Question

我已经开始学习 YACC 了，我已经执行了一些简单玩具程序的例子。但我从未见过一个实际的例子，演示了如何构建一个识别和实现函数定义和函数调用，数组实现的编译器等等使用谷歌搜索找到一个例子并不容易。有人可以提供一个如何使用YACC生成树的示例吗？ C或C ++很好。

提前致谢！

Answer 1

让我们用yacc解析这段代码。

文件测试包含我们要解析的有效C代码。

int main (int c, int b) {
    int a;
    while ( 1 ) {

    int d;
}
}

lex文件 c.l

alpha [a-zA-Z]
digit [0-9]

%%
[ \t]       ;
[ \n]   { yylineno = yylineno + 1;}
int return INT;
float return FLOAT;
char return CHAR;
void return VOID;
double return DOUBLE;
for     return FOR;
while   return WHILE;
if  return IF;
else    return ELSE;
printf  return PRINTF;
struct  return STRUCT;
^"#include ".+ ;
{digit}+       return NUM;
{alpha}({alpha}|{digit})* return ID;
"<="    return LE;
">="    return GE;
"=="    return EQ;
"!="    return NE;
">" return GT;
"<" return LT;
"."     return DOT;
\/\/.* ;
\/\*(.*\n)*.*\*\/ ;
.       return yytext[0];
%%

文件 c.y 输入YACC：

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

extern FILE *fp;

%}

%token INT FLOAT CHAR DOUBLE VOID
%token FOR WHILE
%token IF ELSE PRINTF
%token STRUCT
%token NUM ID
%token INCLUDE
%token DOT

%right '='
%left AND OR
%left '<' '>' LE GE EQ NE LT GT
%%

start:  Function
    | Declaration
    ;

/* Declaration block */
Declaration: Type Assignment ';'
    | Assignment ';'
    | FunctionCall ';'
    | ArrayUsage ';'
    | Type ArrayUsage ';'
    | StructStmt ';'
    | error
    ;

/* Assignment block */
Assignment: ID '=' Assignment
    | ID '=' FunctionCall
    | ID '=' ArrayUsage
    | ArrayUsage '=' Assignment
    | ID ',' Assignment
    | NUM ',' Assignment
    | ID '+' Assignment
    | ID '-' Assignment
    | ID '*' Assignment
    | ID '/' Assignment
    | NUM '+' Assignment
    | NUM '-' Assignment
    | NUM '*' Assignment
    | NUM '/' Assignment
    | '\'' Assignment '\''
    | '(' Assignment ')'
    | '-' '(' Assignment ')'
    | '-' NUM
    | '-' ID
    |   NUM
    |   ID
    ;

/* Function Call Block */
FunctionCall : ID'('')'
    | ID'('Assignment')'
    ;

/* Array Usage */
ArrayUsage : ID'['Assignment']'
    ;

/* Function block */
Function: Type ID '(' ArgListOpt ')' CompoundStmt
    ;
ArgListOpt: ArgList
    |
    ;
ArgList:  ArgList ',' Arg
    | Arg
    ;
Arg:    Type ID
    ;
CompoundStmt:   '{' StmtList '}'
    ;
StmtList:   StmtList Stmt
    |
    ;
Stmt:   WhileStmt
    | Declaration
    | ForStmt
    | IfStmt
    | PrintFunc
    | ';'
    ;

/* Type Identifier block */
Type:   INT
    | FLOAT
    | CHAR
    | DOUBLE
    | VOID
    ;

/* Loop Blocks */
WhileStmt: WHILE '(' Expr ')' Stmt
    | WHILE '(' Expr ')' CompoundStmt
    ;

/* For Block */
ForStmt: FOR '(' Expr ';' Expr ';' Expr ')' Stmt
       | FOR '(' Expr ';' Expr ';' Expr ')' CompoundStmt
       | FOR '(' Expr ')' Stmt
       | FOR '(' Expr ')' CompoundStmt
    ;

/* IfStmt Block */
IfStmt : IF '(' Expr ')'
        Stmt
    ;

/* Struct Statement */
StructStmt : STRUCT ID '{' Type Assignment '}'
    ;

/* Print Function */
PrintFunc : PRINTF '(' Expr ')' ';'
    ;

/*Expression Block*/
Expr:
    | Expr LE Expr
    | Expr GE Expr
    | Expr NE Expr
    | Expr EQ Expr
    | Expr GT Expr
    | Expr LT Expr
    | Assignment
    | ArrayUsage
    ;
%%
#include"lex.yy.c"
#include<ctype.h>
int count=0;

int main(int argc, char *argv[])
{
    yyin = fopen(argv[1], "r");

   if(!yyparse())
        printf("\nParsing complete\n");
    else
        printf("\nParsing failed\n");

    fclose(yyin);
    return 0;
}

yyerror(char *s) {
    printf("%d : %s %s\n", yylineno, s, yytext );
}

将Makefile放在一起的Makefile。我使用flex-lexer和bison，但该示例也适用于lex和yacc。

miniC:  c.l c.y
    bison c.y
    flex c.l
    gcc c.tab.c -ll -ly

编译并解析测试代码：

$ make
bison c.y
flex c.l
gcc c.tab.c -ll -ly
c.tab.c: In function ‘yyparse’:
c.tab.c:1273:16: warning: implicit declaration of function ‘yylex’ [-Wimplicit-function-declaration]
       yychar = yylex ();
                ^
c.tab.c:1402:7: warning: implicit declaration of function ‘yyerror’ [-Wimplicit-function-declaration]
       yyerror (YY_("syntax error"));
       ^
c.y: At top level:
c.y:155:1: warning: return type defaults to ‘int’ [-Wimplicit-int]
 yyerror(char *s) {
 ^
$ ls
a.out  c.l  CMakeLists.txt  c.tab.c  c.y  lex.yy.c  Makefile  README.md  test
$ ./a.out test

Parsing complete

对于阅读资源，我可以推荐书籍Modern Compiler Implementation in C by by Andrew Appe l和John Levine的flex / bison书。

如何编写yacc语法规则来识别函数定义与函数调用？

1 个答案: