如何使用yacc生成c语言语法

分析器？

要使用 yacc 生成 C 语言的语法分析器，需要以下步骤：

1. 编写一个语法描述文件，也称为 .y 文件，用来定义语言的语法结构和相应的语义动作。

2. 使用 yacc 工具来将该语法描述文件编译生成相应的 C 语言代码。

3. 编译上一步中生成的 C 语言代码并运行，即可使用生成的语法分析器来解析相应的代码。

具体使用方法请参考 yacc 工具的使用手册或者相关教程。

相关问题

使用lex,yacc实现C语言的词法分析、语法分析，最后输出抽象语法树(AST),不要求typedef，#define复杂语法，给出完整详细的lex代码和yacc代码

本问题所需的代码较为复杂，无法在此处全部展示。以下是一个简化版本，供参考：

1. Lex代码：

%{
#include <stdio.h>
#include <stdlib.h>
#include "y.tab.h"
%}

%%

"int"           { return INT; }
"float"         { return FLOAT; }
"char"          { return CHAR; }
"double"        { return DOUBLE; }
"if"            { return IF; }
"else"          { return ELSE; }
"while"         { return WHILE; }
"for"           { return FOR; }
"do"            { return DO; }
"return"        { return RETURN; }
[0-9]+          { yylval.num = atoi(yytext); return NUM; }
[a-zA-Z_][a-zA-Z0-9_]*   { yylval.str = strdup(yytext); return ID; }
"=="            { return EQ; }
"!="            { return NE; }
">="            { return GE; }
"<="            { return LE; }
">"             { return GT; }
"<"             { return LT; }
"="             { return ASSGN; }
"+"             { return PLUS; }
"-"             { return MINUS; }
"*"             { return MULT; }
"/"             { return DIV; }
"%"             { return MOD; }
"("             { return LPAREN; }
")"             { return RPAREN; }
"{"             { return LBRACE; }
"}"             { return RBRACE; }
";"             { return SEMICOLON; }
","             { return COMMA; }
"["             { return LBRACKET; }
"]"             { return RBRACKET; }
"'"             { return SQUOTE; }
\"              { return DQUOTE; }
[ \t\n]         ; /* ignore white space */

.               { printf("Unknown token: %s\n", yytext); }
%%

int yywrap() {
    return 1;
}

2. Yacc代码：

%{
#include <stdio.h>
#include <stdlib.h>
#include "tree.h"
%}

%union {
    int num;
    char *str;
    Node *node;
}

%token <num> NUM
%token <str> ID
%token INT FLOAT CHAR DOUBLE IF ELSE WHILE FOR DO RETURN
%token EQ NE GE LE GT LT ASSGN PLUS MINUS MULT DIV MOD LPAREN RPAREN LBRACE RBRACE SEMICOLON COMMA LBRACKET RBRACKET SQUOTE DQUOTE

%type <node> program decl_list decl var_list var stmt_list stmt expr term factor

%start program

%%

program: decl_list {
    $$ = create_node(PROGRAM, $1, NULL, NULL);
}

decl_list: /* empty */ {
    $$ = NULL;
}
| decl_list decl {
    $$ = create_node(DECL_LIST, $1, $2, NULL);
}

decl: type var_list SEMICOLON {
    $$ = create_node(DECL, $1, $2, NULL);
}

type: INT {
    $$ = create_node(TYPE, "int", NULL, NULL);
}
| FLOAT {
    $$ = create_node(TYPE, "float", NULL, NULL);
}
| CHAR {
    $$ = create_node(TYPE, "char", NULL, NULL);
}
| DOUBLE {
    $$ = create_node(TYPE, "double", NULL, NULL);
}

var_list: var {
    $$ = create_node(VAR_LIST, $1, NULL, NULL);
}
| var_list COMMA var {
    $$ = create_node(VAR_LIST, $1, $3, NULL);
}

var: ID {
    $$ = create_node(VAR, $1, NULL, NULL);
}
| ID LBRACKET NUM RBRACKET {
    $$ = create_node(VAR, $1, create_node(NUMBER, $3, NULL, NULL), NULL);
}

stmt_list: /* empty */ {
    $$ = NULL;
}
| stmt_list stmt {
    $$ = create_node(STMT_LIST, $1, $2, NULL);
}

stmt: expr SEMICOLON {
    $$ = create_node(EXPR_STMT, $1, NULL, NULL);
}
| LBRACE stmt_list RBRACE {
    $$ = create_node(BLOCK, $2, NULL, NULL);
}
| IF LPAREN expr RPAREN stmt {
    $$ = create_node(IF_STMT, $3, $5, NULL);
}
| IF LPAREN expr RPAREN stmt ELSE stmt {
    $$ = create_node(IF_ELSE_STMT, $3, $5, $7);
}
| WHILE LPAREN expr RPAREN stmt {
    $$ = create_node(WHILE_STMT, $3, $5, NULL);
}
| FOR LPAREN expr SEMICOLON expr SEMICOLON expr RPAREN stmt {
    $$ = create_node(FOR_STMT, create_node(EXPR_STMT, $3, NULL, NULL), create_node(EXPR_STMT, $5, NULL, NULL), create_node(EXPR_STMT, $7, NULL, NULL), $9);
}
| DO stmt WHILE LPAREN expr RPAREN SEMICOLON {
    $$ = create_node(DO_WHILE_STMT, $4, $2, NULL);
}
| RETURN expr SEMICOLON {
    $$ = create_node(RETURN_STMT, $2, NULL, NULL);
}

expr: term {
    $$ = create_node(EXPR, $1, NULL, NULL);
}
| expr PLUS term {
    $$ = create_node(PLUS_EXPR, $1, $3, NULL);
}
| expr MINUS term {
    $$ = create_node(MINUS_EXPR, $1, $3, NULL);
}

term: factor {
    $$ = create_node(TERM, $1, NULL, NULL);
}
| term MULT factor {
    $$ = create_node(MULT_TERM, $1, $3, NULL);
}
| term DIV factor {
    $$ = create_node(DIV_TERM, $1, $3, NULL);
}
| term MOD factor {
    $$ = create_node(MOD_TERM, $1, $3, NULL);
}

factor: NUM {
    $$ = create_node(NUMBER, $1, NULL, NULL);
}
| ID {
    $$ = create_node(IDENTIFIER, $1, NULL, NULL);
}
| ID LBRACKET expr RBRACKET {
    $$ = create_node(ARRAY_ACCESS, $1, $3, NULL);
}
| LPAREN expr RPAREN {
    $$ = create_node(EXPR, $2, NULL, NULL);
}
| MINUS factor {
    $$ = create_node(NEG_FACTOR, $2, NULL, NULL);
}
| factor PLUS PLUS {
    $$ = create_node(POST_INC_FACTOR, $1, NULL, NULL);
}
| factor MINUS MINUS {
    $$ = create_node(POST_DEC_FACTOR, $1, NULL, NULL);
}
| SQUOTE ID SQUOTE {
    $$ = create_node(CHARACTER, $2, NULL, NULL);
}
| DQUOTE ID DQUOTE {
    $$ = create_node(STRING, $2, NULL, NULL);
}
| func_call {
    $$ = create_node(EXPR_STMT, $1, NULL, NULL);
}

func_call: ID LPAREN arg_list RPAREN {
    $$ = create_node(FUNC_CALL, $1, $3, NULL);
}

arg_list: /* empty */ {
    $$ = NULL;
}
| expr {
    $$ = create_node(ARG_LIST, $1, NULL, NULL);
}
| arg_list COMMA expr {
    $$ = create_node(ARG_LIST, $1, $3, NULL);
}

%%

int yylex();
void yyerror(char *);

int main() {
    yyparse();
    return 0;
}

void yyerror(char *s) {
    printf("%s\n", s);
}

以上代码演示了如何使用lex和yacc实现C语言的词法分析、语法分析，并输出抽象语法树。具体实现中还需要定义Node结构体和相关的操作函数，以及将yacc生成的AST传递到下一步的代码生成中。

使用lex和yacc编写一个C语言的语法分析器

1. 创建lex文件，命名为c_lex.l，输入以下内容：

%{
#include "c_yacc.tab.h"
%}

%%
"int" { return INT; }
"float" { return FLOAT; }
"char" { return CHAR; }
"if" { return IF; }
"else" { return ELSE; }
"while" { return WHILE; }
"for" { return FOR; }
"return" { return RETURN; }

[0-9]+ { yylval.num = atoi(yytext); return NUM; }

[a-zA-Z_][a-zA-Z0-9_]* { yylval.id = strdup(yytext); return ID; }

";" { return SEMICOLON; }
"," { return COMMA; }
"(" { return LEFTPAREN; }
")" { return RIGHTPAREN; }
"{" { return LEFTBRACE; }
"}" { return RIGHTBRACE; }

"==" { return EQ; }
">" { return GT; }
">=" { return GE; }
"<" { return LT; }
"<=" { return LE; }
"!=" { return NE; }
"=" { return ASSIGN; }

"//" { while(yyinput() != '\n'); }
"/*" { while(yyinput() != '*' || yyinput() != '/') yyinput(); }

[ \t\n] { }

. { printf("Error: unknown character %c\n", *yytext); }

%%

int yyinput(void)
{
return fgetc(yyin);
}

2. 创建yacc文件，命名为c_yacc.y，输入以下内容：

%{
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int yylex();
void yyerror(char *error);

int yyparse();

extern FILE *yyin;
extern int yylineno;
extern char *yytext;

%}

%token INT FLOAT CHAR IF ELSE WHILE FOR RETURN
%token NUM ID
%token SEMICOLON COMMA LEFTPAREN RIGHTPAREN LEFTBRACE RIGHTBRACE
%token EQ GT GE LT LE NE ASSIGN

%start program

%%

program: statement
;

statement: declaration
| assignment
| if_statement
| while_statement
| for_statement
| return_statement
| SEMICOLON
;

declaration: type ID SEMICOLON
;

assignment: ID ASSIGN expression SEMICOLON
;

if_statement: IF LEFTPAREN expression RIGHTPAREN LEFTBRACE statement RIGHTBRACE
| IF LEFTPAREN expression RIGHTPAREN LEFTBRACE statement RIGHTBRACE ELSE LEFTBRACE statement RIGHTBRACE
;

while_statement: WHILE LEFTPAREN expression RIGHTPAREN LEFTBRACE statement RIGHTBRACE
;

for_statement: FOR LEFTPAREN expression SEMICOLON expression SEMICOLON expression RIGHTPAREN LEFTBRACE statement RIGHTBRACE
;

return_statement: RETURN expression SEMICOLON
;

type: INT
| FLOAT
| CHAR
;

expression: expression EQ expression
| expression GT expression
| expression GE expression
| expression LT expression
| expression LE expression
| expression NE expression
| expression '+' expression
| expression '-' expression
| expression '*' expression
| expression '/' expression
| LEFTPAREN expression RIGHTPAREN
| ID
| NUM
;

%%
void yyerror(char *error)
{
printf("Error: %s at line %d\n", error, yylineno);
}

int main(int argc, char *argv[])
{
if(argc < 2)
{
printf("Usage: %s <filename>\n", argv[0]);
return 1;
}

FILE *fp = fopen(argv[1], "r");
if(!fp)
{
printf("Error: cannot open file %s\n", argv[1]);
return 1;
}

yyin = fp;
yyparse();

fclose(fp);

return 0;
}

3. 编译生成可执行文件，输入以下命令：

lex c_lex.l
yacc -d c_yacc.y
gcc lex.yy.c y.tab.c -o c_parser

4. 执行可执行文件，并输入要分析的C语言代码文件名，例如：

./c_parser test.c

其中test.c为要分析的C语言代码文件。