FAQ

From time to time, the flex maintainer receives certain questions. Rather than repeat answers to well-understood problems, we publish them here.

When was flex born?
How do I expand backslash-escape sequences in C-style quoted strings?
Why do flex scanners call fileno if it is not ANSI compatible?
Does flex support recursive pattern definitions?
How do I skip huge chunks of input (tens of megabytes) while using flex?
Flex is not matching my patterns in the same order that I defined them.
My actions are executing out of order or sometimes not at all.
How can I have multiple input sources feed into the same scanner at the same time?
Can I build nested parsers that work with the same input file?
How can I match text only at the end of a file?
How can I make REJECT cascade across start condition boundaries?
Why can’t I use fast or full tables with interactive mode?
How much faster is -F or -f than -C?
If I have a simple grammar can’t I just parse it with flex?
Why doesn’t yyrestart() set the start state back to INITIAL?
How can I match C-style comments?
The ’.’ isn’t working the way I expected.
Can I get the flex manual in another format?
Does there exist a "faster" NDFA->DFA algorithm?
How does flex compile the DFA so quickly?
How can I use more than 8192 rules?
How do I abandon a file in the middle of a scan and switch to a new file?
How do I execute code only during initialization (only before the first scan)?
How do I execute code at termination?
Where else can I find help?
Can I include comments in the "rules" section of the file?
I get an error about undefined yywrap().
How can I change the matching pattern at run time?
How can I expand macros in the input?
How can I build a two-pass scanner?
How do I match any string not matched in the preceding rules?
I am trying to port code from AT&T lex that uses yysptr and yysbuf.
Is there a way to make flex treat NULL like a regular character?
Whenever flex can not match the input it says "flex scanner jammed".
Why doesn’t flex have non-greedy operators like perl does?
Memory leak - 16386 bytes allocated by malloc.
How do I track the byte offset for lseek()?
25.1 How do I use my own I/O classes in a C++ scanner?
How do I skip as many chars as possible?
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Are certain equivalent patterns faster than others?
Is backing up a big deal?
Can I fake multi-byte character support?
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Can you discuss some flex internals?
unput() messes up yy_at_bol
The \| operator is not doing what I want
Why can’t flex understand this variable trailing context pattern?
The ^ operator isn’t working
Trailing context is getting confused with trailing optional patterns
Is flex GNU or not?
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I need to scan if-then-else blocks and while loops
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Is there a repository for flex scanners?
How can I conditionally compile or preprocess my flex input file?
Where can I find grammars for lex and yacc?
I get an end-of-buffer message for each character scanned.
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What is the difference between YYLEX_PARAM and YY_DECL?
Why do I get "conflicting types for yylex" error?
How do I access the values set in a Flex action from within a Bison action?

This document was generated on November 4, 2011 using texi2html 5.0.