解析空文件yacc/lex时没有错误 [英] no error while parsing empty file yacc/lex

问题描述

我有一个从yacc/lex生成的解析器.对于我设定的所有规则(一种情况除外)，它都可以正常工作.

I have a parser with me generated from yacc/lex. It is working fine for all the rules I have set except one case.

如果此解析器正在解析的文件为空，则会产生错误.我想添加规则，以便在文件为空时不给出错误.我没有在我的.l/.y文件中添加任何检查.

If file is empty which this parser is parsing it gives error. I want to add rule so that it does not give error when file is empty. I have not added any checks for that in either of my .l/.y file.

如何使用YACC/LEX做到这一点?

How can this be done with YACC/LEX?

预先感谢！

推荐答案

词法分析器应识别输入的结尾并相应地返回令牌(即EOF).

The lexer should recognize the end of input and return a token accordingly (i.e. EOF).

您的语法的开始规则如下:

Your grammar's start rule could look like this:

%start program

...

program : EOF 
        | instructions EOF
        ;

正如艾拉·巴克斯特(Ira Baxter)所指出的那样，简单的空"规则也足够了. GNU野牛手册为此提供了一个示例:

As Ira Baxter pointed out a simple "empty" rule would also suffice. The GNU bison manual provides an example for this:

input   : /* empty */
        | input line
        ;

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