The LPC preprocessor
A preprocessor directive is a line whose first non-whitespace character
is #. Directives are not statements: they instruct the compiler while
it reads the file. A directive owns its whole logical line; ending a
line with a backslash (\) continues the directive onto the next line,
and comments may appear on directive lines.
Preprocessing in FluffOS is integrated into the compiler's single scan of the source — there is no separate preprocessing pass — but the semantics are the conventional C-family ones described here.
Directives
| Directive | Purpose |
|---|---|
#define | Define an object-like or function-like macro. |
#undef | Remove a macro definition. |
#include | Splice another file into the compile. |
#if / #elif / #else / #endif | Conditional compilation over constant expressions. |
#ifdef / #ifndef | Conditional compilation on whether a macro is defined. |
#pragma | Toggle per-file compiler flags. |
#error text | Abort the compile with text as the error message. |
#warn text | Emit text as a compiler warning; does not fail the compile (and is suppressed by #pragma no_warnings). |
#echo text | Print text to the driver's stderr during the compile. |
#line N ["file"] | Override the reported line number (and optionally file name) for subsequent diagnostics. # N is accepted as a synonym. |
An unknown directive is a compile error.
Predefined macros
The driver predefines macros describing itself and its configuration:
__FILE__, __LINE__, __DIR__, FLUFFOS, MUDOS, MUD_NAME,
__VERSION__, MAX_INT, MIN_INT, MAX_FLOAT, MIN_FLOAT,
__ARCH__, plus one __PACKAGE_NAME__-style macro per compiled-in
package and one __FEATURE__-style macro per enabled option, among
others. Predefined macros are immutable: both #define and
#undef of a predefined name are compile errors.
__FILE__ and __DIR__ name the object being compiled, even when
they appear inside an #included header. That is the long-standing
MudOS/FluffOS meaning: a shared header that uses __DIR__ builds paths
relative to the including object, not the header itself. __LINE__ is
the live scan position (so it does track the header's lines). #line
overrides the reported line (and optionally the diagnostic file name)
but does not change __FILE__/__DIR__.