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. However, they are enabled only through the undocumented command-line switch "-za99". It implements the most commonly used parts of the standard. Open Watcom supports partial compatibility with the C99 standard. The compiler supports C89/C90 standards by default. Code written specifically for another compiler rather than standard-compliant C or C++ will often compile with the Watcom compiler. 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. A variant of the 16bit DOS CRT library startup was created with WASM. There is an unofficial fork of Open Watcom V2 on GitHub.
Open Watcom is the recommended compiler for application and driver development for the OS/2-based ArcaOS operating system. Ĭurrent development for FreeDOS requires that all C source code must be compilable by Open Watcom C. It is used by VirtualBox to compile the BIOS. It was used to port the game Retro City Rampage to DOS in 2015.
In the mid-1990s some of the most technically ambitious DOS computer games such as Doom, Descent, Duke Nukem 3D, Rise of the Triad, and Tomb Raider were built using Watcom C/C++ using the DOS/4GW protected mode extender with the Watcom compiler.
The code is portable and, like many other open source compiler projects such as GCC or LCC the compiler backend (code generator) is retargetable. There is ongoing work to extend the targeting to Linux and modern BSD (e.g., FreeBSD) operating systems, running on x86, PowerPC, and other processors. It also supports NLM targets for Novell NetWare. The compiler can be operated from, and generate executable code for, the DOS, OS/2, Windows, Linux operating systems. 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." Design Main article: Sybase Open Watcom Public License