使用lex和yacc编写一个C语言的语法分析器
时间: 2023-12-12 17:03:56 浏览: 37
以下是一个基本的C语言语法分析器示例,使用lex和yacc编写:
1. 首先,我们需要定义我们的C语言语法规则。下面是一个简单的示例:
```
program -> declaration_list
declaration_list -> declaration | declaration_list declaration
declaration -> var_declaration | func_declaration
var_declaration -> type_specifier ID ;
type_specifier -> int | float | double | char
func_declaration -> type_specifier ID ( params ) compound_stmt
params -> param_list | void
param_list -> param | param_list , param
param -> type_specifier ID
compound_stmt -> { local_declarations statement_list }
local_declarations -> local_declarations var_declaration | ε
statement_list -> statement | statement_list statement
statement -> expression_stmt | compound_stmt | selection_stmt | iteration_stmt | return_stmt
expression_stmt -> expression ;
selection_stmt -> if ( expression ) statement | if ( expression ) statement else statement
iteration_stmt -> while ( expression ) statement
return_stmt -> return ; | return expression ;
expression -> var = expression | simple_expression
var -> ID
simple_expression -> additive_expression relop additive_expression | additive_expression
additive_expression -> additive_expression addop term | term
term -> term mulop factor | factor
factor -> ( expression ) | var | call | NUM
call -> ID ( args )
args -> arg_list | ε
arg_list -> expression | arg_list , expression
```
2. 接下来,我们使用lex编写一个词法分析器,它将读取C代码并将其分解为标记流。以下是一个简单的示例:
```
%{
#include "y.tab.h"
%}
%%
"auto" return AUTO;
"break" return BREAK;
"case" return CASE;
"char" return CHAR;
"const" return CONST;
"continue" return CONTINUE;
"default" return DEFAULT;
"do" return DO;
"double" return DOUBLE;
"else" return ELSE;
"enum" return ENUM;
"extern" return EXTERN;
"float" return FLOAT;
"for" return FOR;
"goto" return GOTO;
"if" return IF;
"int" return INT;
"long" return LONG;
"register" return REGISTER;
"return" return RETURN;
"short" return SHORT;
"signed" return SIGNED;
"sizeof" return SIZEOF;
"static" return STATIC;
"struct" return STRUCT;
"switch" return SWITCH;
"typedef" return TYPEDEF;
"union" return UNION;
"unsigned" return UNSIGNED;
"void" return VOID;
"volatile" return VOLATILE;
"while" return WHILE;
[0-9]+ yylval.num = atoi(yytext); return NUM;
[a-zA-Z]+ yylval.name = strdup(yytext); return ID;
[ \t\n] /* ignore whitespace */
. return yytext[0];
%%
int yywrap() {
return 1;
}
```
3. 最后,我们使用yacc编写语法分析器,它将使用我们的语法规则和词法分析器生成的标记流来分析C代码。以下是一个简单的示例:
```
%{
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
%}
%token ID NUM AUTO BREAK CASE CHAR CONST CONTINUE DEFAULT DO DOUBLE ELSE ENUM EXTERN FLOAT FOR GOTO IF INT LONG REGISTER RETURN SHORT SIGNED SIZEOF STATIC STRUCT SWITCH TYPEDEF UNION UNSIGNED VOID VOLATILE WHILE
%%
program: declaration_list
;
declaration_list: declaration
| declaration_list declaration
;
declaration: var_declaration
| func_declaration
;
var_declaration: type_specifier ID ';'
;
type_specifier: INT
| FLOAT
| DOUBLE
| CHAR
;
func_declaration: type_specifier ID '(' params ')' compound_stmt
;
params: param_list
| VOID
;
param_list: param
| param_list ',' param
;
param: type_specifier ID
;
compound_stmt: '{' local_declarations statement_list '}'
;
local_declarations: local_declarations var_declaration
| /* empty */
;
statement_list: statement
| statement_list statement
;
statement: expression_stmt
| compound_stmt
| selection_stmt
| iteration_stmt
| return_stmt
;
expression_stmt: expression ';'
;
selection_stmt: IF '(' expression ')' statement
| IF '(' expression ')' statement ELSE statement
;
iteration_stmt: WHILE '(' expression ')' statement
;
return_stmt: RETURN ';'
| RETURN expression ';'
;
expression: var '=' expression
| simple_expression
;
var: ID
;
simple_expression: additive_expression relop additive_expression
| additive_expression
;
additive_expression: additive_expression addop term
| term
;
term: term mulop factor
| factor
;
factor: '(' expression ')'
| var
| call
| NUM
;
call: ID '(' args ')'
;
args: arg_list
| /* empty */
;
arg_list: expression
| arg_list ',' expression
;
relop: '<'
| LE
| '>'
| GE
| EQ
| NE
;
addop: '+'
| '-'
;
mulop: '*'
| '/'
;
%%
int main() {
yyparse();
return 0;
}
void yyerror(char *s) {
printf("Error: %s\n", s);
}
```
这是一个基本的C语言语法分析器示例,它将读取C代码并检查它是否符合我们的语法规则。需要注意的是,这只是一个简单的示例,实际的C语言语法规则远比这个复杂,因此需要更复杂的词法和语法规则来处理它。