Lex和Yacc问题与评论

本文介绍了Lex和Yacc问题与评论的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我正在尝试查找问题的根本原因.我有以下行需要解析-

I am trying to locate the root cause of an issue. I have the following line that needs to be parsed -

sample format "string";

sample和format需要标记的地方，并且需要将反向逗号中的任何内容提供给Parser文件. 但是有一个问题，如果我在字符串中有一个perl样式注释#，那么我会得到一个错误.

Where sample and format need to be tokenized and whatever is in the inverted commas needs to be provided to the Parser file. There is a catch however, if I have a perl style comment # inside the string, then I get an error.

在lexer.l中，我有以下内容-

stringIdentifier [^"]+ <STRING_S>{stringIdentifier} { strncpy(yylval.str, yytext,1023); yylval.str[1023] = '\0'; return IDENTIFIER; } <*>"//".* { } <*>"#".* { } <INITIAL>{s}{a}{m}{p}{l}{e} { BEGIN(SAMPLE_S); return SAMPLE; } <SAMPLE_S>{f}{o}{r}{m}{a}{t} { return FORMAT; } <SAMPLE_S>"\"" { BEGIN(STRING_S); return INVERTED_COMMA; } <STRING_S>"\"" { BEGIN(INITIAL); return INVERTED_COMMA; }

在Parser.y中，我有以下规则:

pass : SAMPLE FORMAT INVERTED_COMMA IDENTIFIER INVERTED_COMMA { };

但是，当我输入sample format "abc;"时，它可以工作，但是，当我在字符串中添加注释字符#时，它会失败.您能帮忙吗

However, when I give sample format "abc;" it works, however, when I add a comment character # in the string it fails. Could you please help with this

推荐答案

答案在于您使用默认 开始条件的方式.快速阅读 lex/flex手册.

The answer lies in the way you have used the default start conditions. A quick read of the lex/flex manual explains their operation.

<*>表示在每种状态下均应用以下模式.这包括在字符串内部，该字符串由S_STRING状态指示.要停止注释模式在字符串内的运行，您需要从<*>中排除 S_STRING状态.您可以通过列出所有其他适用的状态来实现此目的，在您的示例中，这些状态将枚举为<INITIAL,S_SAMPLE>.注释规则将变为:

The <*> means that the following pattern is applied in every state. This includes inside a string, which is indicated by the S_STRING state. To stop the comment pattern operating inside the string you need to exclude the S_STRING state from <*>. You can do this by listing all the other applicable states, which enumerate, in your example, to <INITIAL,S_SAMPLE>. The comment rules then become:

<INITIAL,SAMPLE_S>"//".* { } <INITIAL,SAMPLE_S>"#".* { }

就是这样.现在可以使用了！ (我已经对其进行过测试)

And that's it. It now works! (I have tested it BTW)