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blogTitle:'利用flex & bison (lex & yacc)创建可重入(线程安全)的词法分析和语法解析器',
blogAbstract:'利用flex & bison (lex & yacc)创建可重入(线程安全)的词法分析和语法解析器利用flex & bison (lex & yacc)创建可重入(线程安全)的词法分析和语法解析器希望读者能有lex yacc基础。来自：/?p=29
使用flex(lex)和bison(yacc)可以非常方便的创建词法分析和语法分析器,典型的这类程序都是使用一些全局变量进行信息的传递,这也是程序默认的方式，比如：flex解析到一个string,可以通过yylval传递给再就是flex和bison默认是通过一些全局变量来保存解析的status信息。简单点说，flex和bison默认创建的词法分析和语法分析的C代码都不是线程安全的，都是不可重入的。',
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推荐过这篇日志的人：
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{list wl as x}{/list}ubuntu下bison编写语法分析器的问题用flex和bison编写语法分析器，但是有一行提示语法错误，涉及到“REALNUM”和“INTEGER”的产生式都会报错，求解答。测试内容为:main()
ubuntu下bison编写语法分析器的问题
用flex和bison编写语法分析器，但是有一行提示语法错误，涉及到“REALNUM”和“INTEGER”的产生式都会报错，求解答。
测试内容为:
此时能通过，但是测试内容为
就会报第5行第6行语法错误。求解。
相关代码如下：
flex.l中：
IDENTIFIER[a-zA-Z_$][a-zA-Z0-9_$]*
INTEGER ^-?[0-9]+$
REALNUM ^(-?[0-9]+)(.[0-9]+)?$
{IDENTIFIER}
{ids++; yylval.id=(char*)strdup(yytext);
return IDENTIFIER;}
yylval.interval = atoi(yytext);
return INTEGER;}
{reals++;yylval.realval = atof(yytext);
return REALNUM;}
{WHITESPACE}
{lineno++;}
syntax.y中
MAIN '(' ')' SBLOCK
{printf("(%d)t program -&MAIN() SBLOCKn",linenum++);}
'{' DECLS STMTS '}'
{printf("(%d)t SBLOCK -& { DECLS STMTS }n",linenum++);}
DECLS DECL
{printf("(%d)tDECLS -& DECLS DECLn",linenum++);}
{printf("(%d)tDECLS -& en",linenum++);}
INT IDENTIFIER ';'
{printf("(%d)tDECL -& INT %sn",linenum++,$2);}
|REAL IDENTIFIER ';'
{printf("(%d)tDECL -& REAL %sn",linenum++,$2);}
STMTS STMT
{printf("(%d)tSTMTS -& STMTS STMTn",linenum++);}
{printf("(%d)tSTMTS -& en",linenum++);}
IDENTIFIER ASSGNOP BEXP ';'
{printf("(%d)t STMT -& %s = BEXPn",linenum++,$1);}
|IF '(' BEXP ')' STMT %prec IF_THEN
{printf("(%d)t STMT -& IF ( BEXP ) STMTn",linenum++);}
|IF '(' BEXP ')' STMT ELSE STMT
{printf("(%d)t STMT -& IF ( BEXP ) STMT ELSE STMTn",linenum++);}
|WHILE '(' BEXP ')' STMT
{printf("(%d)t STMT -& WHILE ( BEXP ) SBLOCKn",linenum++);}
|DO STMT WHILE '(' BEXP ')' ';'
{printf("(%d)t STMT -& DO SBLOCK WHILE ( BEXP ) ;n",linenum++);}
BEXP OR JOIN
{printf("(%d)tBEXP -& BEXP || JOINn",linenum++);}
{printf("(%d)tBEXP -& JOIN n",linenum++);}
JOIN AND EQEXP
{printf("(%d)tJOIN -& JOIN && EQEXPn",linenum++);}
{printf("(%d)tJOIN -& EQEXPn",linenum++);}
EQEXP EQ REL
{printf("(%d)tEQEXP -& EQEXP == RELn",linenum++);}
|EQEXP NE REL
{printf("(%d)tEQEXP -& EQEXP != RELn",linenum++);}
{printf("(%d)tEQEXP -& RELn",linenum++);}
EXP GT EXP
{printf("(%d)tREL -& EXP & EXPn",linenum++);}
|EXP LT EXP
{printf("(%d)tREL -& EXP & EXPn",linenum++);}
|EXP GE EXP
{printf("(%d)tREL -& EXP &= EXPn",linenum++);}
|EXP LE EXP
{printf("(%d)tREL -& EXP &= EXPn",linenum++);}
{printf("(%d)tREL -& EXPn",linenum++);}
EXP '+' TERM
{printf("(%d)tEXP -& EXP + TERMn",linenum++);}
|EXP '-' TERM
{printf("(%d)tEXP -& EXP - TERMn",linenum++);}
{printf("(%d)tEXP -& TERMn",linenum++);}
TERM '*' UNARY
{printf("(%d)tTERM -& TERM * UNARYn",linenum++);}
|TERM '/' UNARY
{printf("(%d)tTERM -& TERM / UNARYn",linenum++);}
{printf("(%d)tTERM -& UNARYn",linenum++);}
{printf("(%d)tUNARY -& ! UNARYn",linenum++);}
//|'-' UNARY
{printf("(%d)tUNARY -& - UNARYn",linenum++);}
{printf("(%d)tUNARY -& FACTORn",linenum++);}
'(' BEXP ')'
{printf("(%d)tFACTOR -& ( BEXP )n",linenum++);}
{printf("(%d)tFACTOR -& %dn",linenum++,$1);}
{printf("(%d)tFACTOR -& %fn",linenum++,$1);}
|IDENTIFIER
{printf("(%d)tFACTOR -& %sn",linenum++,$1);}
{printf("(%d)tFACTOR -& truen",linenum++);}
{printf("(%d)tFACTOR -& falsen",linenum++);}
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