifier is accessed as identifier 0, the second one as identifier 1, and so on.
For the various token types, see `mac.py` under the `mac` folder.
# Disclaimer
This work is done without any access to disassembly or internal documentation to the BASIC executables.
All information is provided as-is, with no warranty as to its correctness or usability.
However, the author believes the code produces generally correct output.
# Useful links
GW-BASIC, the predecessor to QuickBASIC, uses its own binary format, already documented in other places:
* [Documentation of the binary format](http://www.chebucto.ns.ca/~af380/GW-BASIC-tokens.html)
* [PC-BASIC documentation of the binary format](http://robhagemans.github.io/pcbasic/doc/2.0/#technical)