id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc
390	Add C preprocessor defintion identifying the Multics C compiler	johnsonjh.dev@…	Eric Swenson	"I propose that we define `__COMPILER_MULTICSC__` automatically, which programs can use to determine that they are being built with the ""Multics C Compiler"".  This is in-line with the KCC C compiler for TOPS-20 defining `__COMPILER_KCC__`, etc.  (Clang does similar, defining `__clang_version__` to the version in use, Vbcc defines `__VBCC__`, etc.)

Currently Multics C automatically defines ""`multics`"" which can be used to identify **the platform**, but nothing for identification of **the specific compiler**.  This would be the equivalent of passing the `-def __COMPILER_MULTICSC__` control argument to `cc`.

Because Multics C is known to be somewhat deficient, it's common to have various Multics C-specifc workarounds in C programs, even those written extremely portably, and guard those workarounds with `#ifdef multics`.

Once we have the future theoretical bug-free non-Multics C-based compiler, whatever it might end up being, it will become important to be able to differentiate between the different compilers at compile-time.  While those compilers will of course identify themselves in a similar fashion, it is still useful to differentiate Multics C.

We have the source code to the `cc` compiler driver (see `>sl3p>cc>s>bound_cc_commands.s.archive>c_compile.pl1`) so making this addition would be trivial, and there would be no effect on any existing C code that does not have knowledge of or check for the definition.

Programs that do wish to use the definition could do so:

`#ifdef multics`
`      /* Multics OS code */`
`# ifdef __COMPILER_MULTICSC__`
`      /* Multics C Compiler specific code */`
`# else`
`      /* Other Multics compilers */`
`# endif`
`#else`
`      /* non-Multics OS code */`
`#endif`

A real-life example of a program that would benefit is http://gitlab.com/dps8m/crc - there are 12 checks for the `multics` definition and of those 12, only **one** is really checking for ""Multics, the operating system"".  The other 11 uses are actually specific to ""Multics C, the compiler""."	enhancement	new	minor	MR12.9	Tools	MR12.9			Eric Swenson