嗨，我是lex / yacc的新手，我正在练习实现一个解析器来定义一组变量，比如int x，y，z;双a，b; char c . 我需要为变量分配一个常量值，并管理字符常量以及打印所有变量及其类型和值 . 我有一些在线编码，我编辑但总是遇到错误 . 如果有人可以帮助我 .
lex代码（calc.l）
%{
#include "y.tab.h"
%}
%%
"print" {return print;}
"exit" {return exit_command;}
[a-zA-Z] {yylval.id = yytext[0]; return identifier;}
[0-9]+ {yylval.num = atoi(yytext); return number;}
[a-zA-Z] {yylval.const = yytext[0]; return character;}
[0-9]*\.[0-9]+ {yylval.num = atoi(yytext); return decimal;}
[ \t\n] ;
[-+=;] {return yytext[0];}
. {ECHO; yyerror ("unexpected character");}
%%
int yywrap (void) {return 1;}
yacc code(calc.y)
%{
void yyerror (char *s);
#include <stdio.h> /* C declarations used in actions */
#include <stdlib.h>
int symbols[52];
int symbolVal(char symbol);
void updateSymbolVal(char symbol, int val);
void updateSymbolValD(char symbol, double dval);
void updateSymbolValC(char symbol, char cval);
%}
%union {int num; char id;double deci;char const;} /* Yacc definitions */
%start line
%token print
%token exit_command
%token <num> number
%token <id> identifier
%token <deci> decimal
%token <const> character
%type <num> line exp term
%type <id> assignment
%%
/* descriptions of expected inputs corresponding actions (in C) */
line : assignment ';' {;}
| exit_command ';' {exit(EXIT_SUCCESS);}
| print exp ';' {printf("Printing %d\n", $2);}
| line assignment ';' {;}
| line print exp ';' {printf("Printing %d\n", $3);}
| line exit_command ';' {exit(EXIT_SUCCESS);}
;
assignment : identifier '=' exp { updateSymbolVal($1,$3); }
;
exp : term {$$ = $1;}
;
term : number {$$ = $1;}
| character {$$ = $1;}
| decimal {$$ = $1;}
| identifier {$$ = symbolVal($1);}
;
%% /* C code */
int computeSymbolIndex(char token)
{
int idx = -1;
if(islower(token)) {
idx = token - 'a' + 26;
} else if(isupper(token)) {
idx = token - 'A';
}
return idx;
}
/* returns the value of a given symbol */
int symbolVal(char symbol)
{
int bucket = computeSymbolIndex(symbol);
return symbols[bucket];
}
/* updates the value of a given integer symbol */
void updateSymbolVal(char symbol, int val)
{
int bucket = computeSymbolIndex(symbol);
symbols[bucket] = val;
}
/* updates the value of a given double symbol */
void updateSymbolVal(char symbol, double dval)
{
int bucket = computeSymbolIndex(symbol);
symbols[bucket] = dval;
}
/* updates the value of a given character symbol */
void updateSymbolVal(char symbol, char cval)
{
int bucket = computeSymbolIndex(symbol);
symbols[bucket] = cval;
}
int main (void) {
/* init symbol table */
int i;
for(i=0; i<52; i++) {
symbols[i] = 0;
}
return yyparse ( );
}
void yyerror (char *s) {fprintf (stderr, "%s\n", s);}
它总是给我错误“"calc.l"，第9行：警告，规则无法匹配" which is this line of code " [a-zA-Z] {yylval.const = yytext[0]; return character;}"
我已将我的lex和yacc代码更改为下面的代码并遇到了另一个错误 . 我希望有人可以帮助我理解错误以及如何运行代码 . 我在线搜索错误的含义但是没有得到理解 .
**Lex codes**
calc.l
%{
#include "y.tab.h"
%}
%%
"print" {return print;}
"exit" {return exit_command;}
[a-zA-Z] {yylval.id = yytext[0]; return identifier;}
[0-9]+ {yylval.num = atoi(yytext); return number;}
[\'.\'] {yylval.const = yytext[0]; return character;}
[0-9]*\.[0-9]+ {yylval.deci = atof(yytext); return decimal;}
[ \t\n] ;
[=;] {return yytext[0];}
. {ECHO; yyerror ("unexpected character");}
%%
int yywrap (void) {return 1;}
**yacc codes**
**calc.y**
%{
void yyerror (char *s);
#include <stdio.h> /* C declarations used in actions */
#include <stdlib.h>
int symbols[52];
int symbolVal(char symbol);
void updateSymbolVal(char symbol, int val);
void updateSymbolValD(char symbol, double dval);
void updateSymbolValC(char symbol, char cval);
%}
%union {int num; char id;double deci;char const;} /* Yacc definitions */
%start line
%token print
%token exit_command
%token <num> number
%token <id> identifier
%token <deci> decimal
%token <const> character
%type <id> assignment
%type <id> charact_assign
%type <id> double_assign
%type <num> exp
%type <const> char_con
%type <deci> real_val
%%
/* descriptions of expected inputs corresponding actions (in C) */
line : assignment ';' {;}
| charact_assign ';' {;}
| double_assign ';' {;}
| exit_command ';' {exit(EXIT_SUCCESS);}
| print assignment ';' {printf("Printing %d\n", $2);}
| line assignment ';' {;}
| line charact_assign ';' {;}
| line double_assign ';' {;}
| line print assignment ';' {printf("Printing %d\n", $3);}
| line exit_command ';' {exit(EXIT_SUCCESS);}
;
assignment : identifier '=' exp { updateSymbolVal($1,$3); }
;
exp : number {$$ = $1;}
;
charact_assign: identifier '=' char_con { updateSymbolVal($1,$3); }
;
char_con : character {$$ = $1;}
;
double_assign: identifier '=' real_val { updateSymbolVal($1,$3); }
;
real_val : decimal {$$ = $1;}
;
%% /* C code */
int computeSymbolIndex(char token)
{
int idx = -1;
if(islower(token)) {
idx = token - 'a' + 26;
} else if(isupper(token)) {
idx = token - 'A';
}
return idx;
}
/* returns the value of a given symbol */
int symbolVal(char symbol)
{
int bucket = computeSymbolIndex(symbol);
return symbols[bucket];
}
/* updates the value of a given integer symbol */
void updateSymbolVal(char symbol, int val)
{
int bucket = computeSymbolIndex(symbol);
symbols[bucket] = val;
}
/* updates the value of a given double symbol */
void updateSymbolVal(char symbol, double dval)
{
int bucket = computeSymbolIndex(symbol);
symbols[bucket] = dval;
}
/* updates the value of a given character symbol */
void updateSymbolVal(char symbol, char cval)
{
int bucket = computeSymbolIndex(symbol);
symbols[bucket] = cval;
}
int main (void) {
/* init symbol table */
int i;
for(i=0; i<52; i++) {
symbols[i] = 0;
}
return yyparse ( );
}
void yyerror (char *s) {fprintf (stderr, "%s\n", s);}
**`Below are the errors i am running into:`**
"calc.y", line 12: unrecognized '%' directive
"calc.y", line 14: unrecognized '%' directive
"calc.y", line 15: unrecognized '%' directive
"calc.y", line 16: unrecognized '%' directive
"calc.y", line 17: unrecognized '%' directive
"calc.y", line 18: unrecognized '%' directive
"calc.y", line 19: unrecognized '%' directive
"calc.y", line 20: unrecognized '%' directive
"calc.y", line 21: unrecognized '%' directive
"calc.y", line 22: unrecognized '%' directive
"calc.y", line 23: unrecognized '%' directive
"calc.y", line 24: unrecognized '%' directive
"calc.y", line 25: unrecognized '%' directive
"calc.y", line 30: unrecognized rule
"calc.y", line 30: unrecognized rule
"calc.y", line 30: unrecognized rule
"calc.y", line 34: unrecognized rule
"calc.y", line 35: unrecognized rule
"calc.y", line 36: unrecognized rule
"calc.y", line 37: unrecognized rule
"calc.y", line 38: unrecognized rule
"calc.y", line 39: unrecognized rule
"calc.y", line 40: unrecognized rule
"calc.y", line 41: unrecognized rule
"calc.y", line 42: unrecognized rule
1 回答
你有两次相同的模式：
因此，匹配
a-zA-Z的任何内容都将与第一个匹配，并且没有任何内容与第二个匹配 .如果它没有使用't clear: a lex/flex lexer considers the rules in order, so the first rule that matches an input is the one that'（即使它们匹配，如果较早的模式匹配，则不考虑后面的模式） . 这就是为什么（例如）你总是将
.模式放在最后（假设你使用它，但你通常这样做） - 因为它会匹配任何东西，所以它后面没有任何模式可以匹配任何东西 .