Thread: Lexical convention from Dennis Ritchie's manual

  1. #1
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    Jan 2012

    Lexical convention from Dennis Ritchie's manual


    I have been confused by this statement in the Dennis Ritchie's manual:

    "If the input stream has been parsed into tokens up to a given character, the next token is taken to include the longest
    string of characters which could possibly constitute a token."

    What does this mean? It is under the Lexical Convention section of the manual.


  2. #2
    C++ Witch laserlight's Avatar
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    Oct 2003
    We say that the matching is greedy. For example, given the expression a+++b, we break it into the tokens a, ++, + and b rather than a, +, ++ and b.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  3. #3
    Officially An Architect brewbuck's Avatar
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    Mar 2007
    Portland, OR
    To extend what laserlight said, it means that if more than one match is possible for the next sequence of characters, then use the longest one.

    The rule is actually rather critical, as it causes the sequence of characters 'abc' to be parsed as the single identifier 'abc', instead of the identifier 'a' followed by identifier 'b' followed by identifier 'c'.
    	if (a) do { f( b); } while(1);
    	else   do { f(!b); } while(1);

  4. #4
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    Jan 2012
    Thank you laserlight and brewbuck for your responses. That answers my question.

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