Most C compilers now have support for at least some of the features of C99. However, there has been less support from vendors such as Microsoft and Borland that have mainly focused on C++.
GCC, despite its extensive C99 support, is still not a completely compliant implementation (44 features done); as of May 2010[update], 6 of the features are missing or do not work correctly.[1]
The Open Watcom C compiler implements the most-used parts of the standard. However, they are enabled only through an undocumented command-line switch.[2]
According to Sun Microsystems, Sun Studio (which is downloadable without charge) now supports the full C99 standard.[3]
The C interpreter Ch supports major C99 features [4] and it is available without charge in Windows, Linux, Mac OS X, Solaris, QNX and FreeBSD.
The compiler within Pelles C supports most C99 features.
Intel C++ compiler supports some of the most important C99 features.
The free AMD x86 Open64 Compiler Suite has C99 support equal to that of GCC.[5]
The Tiny C Compiler supports most of C99 except complex numbers and variable length arrays.
The Portable C compiler is also working to become C99 compliant.
Clang is C99 compliant, except for the C99 floating-point pragmas.[6]