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c-like comment in lex

Posted on 2009-04-03
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Last Modified: 2012-05-06
Hello,

How can i declare the c-like comments in my lexer?
i.e. single line comment  =  /* comment */

I did that :

\/\* . *\/\  line++;

but i get :

error: syntax error before . token
error: stray \ in program
error: stray \ in program

Thanks in advance for any help !
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Question by:unknown_
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Infinity08 earned 500 total points
ID: 24057854
The errors you get is because of extra \'s you have. The \ is used as an escape character, but there has to be something to escape after it. Notice that the error message says exactly that !

Note also that C-style comments are not single-line comments - they can span multiple lines !

C-style comments are usually handled a bit differently. See for example how they did it in this lex specification for ANSI C :

        http://www.lysator.liu.se/c/ANSI-C-grammar-l.html
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by:mrjoltcola
ID: 24061065
FYI I have disabled multi-line comments in my own compilers just for simplicity. I stick with the // and #

But its not too difficult, it helps if you make use of lexer states. If I were you (unknown_) I would stick with single line comments and move on to properly finishing your compiler project. I'm just saying this because I and Infinity have an idea of where you are due to helping you with it in several areas (which we are happy to continue with), and I feel like you may be distracting yourself from the importance of building a proper grammar and code generator.

You can always add C comments later.

That said, its up to you, so if you don't agree, Infinity's link should help.

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by:Infinity08
ID: 24062164
Good point, mrjoltcola.
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