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https://github.com/fluffos/fluffos
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d38dc2c833
A '//' comment after a #define body was captured INTO the stored macro body. Expansion buffers carry no newline to end it, so when the macro expanded inside a spliced line (a function-like macro's substituted body, as in the report's MIN(credits, m[e][CREDITS])), the '//' ate the rest of the splice and the parse failed with a baffling 'unexpected ;' attributed to the outer macro. The same missed strip made '#undef X // why' erase nothing and '#ifdef X // why' look up the wrong name and silently take the false branch. Comments are whitespace (C translation phase 3). dispatch_directive now strips them from the payload before parsing for #define (name, params, body -- body also right-trimmed so a stripped comment can't turn '1' vs '1 ' into a spurious redefinition warning), #undef, #ifdef, #ifndef, and #pragma (word-list payload); #if/#elif already stripped. strip_directive_comments() now folds a block comment to ONE space instead of nothing, so '1 -/*c*/-1' keeps its token boundaries instead of pasting '--'. #error/#warn/#echo payloads stay raw. Covered by five new Preprocessor unit tests (the report's repro shape, paste-prevention via #if branch selection, param-list comment, testsuite/single/tests/compiler/preprocessor.lpc; documented in docs/lpc/preprocessor/define.md. Fixes #1240 Claude-Session: https://claude.ai/code/session_016FMBJLkpkpVpZdz6PWzeWe Co-authored-by: Claude <noreply@anthropic.com>
101 lines
2.8 KiB
Markdown
101 lines
2.8 KiB
Markdown
---
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title: preprocessor / define
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---
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# #define and #undef
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`#define` creates a **macro**: a name that is replaced by a body of
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text wherever it appears later in the file.
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## Object-like macros
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```c
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#define MAX_HP 100
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#define GREETING "Welcome to " MUD_NAME
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```
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Every later occurrence of the name (as a whole identifier — not inside
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strings, comments, or longer identifiers) is replaced by the body.
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## Function-like macros
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A parameter list attached **directly** to the name (no space before
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`(`) makes the macro function-like:
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```c
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#define SQUARE(x) ((x) * (x))
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#define MSG(who, text) tell_object(who, text "\n")
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```
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Arguments are collected with full nesting awareness — commas inside
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parentheses, strings, or character literals do not split arguments.
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Parenthesize parameters in the body (as above) to avoid precedence
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surprises at the use site.
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Inside a macro body, `#param` produces the argument's text as a string
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literal, and `a ## b` pastes two tokens together. `##` may not appear
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at the very start or end of a body.
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## Expansion and rescan
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A macro's body is rescanned after substitution, so macros may reference
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other macros freely. A macro that (directly or indirectly) references
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itself stops expanding at the self-reference instead of recursing
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forever, as in C.
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Because `#if` expressions are evaluated over the same token stream,
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arithmetic keeps C precedence across macro boundaries:
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```c
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#define X 1+1
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#if X*2 == 3 // 1+1*2 -- true
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```
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## Multi-line macros
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End a line with `\` to continue the definition:
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```c
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#define LONG_MACRO(x) do { \
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write(x); \
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} while (0)
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```
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A block comment opened on a directive line may also span lines — it
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reads as whitespace and does not end the directive, so both of these
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define `WARNING_LEVEL` as `1`:
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```c
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#define WARNING_LEVEL 1 /* change to a higher value to
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show more warnings */
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#define WARNING_LEVEL 1 // single-line form
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```
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Text after the comment's close on its final line still belongs to the
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directive, matching C.
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Comments on a directive line are whitespace, never part of the macro:
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a trailing `//` or `/* */` after the body (or after the name on
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`#undef`/`#ifdef`) is stripped before the directive is parsed, and a
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block comment inside the body separates tokens like a space would:
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```c
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#define CREDITS "credits" // key into the economy mapping
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```
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## Redefinition
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Redefining a macro with a **different** body is allowed: the compiler
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emits a warning (with a note pointing at the previous definition) and
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the new definition takes effect. Redefining with an identical body is
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silent. Redefining or `#undef`-ing a **predefined** macro (`__FILE__`,
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`FLUFFOS`, ...) is a compile error.
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## #undef
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```c
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#undef MAX_HP
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```
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Removes a user macro definition; the name is ordinary text again.
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`#undef` of an unknown name is harmless.
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