evv/gw-basic-2026

Files

Eremey Valetov 817c26f55f Fix TUI null-pointer crashes and add DOS build docs

Fix 6 crash paths when TUI screen buffer allocation fails (common on
16-bit DOS due to near-heap exhaustion):
- main.c: REPL and AUTO mode fall back to fgets-based line reader
- tui.c: tui_key_on/off/list return early if tui.screen is NULL

Add DOS build documentation to getting-started.md (16-bit and 32-bit
targets, running on FreeDOS). Fix stale version string (0.14.0 -> 0.16.0).

2026-04-10 10:09:22 -04:00

4.7 KiB

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Getting Started

Dependencies

C11 compiler (GCC or Clang)
CMake 3.10+
PulseAudio development library (libpulse-simple) -- optional, for SOUND/BEEP/PLAY

On Debian/Ubuntu:

sudo apt-get install build-essential cmake libpulse-dev

On Fedora/RHEL:

sudo dnf install gcc cmake pulseaudio-libs-devel

Building

git clone https://github.com/evvaletov/gw-basic-2026.git
cd gw-basic-2026
mkdir -p build && cd build
cmake .. && make

The binary is build/gwbasic.

Usage

Interactive Mode

Running ./gwbasic with no arguments launches the full-screen editor:

$ ./gwbasic
GW-BASIC 2026 0.16.0
(C) Eremey Valetov 2026. MIT License.
Based on Microsoft GW-BASIC assembly source.
Ok
PRINT 2+2
 4
Ok
FOR I=1 TO 5:PRINT I;:NEXT
 1  2  3  4  5
Ok

Use arrow keys to move the cursor freely. Press Enter on any screen line to re-enter it. F1-F10 insert common commands (F2 runs the program).

Running a Program File

./gwbasic tests/programs/prime_sieve.bas

Piped Input

echo '10 FOR I=1 TO 10:PRINT I*I;:NEXT' | ./gwbasic

Direct Mode Expressions

Type expressions and statements at the Ok prompt:

PRINT SIN(3.14159/2)
 1
A$="HELLO WORLD":MID$(A$,7,5)="BASIC":PRINT A$
HELLO BASIC

Command-Line Options

Usage: gwbasic [options] [file.bas]
Options:
  -f, --full         Use full terminal size (default: 25x80)
  -h, --help         Show this help
  --lpt DEVICE|FILE  Printer output destination (default: LPT1.TXT)
                     Use LPT1 or /dev/lp0 for real hardware
  -v, --version      Show version

Ahead-of-Time Compiler

gwbasic-compile translates .bas programs to C source, then optionally invokes GCC to produce native executables linked against libgwrt.a.

Basic Usage

# Emit C source to stdout
build/gwbasic-compile program.bas

# Compile to native executable
build/gwbasic-compile -c --runtime . program.bas

Compiler Options

Usage: gwbasic-compile [options] input.bas
Options:
  -o FILE        Output C source file (default: stdout)
  -c             Compile to executable (invoke gcc)
  -O LEVEL       GCC optimization level (default: 2)
  --keep-c       Keep generated C file (with -c)
  --runtime DIR  Path to runtime headers/library
  --warn         Static analysis warnings
  --safe         Runtime safety checks (implies --warn)
  --safe=sanitize  Above + address/UB sanitizers (with -c)

Memory Safety (`--warn` / `--safe`)

The --warn flag enables compile-time static analysis warnings:

Uninitialized variables -- variables used before their first assignment (via LET, FOR, READ, INPUT)
GOTO/GOSUB to nonexistent line -- jump targets that don't exist in the program
Unreachable code -- lines after unconditional GOTO/END/STOP that are not jump targets

The --safe flag (implies --warn) adds runtime safety checks to the generated C:

Integer overflow detection -- arithmetic on integer (%) variables uses checked functions (gw_int_add, gw_int_sub, gw_int_mul) that raise "Overflow" instead of silently wrapping, matching real GW-BASIC behavior
Enhanced array diagnostics -- subscript errors report the array name, subscript value, line number, and which dimension exceeded its bound
GOSUB stack diagnostics -- stack overflow reports the source line and current depth

The --safe=sanitize flag (with -c) additionally passes -fsanitize=address,undefined to GCC for full memory error detection.

# Warnings only (zero runtime cost)
build/gwbasic-compile --warn program.bas

# Runtime safety checks
build/gwbasic-compile --safe -c --runtime . program.bas

# Full sanitizer build (debugging)
build/gwbasic-compile --safe=sanitize -c --runtime . program.bas

Building for DOS / FreeDOS

GW-BASIC 2026 cross-compiles to DOS using OpenWatcom V2 (wcc / wcc386). Two targets are available:

16-bit real-mode (recommended for FreeDOS)

Produces a standalone 127KB MZ executable -- no DOS extender required.

wmake -f Makefile.dos16

Requires OpenWatcom V2 with 16-bit DOS target. Uses MEDIUM memory model (-mm): code can exceed 64KB, data must fit in 64KB.

32-bit DOS/4GW

Produces a 175KB LE executable requiring DOS4GW.EXE (265KB) at runtime. Also builds the compiler (GWBASCOM.EXE) and runtime library (GWRT.LIB).

wmake -f Makefile.dos

Running on FreeDOS

Copy GWBASIC.EXE (and DOS4GW.EXE for the 32-bit build) to your FreeDOS system. Run programs from the command line:

C:\> GWBASIC PROGRAM.BAS

Running without arguments launches the interactive editor. The 16-bit build disables the full-screen TUI editor due to near-heap constraints but batch mode and direct-mode input work normally.

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