Flex:未被识别的规则`(？s：.)

Question

在我的flex程序中，我无法使用任何这些正则表达式。其中任何一个的使用都会产生unrecognized rule错误。

%{
#include<stdio.h>
%}

%option nodefault
%option noyywrap
%option outfile="scanner.c"

%%

(?i:a) printf("rule1");

(?s:.) printf("rule2");

(?x:a b) printf("rule3");

(?#foo) printf("rule4");

[a-z]{-}[aeiou] printf("rule5");

%%

所有这些都在这文档中得到了很好的定义。我很困惑，我是不是用错了flex变体！我使用的是带有GnuWin32 flex v2.5.4的windows机器。

这是正在生成的错误：

$flex misc/test_lexer.l
"misc/test_lexer.l", line 11: unrecognized rule
"misc/test_lexer.l", line 11: unrecognized rule
"misc/test_lexer.l", line 11: unrecognized rule
"misc/test_lexer.l", line 11: unrecognized rule
"misc/test_lexer.l", line 11: unrecognized rule
"misc/test_lexer.l", line 11: unrecognized rule
"misc/test_lexer.l", line 13: unrecognized rule
"misc/test_lexer.l", line 13: unrecognized rule
"misc/test_lexer.l", line 13: unrecognized rule
"misc/test_lexer.l", line 13: unrecognized rule
"misc/test_lexer.l", line 13: unrecognized rule
"misc/test_lexer.l", line 13: unrecognized rule
"misc/test_lexer.l", line 15: unrecognized rule
"misc/test_lexer.l", line 15: unrecognized rule
"misc/test_lexer.l", line 15: unrecognized rule
"misc/test_lexer.l", line 15: unrecognized rule
"misc/test_lexer.l", line 15: unrecognized rule
"misc/test_lexer.l", line 17: unrecognized rule
"misc/test_lexer.l", line 17: unrecognized rule
"misc/test_lexer.l", line 17: unrecognized rule
"misc/test_lexer.l", line 17: unrecognized rule
"misc/test_lexer.l", line 17: unrecognized rule
"misc/test_lexer.l", line 17: unrecognized rule
"misc/test_lexer.l", line 17: unrecognized rule
"misc/test_lexer.l", line 19: unrecognized rule
"misc/test_lexer.l", line 19: unrecognized rule
"misc/test_lexer.l", line 19: unrecognized rule
"misc/test_lexer.l", line 19: unrecognized rule
"misc/test_lexer.l", line 19: unrecognized rule
"misc/test_lexer.l", line 19: unrecognized rule
"misc/test_lexer.l", line 19: unrecognized rule
"misc/test_lexer.l", line 19: unrecognized rule
"misc/test_lexer.l", line 19: unrecognized rule
"misc/test_lexer.l", line 19: unrecognized rule

Answer 1

如果要使用这些构造，则需要更新flex安装。

Flex2.5.4是25年前发布的，它没有实现{-}，也没有实现任何(?:...)语法。

您引用的手册也不是当前版本，它指定：

这个版本的flex手动文档的flex版本为2.6.3。最后一次更新是在2017年1月13日。

Flex v2.5.4确实实现了/尾随上下文操作符，这个操作符在这个问题的原始版本中。但是请注意，/不能在括号内使用，而且由于flex通常在宏展开周围添加括号，所以/也不能用于宏展开。