Watcom C/C++

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Open Watcom C/C++
Original author(s)Watcom
Developer(s)Sybase, SciTech Software
Initial release1988;
36 years ago
Stable release
1.9 / June 2, 2010;
13 years ago
Preview release
2.0 / December 1, 2022;
17 months ago
Written inC, C++
Operating systemDOS, Windows, OS/2, Linux
Platformx86, IA-32, x86-64
Size66–84 MB
TypeIntegrated development environment
LicenseSybase Open Watcom Public License version 1.0

Watcom C/C++ (currently Open Watcom C/C++) is an integrated development environment (IDE) product from Watcom International Corporation for the C, C++, and Fortran programming languages. Watcom C/C++ was a commercial product until it was discontinued, then released under the Sybase Open Watcom Public License as Open Watcom C/C++. It features tools for developing and debugging code for DOS, OS/2, and Windows, Linux operating systems, which are based upon 16-bit x86, 32-bit IA-32, or 64-bit x86-64 compatible processors.


Though no longer sold commercially by Sybase, the Watcom C/C++ compiler and the Watcom Fortran compiler have been made available free of charge as the Open Watcom package.

Stable version 1.9 was released in June 2010.[2][3]

A forked version 2.0 beta was released that supports 64-bit hosts (Windows and Linux), built-in text editor, 2-phase build system, and the DOS version supports long filenames (LFN).[4]

Release history[edit]

The Open Watcom Wiki has a comprehensive history.[5][3]

Release history table
Date Product Notes
1984 Waterloo C for S/370
  • Work on current code generator codebase started
1988 Watcom C 6.0
  • DOS host and target only
  • Included a debugger and full set of runtime libraries
  • Generated better code than other compilers at the time
  • Watcom C Version 6.5 contained Graphics Library similar to Microsoft Graphics Library
  • Real mode support only[citation needed]
1989 Watcom C 7.0
1989 Watcom C 7.0/386
1990 Watcom C 8.0
1990 Watcom C 8.0/386
1991 Watcom C 8.5
1991 Watcom C 8.5/386
1992 Watcom C 9.0
1992 Watcom C 9.0/386
  • OS/2 2.0 host and target support
  • 486 optimizations
  • Based pointer support
Watcom C 9.01/386
1993 Watcom C/C++ 9.5
1993 Watcom C/C++ 9.5/386
1994 Watcom C/C++ 10.0
1995 Watcom C/C++ 10.5
1996 Watcom C/C++ 10.6
1997 Q1[6] Watcom C/C++ 11.0
  • Namespace, RTTI, and new style cast support in C++ compiler
  • 64-bit integer support
  • Multi-byte character support in libraries
  • Incremental linking support
  • COFF and ELF object file support in linker and librarian
  • Microsoft clone tools added
  • DLL based tools for better IDE integration
  • MMX support, including debugging
  • Pentium Pro optimizations, including branch prediction
  • Novell NLM support
1998 Watcom C/C++ 11.0B
  • Sybase announces open sourcing of Watcom tools[8]
2001-09-27 Watcom C/C++ 11.0c Beta
2002-12-21 Watcom C/C++ 11.0c
2003-01-28 Open Watcom 1.0
2003-08-12 Open Watcom 1.1
2004-01-07 Open Watcom 1.2
2004-08-03 Open Watcom 1.3
2005-12-14 Open Watcom 1.4
2006-04-26 Open Watcom 1.5
2006-12-15 Open Watcom 1.6
2007-08-18 Open Watcom 1.7
2007-10-23 Open Watcom 1.7a
2009-02-21 Open Watcom 1.8
2010-06-02 Open Watcom 1.9
  • Current official version
2015-04-02 Open Watcom 2.0 Beta
  • GitHub V2 fork, numerous fixes[4]
  • Open Watcom ported to 64-bit hosts (Windows and Linux)
  • Resource compiler and Resource editor support WIN64 executables
  • built-in text editor
  • two-phase build system
  • DOS version of tools support long filenames (LFN)


The Open Source Initiative has approved the license as open source, but Debian, Fedora and the Free Software Foundation have rejected it because "It requires you to publish the source code publicly whenever you “Deploy” the covered software, and “Deploy” is defined to include many kinds of private use."[9]


The compiler can be operated from, and generate executable code for, the DOS, OS/2, Windows, Linux operating systems. It also supports NLM targets for Novell NetWare. There is ongoing work to extend the targeting to Linux[10] and modern BSD (e.g., FreeBSD) operating systems, running on x86, PowerPC, and other processors.

The code is portable and, like many other open source compiler projects such as GCC or LCC the compiler backend (code generator) is retargetable.


In the mid-1990s some of the most technically ambitious DOS computer games such as Doom,[5] Descent,[5] Duke Nukem 3D,[5] Rise of the Triad,[11] and Tomb Raider were built using Watcom C/C++ using the DOS/4GW protected mode extender with the Watcom compiler.

It was used to port the game Retro City Rampage to DOS in 2015.[12]

It is used by VirtualBox to compile the BIOS.[13]

Current development for FreeDOS requires that all C source code must be compilable by Open Watcom C.[14]

Open Watcom is the recommended compiler for application and driver development for the OS/2-based ArcaOS operating system.[15]


There is an unofficial fork[16] of Open Watcom V2 on GitHub.[17] A variant of the 16bit DOS CRT library startup was created with WASM.[18]


Open Watcom's syntax supports many conventions[which?] introduced by other compilers, such as Microsoft's and Borland's, including differing conventions[which?] regarding (for instance) the number of leading underscores on the "asm" tag. Code written specifically for another compiler rather than standard-compliant C or C++ will often compile with the Watcom compiler.

The compiler supports C89/C90 standards by default.

Open Watcom supports partial compatibility with the C99 standard. It implements the most commonly used parts of the standard. However, they are enabled only through the undocumented command-line switch "-za99". Three C99 features have been bundled as C90 Extension since pre-v1.0: C++ style comments (//), flexible array members, trailing comma allowed in enum declaration.[19]

The compiler currently doesn't support any new[when?] major C11 features, though the C library does include "Safe C" functions. It is specified in ISO/IEC TR 24731-1[20][21] and known as "Bounds-checking interfaces (Annex K)" in C11. Some function name examples are strcpy_s(), memcpy_s(), printf_s().[22] This library was released along with Open Watcom 1.5 in April 2006.

See also[edit]


  1. ^ "Release 2022-12-01 Build · open-watcom/open-watcom-v2". GitHub.
  2. ^ "Latest Release (June 2010) - Open Watcom". OpenWatcom.org wiki. Archived from the original on January 18, 2015.
  3. ^ a b "C Compiler Release Changes". Open Watcom. March 9, 2010. Archived from the original on February 3, 2015.
  4. ^ a b List of main differences of v1.9 to v2.0 Beta.
  5. ^ a b c d History - Open Watcom. OpenWatcom.com wiki.
  6. ^ SYBASE INC. ANNOUNCES WATCOM C/C++ VERSION 11.0 Includes New Support For MMX Technology and Improved C++ language Support
  7. ^ End of Life Notice for Watcom C/C++ Version 11.0
  8. ^ Sybase to Open Source Watcom C/C++ and Fortran Compilers - SciTech Software Selected as Official Maintainer for the Open Watcom Project
  9. ^ Free Software Foundation. "Various Licenses and Comments about Them". GNU Operating System. Retrieved Dec 23, 2014.
  10. ^ Installing Open Watcom on Linux - Open Watcom. OpenWatcom.org wiki.
  11. ^ "RotT was written in Watcom C++ v10.0 with the Rational Systems DOS/4GW extender".
  12. ^ "How 5 years of burning ambition brought Retro City Rampage to DOS". Gamasutra. 10 July 2015.
  13. ^ "#12011 (Compiling BIOS requires Open Watcom compiler)– Oracle VM VirtualBox". www.virtualbox.org. Retrieved 2017-06-17.
  14. ^ "FreeDOS Spec". FreeDOS. Archived from the original on May 1, 2019.
  15. ^ "Information for developers". arcanoae.com. Retrieved 2020-09-06.
  16. ^ "Open Watcom V2 Fork".
  17. ^ "Open Watcom V2 Fork Project on GitHub". GitHub.
  18. ^ "pcdosasm.zip archive". 2010-07-27. Retrieved 2014-02-10. Modified Open Watcom C/C++ DOS 16-bit ..\STARTUP\DOS\CSTRT086.ASM code
  19. ^ "C99 compliance in Open Watcom". Retrieved 2020-11-30.
  20. ^ ISO/IEC TR 24731-1; Extension to the C Library, Part 1: Bounds-checking interfaces.
  21. ^ WG14 N1969 — "Updated Field Experience With Annex K — Bounds Checking Interfaces", Carlos O'Donell, Martin Sebor
  22. ^ "Open Watcom Safer C Library". Retrieved 2020-11-30.

Further reading[edit]

External links[edit]