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Watcom C/C++

  (Redirected from Open Watcom)

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 as freeware under the name Open Watcom C/C++. It features tools for developing and debugging code for MS-DOS, OS/2, Windows, Linux operating systems, which are based upon x86, IA-32, x86-64 compatible processors.

Open Watcom C/C++
Watcom logo.png
Original author(s) Watcom, Sybase,
SciTech Software
Developer(s) Open community
Initial release January 8, 2003;
15 years ago
Stable release
1.9 / June 2, 2010;
7 years ago
Preview release
2.0 / April 2, 2015;
2 years ago
Development status Active
Written in C, C++
Operating system Cross-platform
Platform x86, IA-32, x86-64
Size 66 to 84 MB
Type Integrated development environment
License Sybase Open Watcom Public License version 1.0



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.

The Open Watcom C/C++ version 1.4 release on December 2005 introduced Linux x86 as an experimental target, supported from NT or OS/2 host platforms. There is code for an abandoned QNX version, but libraries necessary for it to be compiled could not be released as open source.[citation needed]

Stable version 1.9 was released in June 2010.[1]

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).[2]

Release historyEdit

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

Date Product Notes
1984 Waterloo C for S/370
1985 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
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 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
1998 Watcom C/C++ 11.0B
1999 Sybase issues end-of-life notice for Watcom C/C++ 11.0
2000 Sybase announces open sourcing of Watcom tools
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. Open Watcom ported to 64-bit hosts (Windows and Linux), Resource compiler and Resource editor support WIN64 executables, built-in text editor, 2-phase build system, DOS version of tools support long filenames (LFN), numerous fixes.[2]


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."[4]


The compiler can be operated from, and generate executable code for, the DOS (MS-DOS, FreeDOS), OS/2, Windows, Linux operating systems. It also supports NLM targets for Novell NetWare. There is ongoing work to extend the targeting to Linux[5] 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 MS-DOS computer games such as Doom,[3] Descent,[3] Duke Nukem 3D,[3] and Rise of the Triad[6] were built using Watcom C/C++, some such as ROTT using the DOS/4GW protected mode extender with the Watcom compiler.

It was used to port the game Retro City Rampage to MS-DOS in 2015.[7]

It is used by VirtualBox to compile the BIOS.[8]


There is an unofficial fork[9] of Open Watcom V2 on GitHub.[10] A variant of the 16bit DOS CRT library startup was created with WASM.[11]


Open Watcom's syntax supports many conventions introduced by other compilers, such as Microsoft's and Borland's, including differing conventions 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.[12]

The compiler currently doesn't support any new major C11 features, though the C library does include "Safe C" functions. It is specified in ISO/IEC TR 24731-1[13][14] and known as "Bounds-checking interfaces (Annex K)" in C11. Some function name examples are strcpy_s(), memcpy_s(), printf_s().[15] This library was released along with Open Watcom 1.5 in April 2006.

See alsoEdit


External linksEdit