c - Flex And Bison, detecting macro statements (newbie) -


i want teach flex & bison detect macro definitions in pure c. i'am adding function existing parser form here. parser good, lacks macro functionality. did add #include , pragma macros detection, selection macroses have problems, code in parser:

macro_selection_variants     : macro_compound_statement     | include_statement     | pragma_statement     | macro_selection_statement     | statement     ; macro_selection_statement     : macro_ifdef identifier macro_selection_variants macro_endif     | macro_ifdef identifier  macro_selection_variants macro_else macro_selection_variants macro_endif     | macro_ifndef identifier  macro_selection_variants macro_endif     | macro_ifndef identifier  macro_selection_variants macro_else macro_selection_variants macro_endif     ;

statement declared so:

 statement     : labeled_statement          | compound_statement     | expression_statement     | selection_statement     | iteration_statement     | jump_statement         ;

and lexer part macroses is:

"#ifdef"        { count(); return(macro_ifdef); } "#ifndef"       { count(); return(macro_ifndef); } "#else"         { count(); return(macro_else); } "#endif"        { count(); return(macro_endif); }

so problem 2 reduce/reduce errors because i'm trying use statement in macro_selection_statement. need use statement in macro selection block, because blocks can have variables definitions likes so:

#ifdef user #include "user.h"  int some_var;  char some_text[]="hello";     #ifdef 1         int two=0;     #endif #endif

what right move here? because read %expect -rr n bad thing reduce warnings.

you cannot expect implement preprocessor (properly) inside of c grammar. needs *pre*processor; is, reads program text, , output sent c grammar.

it possible (mostly) avoid doing second lex pass, since (in theory) preprocessor can output tokens rather stream of characters. work bison 2.7-or-better "push parser", might want give try. traditional approach stream of characters, may easier.

it's important remember replacement text of macro, arguments macro, have no syntactic constraints. (or no constraints.) following entirely legal:

#define open { #define close } #define say(whatever) puts(#whatever);  #include <stdio.h>  int main(int argc, char** argv) open say(===>) return 0; close

and that's start :)


Comments

Post a Comment

Popular posts from this blog

Python Kivy ListView: How to delete selected ListItemButton? -

Image
i'm trying learn kivy building simple todo-list app suggested dusty phillips, author of book "creating apps in kivy". this code far: from kivy.app import app kivy.uix.boxlayout import boxlayout kivy.properties import objectproperty kivy.uix.listview import listitembutton class taskbutton(listitembutton): pass class todoroot(boxlayout): task_input = objectproperty() task_list = objectproperty() def add_task(self): self.task_list.adapter.data.extend([self.task_input.text]) self.task_list._trigger_reset_populate() def del_task(self): pass class todoapp(app): def build(self): return todoroot() if __name__ == '__main__': todoapp().run() and kv file: #: import main todo #: import listadapter kivy.adapters.listadapter.listadapter #: import listitembutton kivy.uix.listview.listitembutton todoroot: <todoroot>: orientation: "vertical" task_input: task_input_view t...
Read more

ruby - How do I merge two hashes into a hash of arrays? -

http://codepad.org/wmyzqlis i'd merge these 2 arrays: a = { :a => 'a', :b => 'b', :d => 'd' } b = { :a => '1', :b => 'b', :c => 'c' } into hash looks this: {:a => ["a", "1"], :b => ["b", "b"], :c => [nil, "c"], :d => ["d", nil] } this doesn't work: p a.merge(b) { |k, v1, v2| [v1, v2] } # {:c=>"c", :a=>["a", "1"], :b=>["b", "b"], :d=>"d"} it's because hash#merge call block duplicate keys. a = { :a => 'a', :b => 'b', :d => 'd' } b = { :a => '1', :b => 'b', :c => 'c' } hash[(a.keys|b.keys).map { |key| [key, [a.fetch(key, nil), b.fetch(key, nil)]] }] # => {:a=>["a", "1"], :b=>["b", "b"], :d=>["d", nil], :c=>...
Read more