【发布时间】：2019-07-13 21:33:12
【问题描述】：
程序旨在将值存储在符号表中，然后能够将它们打印出来，说明词性。进一步在解析器中被解析并声明更多，是否是一个句子等等。
我通过
创建可执行文件flex try1.l
bison -dy try1.y
gcc lex.yy.c y.tab.c -o try1.exe
在 cmd (WINDOWS) 中
当我在运行可执行文件时尝试声明任何值时，就会出现我的问题， 动词跑 它是这样的 粗体是输入
动词运行
运行
运行
语法错误
名词猫
猫
语法错误
运行
运行
语法错误
cat run
语法错误
我的想法：我不确定为什么我会从代码语法错误中得到这个错误。尽管在调试并尝试打印出存储的值之后，我认为链表肯定存在某种问题。因为似乎只有一个值存储在链表中并导致各种错误。当我试图打印出存储的 word_type 整数值以进行运行时，它会打印出正确的值 259，但会拒绝让我在符号表中定义任何其他单词。我颠倒了 print 语句的更改，现在它按前面所述工作。我再次认为 addword 方法存在问题，因为它没有正确添加，因此查找方法使程序崩溃。
Lexer 文件，这个例子取自 O'Reily 2nd edition on Lex And Yacc， 示例 1-5,1-6。 我正在尝试自己学习 Lex 和 Yacc 并重现此示例。
%{
/*
* We now build a lexical analyzer to be used by a higher-level parser.
*/
#include <stdlib.h>
#include <string.h>
#include "ytab.h" /* token codes from the parser */
#define LOOKUP 0 /* default - not a defined word type. */
int state;
%}
/*
* Example from page 9 Word recognizer with a symbol table. PART 2 of Lexer
*/
%%
\n { state = LOOKUP; } /* end of line, return to default state */
\.\n { state = LOOKUP;
return 0; /* end of sentence */
}
/* whenever a line starts with a reserved part of speech name */
/* start defining words of that type */
^verb { state = VERB; }
^adj { state = ADJ; }
^adv { state = ADV; }
^noun { state = NOUN; }
^prep { state = PREP; }
^pron { state = PRON; }
^conj { state = CONJ; }
[a-zA-Z]+ {
if(state != LOOKUP) {
add_word(state, yytext);
} else {
switch(lookup_word(yytext)) {
case VERB:
return(VERB);
case ADJECTIVE:
return(ADJECTIVE);
case ADVERB:
return(ADVERB);
case NOUN:
return(NOUN);
case PREPOSITION:
return(PREPOSITION);
case PRONOUN:
return(PRONOUN);
case CONJUNCTION:
return(CONJUNCTION);
default:
printf("%s: don't recognize\n", yytext);
/* don't return, just ignore it */
}
}
}
. ;
%%
int yywrap()
{
return 1;
}
/* define a linked list of words and types */
struct word {
char *word_name;
int word_type;
struct word *next;
};
struct word *word_list; /* first element in word list */
extern void *malloc() ;
int
add_word(int type, char *word)
{
struct word *wp;
if(lookup_word(word) != LOOKUP) {
printf("!!! warning: word %s already defined \n", word);
return 0;
}
/* word not there, allocate a new entry and link it on the list */
wp = (struct word *) malloc(sizeof(struct word));
wp->next = word_list;
/* have to copy the word itself as well */
wp->word_name = (char *) malloc(strlen(word)+1);
strcpy(wp->word_name, word);
wp->word_type = type;
word_list = wp;
return 1; /* it worked */
}
int
lookup_word(char *word)
{
struct word *wp = word_list;
/* search down the list looking for the word */
for(; wp; wp = wp->next) {
if(strcmp(wp->word_name, word) == 0)
return wp->word_type;
}
return LOOKUP; /* not found */
}
yacc 文件，
%{
/*
* A lexer for the basic grammar to use for recognizing English sentences.
*/
#include <stdio.h>
%}
%token NOUN PRONOUN VERB ADVERB ADJECTIVE PREPOSITION CONJUNCTION
%%
sentence: subject VERB object{ printf("Sentence is valid.\n"); }
;
subject: NOUN
| PRONOUN
;
object: NOUN
;
%%
extern FILE *yyin;
main()
{
do
{
yyparse();
}
while (!feof(yyin));
}
yyerror(s)
char *s;
{
fprintf(stderr, "%s\n", s);
}
头文件，必须为某些值创建 2 个版本，不知道为什么，但代码有问题每个人只有一个。
# define NOUN 257
# define PRON 258
# define VERB 259
# define ADVERB 260
# define ADJECTIVE 261
# define PREPOSITION 262
# define CONJUNCTION 263
# define ADV 260
# define ADJ 261
# define PREP 262
# define CONJ 263
# define PRONOUN 258
【问题讨论】：
标签： c windows debugging bison flex-lexer