我有一个用于c语言的词法分析器和解析器，但我不明白为什么
给定输入存在语法错误
这是词法分析器
%option yylineno
%{
#include "y.tab.h"
#include <stdio.h>
%}
DIGIT [0-9]+
ID [a-zA-Z][a-zA-Z0-9_]*
%%
"/*"([^\*\n\r]*) {printf("Non-terminated comments, Line Number: %d\n",yylineno);}
[/*]+[/*][a-zA-Z0-9]*[*/]+[*/] {printf("<Comment, %s, %d>\n", yytext,yylineno);}
"if" {printf("<keyword, %s, %d>\n", yytext,yylineno); yylval = *yytext; return IF ;}
"else" {printf("<keyword, %s, %d>\n", yytext,yylineno );yylval = *yytext; return ELSE;}
"for" {printf("<keyword, %s, %d>\n", yytext,yylineno );yylval = *yytext; return FOR;}
"begin" {printf("<keyword, %s, %d>\n", yytext,yylineno ); }
"end" {printf("<keyword, %s, %d>\n", yytext,yylineno ); }
"procedure" {printf("<keyword, %s, %d>\n", yytext,yylineno ); }
"function" {printf("<keyword, %s, %d>\n", yytext,yylineno ); }
"void" {printf("<keyword, %s, %d>\n", yytext,yylineno );yylval = *yytext; return VOID;}
"main" {printf("<keyword, %s, %d>\n", yytext,yylineno ); }
"int" {printf("<keyword, %s, %d>\n", yytext,yylineno );yylval = *yytext; return INT;}
"float" {printf("<keyword, %s, %d>\n", yytext,yylineno );yylval = *yytext; return FLOAT;}
"printf" {printf("<keyword, %s, %d>\n", yytext,yylineno ); }
"while" {printf("<keyword, %s, %d>\n", yytext,yylineno );yylval = *yytext; return WHILE;}
"char" {printf("<keyword, %s, %d>\n", yytext,yylineno );yylval = *yytext; return CHAR;}
"switch" {printf("<keyword, %s, %d>\n", yytext,yylineno );yylval = *yytext; return SWITCH;}
"case" {printf("<keyword, %s, %d>\n", yytext,yylineno );yylval = *yytext; return CASE;}
"default" {printf("<keyword, %s, %d>\n", yytext,yylineno );yylval = *yytext; return DEFAULT;}
"break" {printf("<keyword, %s, %d>\n", yytext,yylineno );yylval = *yytext; return BREAK;}
"do" {printf("<keyword, %s, %d>\n", yytext,yylineno );yylval = *yytext; return DO;}
"continue" {printf("<keyword, %s, %d>\n", yytext,yylineno ); yylval = *yytext;return CONTINUE;}
"return" {printf("<keyword, %s, %d>\n", yytext,yylineno ); yylval = *yytext;return RETURN;}
"+" {printf("<operator, %s, %d>\n", yytext,yylineno );yylval = *yytext;return ADD;}
"-" {printf("<operator, %s, %d>\n", yytext,yylineno );yylval = *yytext;return SUBTRACT;}
"*" {printf("<operator, %s, %d>\n", yytext,yylineno );yylval = *yytext;return MULTIPLY;}
"/" {printf("<operator, %s, %d>\n", yytext,yylineno );yylval = *yytext;return DIVIDE;}
"<" {printf("<operator, %s, %d>\n", yytext,yylineno );yylval = *yytext;return LESSTHAN;}
">" {printf("<operator, %s, %d>\n", yytext,yylineno );yylval = *yytext;return GREATERTHAN;}
"++" {printf("<operator, %s, %d>\n", yytext,yylineno );yylval = *yytext;return INCREMENT;}
"--" {printf("<operator, %s, %d>\n", yytext,yylineno );yylval = *yytext;return DECREMENT;}
"=" {printf("<operator, %s, %d>\n", yytext,yylineno );yylval = *yytext;return ASSIGN;}
"==" {printf("<operator, %s, %d>\n", yytext,yylineno );yylval = *yytext;return ISEQUALTO;}
">=" {printf("<operator, %s, %d>\n", yytext,yylineno );yylval = *yytext;return GREATERTHANEQUALTO;}
"<=" {printf("<operator, %s, %d>\n", yytext,yylineno );yylval = *yytext;return LESSTHANEQUALTO;}
"%" {printf("<operator, %s, %d>\n", yytext,yylineno );yylval = *yytext;return MODULUS;}
"!=" {printf("<operator, %s, %d>\n", yytext,yylineno );yylval = *yytext;return ISNOTEQUALTO;}
"+=" {printf("<operator, %s, %d>\n", yytext,yylineno );yylval = *yytext;return ADDANDASSIGN;}
"-=" {printf("<operator, %s, %d>\n", yytext,yylineno );yylval = *yytext;return SUBTRACTANDASSIGN;}
"*=" {printf("<operator, %s, %d>\n", yytext,yylineno );yylval = *yytext;return MULTIPLYANDASSIGN;}
"/=" {printf("<operator, %s, %d>\n", yytext,yylineno );yylval = *yytext;return DIVIDEANDASSIGN;}
"%=" {printf("<operator, %s, %d>\n", yytext,yylineno );yylval = *yytext;return MODULUSANDASSIGN;}
"?:" {printf("<operator, %s, %d>\n", yytext,yylineno );yylval = *yytext;return CONDITIONALOPERATOR;}
"," {printf("<Comma, %s, %d>\n", yytext,yylineno );yylval = *yytext;return COMMA;}
";" {printf("<Terminator, %s, %d>\n", yytext,yylineno );yylval = *yytext;return ENDOFSTATEMENT;}
":" {printf("<Colon, %s, %d>\n", yytext,yylineno );yylval = *yytext;return COLON;}
"(" {printf("<OpeningRoundBracket, %s, %d>\n", yytext,yylineno );return OPENINGROUND;}
")" {printf("<ClosingRoundBracket, %s, %d>\n", yytext,yylineno );return CLOSINGROUND;}
"{" {printf("<OpeningCurlyBracket, %s, %d>\n", yytext,yylineno );yylval = *yytext;return OPENINGBRACE;}
"}" {printf("<ClosingCurlyBracket, %s, %d>\n", yytext,yylineno );yylval = *yytext;return CLOSINGBRACE;}
"[" {printf("<OpeningSquareBracket, %s, %d>\n", yytext,yylineno );yylval = *yytext;return OPENINGSQUARE;}
"]" {printf("<ClosingSquareBracket, %s, %d>\n", yytext,yylineno );yylval = *yytext;return CLOSINGSQUARE;}
[*]+{ID}+ {printf("<Pointer, %s, %d>\n", yytext,yylineno);}
{DIGIT}+ {printf("<INTEGER, %s, %d>\n", yytext,yylineno);yylval = atoi(yytext);return INTEGER;}
{DIGIT}+"."{DIGIT}* {printf("<FLOAT, %s, %d>\n", yytext,yylineno);yylval = atoi(yytext);return INTEGER ;}
["]+{ID}*[ ]*[:]*[;]*[(]*[)]*{ID}*["]+ {printf("<STRING, %s, %d>\n", yytext,yylineno);yylval = atoi(yytext);return REAL ;}
[']{ID}['] {printf("<CHAR, %s, %d>\n", yytext,yylineno);yylval = *yytext;return CHARACTER ;}
[']{ID}{ID}+['] {printf("CHAR constant too long: %s, Line Number: %d\n", yytext,yylineno);}
{ID}+ {printf("<Identifier, %s, %d>\n", yytext,yylineno ); yylval = *yytext; return IDENTIFIER ;}
" " ;{printf("Space");}/* eat up whitespace */
"\t" ;/* eat up whitespace */
"\n" ;/* eat up whitespace */
"#" {printf("Undefined Symbol: %s, Line Number: %d>\n", yytext,yylineno );}
"~" {printf("Undefined Symbol: %s, Line Number: %d>\n", yytext,yylineno );}
. printf( "Undefined Symbol: %s, %d\n",yytext,yylineno );
%%
int yywrap(){
return 1;
}
解析器.y文件
%{
#include <stdio.h>
#include <stdlib.h>
void yyerror();
FILE *f;
%}
%token IF
%token ELSE
%token FOR
%token VOID
%token INT
%token FLOAT
%token WHILE
%token CHAR
%token SWITCH
%token CASE
%token DEFAULT
%token BREAK
%token DO
%token CONTINUE
%token RETURN
%token ADD
%token SUBTRACT
%token MULTIPLY
%token DIVIDE
%token MODULUS
%token LESSTHAN
%token GREATERTHAN
%token INCREMENT
%token DECREMENT
%token ASSIGN
%token ISEQUALTO
%token GREATERTHANEQUALTO
%token LESSTHANEQUALTO
%token ISNOTEQUALTO
%token ADDANDASSIGN
%token SUBTRACTANDASSIGN
%token MULTIPLYANDASSIGN
%token DIVIDEANDASSIGN
%token MODULUSANDASSIGN
%token CONDITIONALOPERATOR
%token ENDOFSTATEMENT
%token COMMA
%token COLON
%token OPENINGROUND
%token CLOSINGROUND
%token OPENINGSQUARE
%token CLOSINGSQUARE
%token OPENINGBRACE
%token CLOSINGBRACE
%token INTEGER
%token REAL
%token CHARACTER
%token IDENTIFIER
%start TransitionUnit
%%
TransitionUnit : ExternalDeclaration TransitionUnit_a;
TransitionUnit_a : ExternalDeclaration TransitionUnit_a
| /* NULL */
;
ExternalDeclaration : FunctionDefinition
|Declaration ENDOFSTATEMENT
;
FunctionDefinition : TypeSpecifier Declarator FunctionDefinition_a
|Declarator FunctionDefinition_b
;
FunctionDefinition_a : DeclarationList CompoundStatement
|CompoundStatement;
FunctionDefinition_b : DeclarationList CompoundStatement
|CompoundStatement
;
TypeSpecifier : VOID
|CHAR
|INT
|FLOAT
;
Declarator : DirectDeclarator
| Pointer DirectDeclarator;
DirectDeclarator : IDENTIFIER DirectDeclarator_a;
DirectDeclarator_a : OPENINGROUND DirectDeclarator_b
|OPENINGSQUARE DirectDeclarator_c
|/* NULL */
;
DirectDeclarator_b : Declarator CLOSINGROUND DirectDeclarator_a
|ParameterList CLOSINGROUND DirectDeclarator_a
|CLOSINGROUND DirectDeclarator_a
;
DirectDeclarator_c : CLOSINGSQUARE DirectDeclarator_a
|INT CLOSINGSQUARE DirectDeclarator_a
;
Pointer : MULTIPLY Pointer_a
;
Pointer_a : Pointer
|/* NULL */
;
DeclarationList : Declaration ENDOFSTATEMENT DeclarationList_a
;
DeclarationList_a : Declaration ENDOFSTATEMENT DeclarationList_a
|/* NULL */
;
Declaration : TypeSpecifier Declaration_a;
Declaration_a : InitDeclaratorList
|/* NULL */
;
InitDeclaratorList : InitDeclarator InitDeclaratorList_a
;
InitDeclaratorList_a : COMMA InitDeclarator InitDeclaratorList_a
|/* NULL */
;
InitDeclarator : Declarator InitDeclarator_a
;
InitDeclarator_a : ASSIGN Initializer
|/* NULL */
;
Initializer : Constant
| OPENINGBRACE InitializerList Initializer_a
;
Initializer_a : CLOSINGBRACE
|COMMA CLOSINGBRACE
;
InitializerList : Initializer InitializerList_a
;
InitializerList_a : COMMA Initializer InitializerList_a
|/* NULL */
;
ParameterList : ParameterDeclaration ParameterList_a;
ParameterList_a : COMMA ParameterDeclaration ParameterList_a
|/* NULL */
;
ParameterDeclaration : TypeSpecifier ParameterDeclaration_a;
ParameterDeclaration_a : Declarator
|/* NULL */;
CompoundStatement : OPENINGBRACE CompoundStatement_a;
CompoundStatement_a : CLOSINGBRACE
|StatementList CLOSINGBRACE
|DeclarationList CompoundStatement_b
;
CompoundStatement_b : StatementList CLOSINGBRACE
|CLOSINGBRACE
;
StatementList : Statement StatementList_a;
StatementList_a : Statement StatementList_a
|/* NULL */
;
Statement : LabeledStatement
|CompoundStatement
|ExpressionStatement
|SelectionStatement
|IterationStatement
|JumpStatement;
LabeledStatement : CASE Constant COLON Statement
|DEFAULT COLON Statement;
ExpressionStatement : ENDOFSTATEMENT
|Expression ENDOFSTATEMENT
;
SelectionStatement : IF OPENINGROUND Expression CLOSINGROUND Statement SelectionStatement_a
|SWITCH OPENINGROUND Expression CLOSINGROUND Statement;
SelectionStatement_a : ELSE Statement
|/* NULL */
;
JumpStatement : CONTINUE ENDOFSTATEMENT
|BREAK ENDOFSTATEMENT
|RETURN JumpStatement_a
;
JumpStatement_a : Expression ENDOFSTATEMENT;
IterationStatement : WHILE OPENINGROUND Expression CLOSINGROUND Statement
|DO Statement WHILE OPENINGROUND Expression CLOSINGROUND ENDOFSTATEMENT
|FOR OPENINGROUND Expression ENDOFSTATEMENT Expression ENDOFSTATEMENT Expression CLOSINGROUND Statement
;
ConditionalExpression : EqualityExpression ConditionalExpression_a;
ConditionalExpression_a : CONDITIONALOPERATOR Expression COLON ConditionalExpression
|
;
Expression : AssignmentExpression Expression_a;
Expression_a : COMMA AssignmentExpression Expression_a
|
;
AssignmentExpression : ConditionalExpression
|UnaryExpression AssignmentOperator AssignmentExpression;
EqualityExpression : RelationalExpression EqualityExpression_a;
EqualityExpression_a : ISEQUALTO RelationalExpression EqualityExpression_a '\n'
|ISNOTEQUALTO RelationalExpression EqualityExpression_a
|
;
RelationalExpression : AdditiveExpression RelationalExpression_a;
RelationalExpression_a : LESSTHAN AdditiveExpression RelationalExpression_a '\n'
|GREATERTHAN AdditiveExpression RelationalExpression_a
|LESSTHANEQUALTO AdditiveExpression RelationalExpression_a
|GREATERTHANEQUALTO AdditiveExpression RelationalExpression_a
|
;
AdditiveExpression : MultiplicativeExpression AdditiveExpression_a;
AdditiveExpression_a : ADD MultiplicativeExpression AdditiveExpression_a '\n'
|SUBTRACT MultiplicativeExpression AdditiveExpression_a
|
;
MultiplicativeExpression : UnaryExpression MultiplicativeExpression_a;
MultiplicativeExpression_a : MULTIPLY UnaryExpression MultiplicativeExpression_a '\n'
| DIVIDE UnaryExpression MultiplicativeExpression_a
| MODULUS UnaryExpression MultiplicativeExpression_a
|
;
AssignmentOperator : ASSIGN
| ADDANDASSIGN
| SUBTRACTANDASSIGN
| MULTIPLYANDASSIGN
| DIVIDEANDASSIGN
| MODULUSANDASSIGN
;
Constant : INTEGER
| CHARACTER
| REAL
;
UnaryExpression : PostFixExpression
| INCREMENT UnaryExpression
| DECREMENT UnaryExpression
;
PostFixExpression : PrimaryExpression PostFixExpression_a;
PostFixExpression_a : OPENINGSQUARE Expression CLOSINGSQUARE PostFixExpression_a '\n'
| OPENINGROUND PostFixExpression_b
| INCREMENT PostFixExpression_a
| DECREMENT PostFixExpression_a
|
;
PostFixExpression_b : ArgumentExpressionList CLOSINGROUND PostFixExpression_a
| CLOSINGROUND PostFixExpression_a
;
ArgumentExpressionList : AdditiveExpression ArgumentExpressionList_a;
ArgumentExpressionList_a : COMMA AdditiveExpression ArgumentExpressionList_a '\n'
|
;
PrimaryExpression : IDENTIFIER { fprintf(f, "Got an %s",yylval);}
| Constant
;
%%
void yyerror(char *s){
extern int yylineno;
printf("%s at line no. %d",s,yylineno);
}
int main(){
extern FILE *yyin;
yyin = fopen("input.txt","r");
f = fopen("output.txt","w");
fprintf(f,"Adha Hogaya");
yyparse();
return 1;
}
要解析的输入文件
int i;
int a;
void main(){
}
代码解析正常，直到＆＃39;（＆＃39;之后显示为 语法错误。我不明白一些帮助会有什么问题 不胜感激
代码通过以下命令编译
flex 'filename'.l
bison -dy 'filename'.y
gcc lex.yy.c y.tab.c -o 'filename'.exe
答案 0 :(得分：1)
您的扫描仪会忽略＆＃34;关键字＆＃34; main（因为它不会返回任何内容）。
"main" {printf("<keyword, %s, %d>\n", yytext,yylineno ); }
我不清楚为什么你希望main成为关键字，因为你的语法似乎不允许名字不是标识符的函数。
真的，扫描仪定义中充满了问题，其中大部分与此问题无关。但是你真的应该看看一些示例扫描仪定义和（重新）阅读flex手册。首先，建议您使用单字符令牌（{而不是OPENINGBRACE），这样可以使您的扫描程序和解析器更具可读性。但是您需要仔细查看一些扫描仪模式，尤其是注释模式和字符串/字符文字模式。您的ID宏不是单个字符，因此在其他模式中使用{ID}+肯定是错误的（并导致出现弹出警告）。
flex和bison都提供调试跟踪功能，这比使用printf语句填充源代码要容易得多。如果您只是使用了这些痕迹，您会立即看到＆＃34;关键字＆＃34; main未发送给解析器。请参阅flex manual和bison manual的调试部分。
您的语法文件看起来像是在尝试编写适合LL（1）（递归下降）解析器的语法。这是完全没必要的 - bison / yacc是一个LALR（1）解析器生成器，它可以很好地处理左递归 - 并且使你的语法更不易读。考虑一下简单的区别：
Prototype: '(' ')'
| '(' ParameterList ')'
ParameterList
: ParameterDeclaration
| ParameterList ',' ParameterDeclaration;
ParameterDeclaration
: TypeSpecifier
| TypeSpecifier Declarator
最后，您需要修复语义值类型; yylval = *yytext很少有用。 （没有必要为没有语义值的令牌设置yylval。）默认的int类型不允许您将字符串（标识符或字符串文字）传递给扫描仪，它们会在可能很有用。