爲什麼YACC有這個警告？

我在我的大學有一個項目，用C語言製作一個迷你shell。解析命令行我使用的工具：lex和yacc。與YACC編譯時，我得到這些警告，但我不明白爲什麼。爲什麼YACC有這個警告？

文件parser.yacc：

%{ 
#include <stdio.h> 
void yyerror(char *s); 
extern int yylex(); 
%} 
%token NEWLINE PIPE AND OR AMPERSAND BLANK WORD IDENTIFIER GREAT GREAT_GREAT LESS ERR_GREAT ERR_GREAT_GREAT GREAT_AMP GREAT_GREAT_AMP SEMICOLON 
%start cmd_lists 
%% 
cmd_lists 
    : cmd_lists command 
    | 
    ; 
command 
    : pipeline io_list background NEWLINE 
    | NEWLINE 
    | error NEWLINE 
    ; 
pipeline 
    : pipeline PIPE cmd_args 
    | pipeline SEMICOLON cmd_args 
    | pipeline AND cmd_args 
    | pipeline OR cmd_args 
    | cmd_args 
    ; 
cmd_args 
    : WORD list_arg 
    ; 
list_arg 
    : list_arg WORD 
    ; 
io_list 
    : io_list io 
    ; 
background 
    : AMPERSAND 
    ; 
io 
    : GREAT WORD 
    | GREAT_GREAT WORD 
    | LESS WORD 
    | ERR_GREAT WORD 
    | ERR_GREAT_GREAT WORD 
    | GREAT_AMP WORD 
    | GREAT_GREAT_AMP WORD 
    ; 
%% 
void yyerror(char *s){ 
    fprintf(stderr,"yyerror : erreur : %s.\n",s); 
}

而且警告：

parser.yacc: warning: 6 nonterminals useless in grammar[-Wother] 
parser.yacc: warning: 17 rules useless in grammar [-Wother] 
parser.yacc:13.10-17: warning: nonterminal useless in grammar: : pipeline [-Wother] 
command: pipeline io_list background NEWLINE | NEWLINE | error NEWLINE; 
     ^^^^^^^^ 
parser.yacc:14.25-32: awarning: nonterminal useless in grammar: : cmd_args [-Wother] 
pipeline: pipeline PIPE cmd_args | pipeline SEMICOLON cmd_args | pipeline AND cmd_args | pipeline OR cmd_args | cmd_args; 
        ^^^^^^^^ 
parser.yacc:15.16-23:warning: nonterminal useless in grammar: : list_arg [-Wother] 
cmd_args: WORD list_arg; 
      ^^^^^^^^ 
parser.yacc:13.19-25: warning: nonterminal useless in grammar: : io_list [-Wother] 
command: pipeline io_list background NEWLINE | NEWLINE | error NEWLINE; 
       ^^^^^^^ 
parser.yacc:13.27-36: warning: nonterminal useless in grammar: : background [-Wother] 
command: pipeline io_list background NEWLINE | NEWLINE | error NEWLINE; 
         ^^^^^^^^^^ 
parser.yacc:17.18-19: warning: nonterminal useless in grammar: : io [-Wother] 
io_list: io_list io; 
       ^^ 
parser.yacc:13.10-44: warning: nonterminal useless in grammar:[-Wother] 
command: pipeline io_list background NEWLINE | NEWLINE | error NEWLINE; 
     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 
parser.yacc:14.11-32: warning: nonterminal useless in grammar: [-Wother] 
pipeline: pipeline PIPE cmd_args | pipeline SEMICOLON cmd_args | pipeline AND cmd_args | pipeline OR cmd_args | cmd_args; 
     ^^^^^^^^^^^^^^^^^^^^^^ 
parser.yacc:14.36-62: warning: nonterminal useless in grammar: [-Wother] 
pipeline: pipeline PIPE cmd_args | pipeline SEMICOLON cmd_args | pipeline AND cmd_args | pipeline OR cmd_args | cmd_args; 
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^ 
parser.yacc:14.66-86:warning: nonterminal useless in grammar:[-Wother] 
pipeline: pipeline PIPE cmd_args | pipeline SEMICOLON cmd_args | pipeline AND cmd_args | pipeline OR cmd_args | cmd_args; 
                   ^^^^^^^^^^^^^^^^^^^^^ 
parser.yacc:14.90-109: warning: nonterminal useless in grammar: [-Wother] 
pipeline: pipeline PIPE cmd_args | pipeline SEMICOLON cmd_args | pipeline AND cmd_args | pipeline OR cmd_args | cmd_args; 
                         ^^^^^^^^^^^^^^^^^^^^ 
parser.yacc:14.113-120: warning: nonterminal useless in grammar:[-Wother] 
pipeline: pipeline PIPE cmd_args | pipeline SEMICOLON cmd_args | pipeline AND cmd_args | pipeline OR cmd_args | cmd_args; 
                              ^^^^^^^^ 
parser.yacc:15.11-23: warning: warning: nonterminal useless in grammar:[-Wother] 
cmd_args: WORD list_arg; 
     ^^^^^^^^^^^^^ 
parser.yacc:16.11-23: warning: warning: nonterminal useless in grammar: [-Wother] 
list_arg: list_arg WORD ; 
     ^^^^^^^^^^^^^ 
parser.yacc:17.10-19: warning: nonterminal useless in grammar:[-Wother] 
io_list: io_list io; 
     ^^^^^^^^^^ 
parser.yacc:18.13-21:warning: nonterminal useless in grammar:[-Wother] 
background: AMPERSAND; 
     ^^^^^^^^^ 
parser.yacc:19.5-14: warning: nonterminal useless in grammar:[-Wother] 
io: GREAT WORD| GREAT_GREAT WORD| LESS WORD| ERR_GREAT WORD| ERR_GREAT_GREAT WORD| GREAT_AMP WORD| GREAT_GREAT_AMP WORD; 
^^^^^^^^^^ 
parser.yacc:19.17-32: warning: nonterminal useless in grammar:[-Wother] 
io: GREAT WORD| GREAT_GREAT WORD| LESS WORD| ERR_GREAT WORD| ERR_GREAT_GREAT WORD| GREAT_AMP WORD| GREAT_GREAT_AMP WORD; 
      ^^^^^^^^^^^^^^^^ 
parser.yacc:19.35-43: warning: nonterminal useless in grammar: [-Wother] 
io: GREAT WORD| GREAT_GREAT WORD| LESS WORD| ERR_GREAT WORD| ERR_GREAT_GREAT WORD| GREAT_AMP WORD| GREAT_GREAT_AMP WORD; 
           ^^^^^^^^^ 
parser.yacc:19.46-59: warning: nonterminal useless in grammar:[-Wother] 
io: GREAT WORD| GREAT_GREAT WORD| LESS WORD| ERR_GREAT WORD| ERR_GREAT_GREAT WORD| GREAT_AMP WORD| GREAT_GREAT_AMP WORD; 
              ^^^^^^^^^^^^^^ 
parser.yacc:19.62-81: warning: nonterminal useless in grammar: [-Wother] 
io: GREAT WORD| GREAT_GREAT WORD| LESS WORD| ERR_GREAT WORD| ERR_GREAT_GREAT WORD| GREAT_AMP WORD| GREAT_GREAT_AMP WORD; 
                  ^^^^^^^^^^^^^^^^^^^^ 
parser.yacc:19.84-97:warning: nonterminal useless in grammar:[-Wother] 
io: GREAT WORD| GREAT_GREAT WORD| LESS WORD| ERR_GREAT WORD| ERR_GREAT_GREAT WORD| GREAT_AMP WORD| GREAT_GREAT_AMP WORD; 
                       ^^^^^^^^^^^^^^ 
parser.yacc:19.100-119: warning: nonterminal useless in grammar:[-Wother] 
io: GREAT WORD| GREAT_GREAT WORD| LESS WORD| ERR_GREAT WORD| ERR_GREAT_GREAT WORD| GREAT_AMP WORD| GREAT_GREAT_AMP WORD;

我在YACC是新的。謝謝你的幫助。

來源

2016-09-29 Oneill

執行'bison'？，'yacc'？時，對於我們來說就是這樣：「LANG = C bison options bla bla bla」。寫'LANG = C'，讓野牛認爲系統語言環境是英語，給你英語警告。 –

你能否用C語言環境（'LC_ALL = C yacc parser.yacc'）調用'yacc'或'bison'？這樣，警告信息將以英文顯示，更多人知道發生了什麼。（對於那些看不懂的人：基本上每一個生產和非終端都被標記爲「未使用」）。 – 2016-09-29 08:35:02

你好，它已被編輯。 – Oneill

我已經改變了我parser.y文件，它的確定：

%{ 
#include <stdio.h> 
void yyerror(char *s); 
extern int yylex(); 
%} 
%token NEWLINE PIPE AND OR AMPERSAND BLANK WORD IDENTIFIER GREAT GREAT_GREAT LESS ERR_GREAT ERR_GREAT_GREAT GREAT_AMP GREAT_GREAT_AMP SEMICOLON 
%start cmd_lists 
%% 
cmd_lists: cmd_lists command | ; 
command: pipeline io_list background NEWLINE | NEWLINE | error NEWLINE; 
pipeline: pipeline PIPE cmd_args | pipeline SEMICOLON cmd_args | pipeline AND cmd_args | pipeline OR cmd_args | cmd_args; 
cmd_args: WORD list_arg; 
list_arg: list_arg WORD | /*empty*/; 
io_list: io_list io| /*empty*/ ; 
background: AMPERSAND | /*empty*/ ; 
io: GREAT WORD | GREAT_GREAT WORD | LESS WORD | ERR_GREAT WORD | ERR_GREAT_GREAT WORD | GREAT_AMP WORD | GREAT_GREAT_AMP WORD; 
%% 

void yyerror(char *s){ 
    fprintf(stderr,"yyerror : erreur : %s.\n",s); 
}

謝謝。

來源

2016-09-29 10:30:32 Oneill

爲什麼YACC有這個警告？

回答

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