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| | #REDIRECT [[ist:The Flex Lexical Analyzer]] |
| == Basic Concepts ==
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| * Definitions
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| * Rules, actions
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| * Code
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| * States and sub-automata
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| == Structure of a Flex Specification ==
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| == How to Debug a Flex Specification ==
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| There are various flags and variables to activate the debug functionality in Flex (there is no need to insert useless code such as printfs or similar).
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| The debug option will activate code for debugging as will the call to the <tt>set_debug</tt> method (see the scanner header file in Compact for an example).
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| In the CompactScanner.l file:
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| %option debug
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| This flag suffices when developing in C. When using C++ scanners ('''%option c++'''), even though the above flag still generates debug code, it's still necessary to tell the scanner to actually output debug information. This can be done by calling the '''set_debug''' method with a non-zero argument (this can be done conveniently at the start of the rules section in a Flex specification file -- note how the action is indented from the left and without any rule):
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| %%
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| { set_debug(1); }
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| Also, the YYDEBUG environment variable will activate the debug messages '''both''' in Flex and YACC (allowing simultaneous debugging of token recognition by the scanner and corresponding use by the parser). In the command line (syntax may vary, depending on the actual environment definition circumstances):
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| export YYDEBUG=1
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| == Examples ==
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| * [[Extracting HREF attributes from HTML files]]
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| == Exercises ==
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| * [[The Flex Lexical Analyzer/Exercise 1|Exercise 1]]
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| * [[The Flex Lexical Analyzer/Exercise 2|Exercise 2]]
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| * [[The Flex Lexical Analyzer/Exercise 3|Exercise 3]]
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| [[category:Compilers]]
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| [[category:Teaching]]
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