(完整版)《编译原理》词法分析程序设计方案

实验1-4 《编译原理》S语言词法分析程序设计方案

一、实验目的

了解词法分析程序的两种设计方法：1.根据状态转换图直接编程的方式；2.利用DFA 编写通用的词法分析程序。

二、实验内容

1．根据状态转换图直接编程

编写一个词法分析程序，它从左到右逐个字符的对源程序进行扫描，产生一个个的单词的二元式，形成二元式（记号）流文件输出。在此，词法分析程序作为单独的一遍，如下图所示。

具体任务有：

（1）组织源程序的输入

（2）拼出单词并查找其类别编号，形成二元式输出，得到单词流文件

（3）删除注释、空格和无用符号

（4）发现并定位词法错误，需要输出错误的位置在源程序中的第几行。将错误信息输出到屏幕上。

（5）对于普通标识符和常量，分别建立标识符表和常量表（使用线性表存储），当遇到一个标识符或常量时，查找标识符表或常量表，若存在，则返回位置，否则返回0并且填写符号表或常量表。

标识符表结构：变量名，类型（整型、实型、字符型），分配的数据区地址

注：词法分析阶段只填写变量名，其它部分在语法分析、语义分析、代码生成等阶段逐步填入。

常量表结构：常量名，常量值

2．编写DFA模拟程序

算法如下：

DFA（S=S0,MOVE[][],F[],ALPHABET[]）

/*S为状态，初值为DFA的初态，MOVE[][]为状态转换矩阵，F[] 为终态集，ALPHABET[] 为字母表，其中的字母顺序与MOVE[][] 中列标题的字母顺序一致。*/

{

Char Wordbuffer[10]=“”//单词缓冲区置空

Nextchar=getchar（）；//读

i=0；

while（nextchar！=NULL）//NULL代表此类单词

{ if （nextcha r！∈ALPHABET[]）{ERROR（“非法字符”），return（“非法字符”）；}

S=MOVE[S][nextchar] //下一状态

if（S=NULL）return（“不接受”）；//下一状态为空，不能识别，单词错误

wordbuffer[i]=nextchar ；//保存单词符号

i++；

nextchar=getchar（）；

}

Wordbuffer[i]=‘\0’;

If（S∈F）return（wordbuffer）；//接受

Else return（“不接受”）；

}

该算法要求：实现DFA算法，给定一个DFA（初态、状态转换矩阵、终态集、字母表），调用DFA（），识别给定源程序中的单词，查看结果是否正确。

三、实验要求

1．能对任何S语言源程序进行分析

在运行词法分析程序时，应该用问答形式输入要被分析的S源语言程序的文件名，然后对该程序完成词法分析任务。

2．能检查并处理某些词法分析错误

词法分析程序能给出的错误信息包括：总的出错个数，每个错误所在的行号，错误的编号及错误信息。

本实验要求处理以下两种错误（编号分别为1，2）：

1：非法字符：单词表中不存在的字符处理为非法字符，处理方式是删除该字符，给出错误信息，“某某字符非法”。

2：源程序文件结束而注释未结束。注释格式为：/* …… */

四、保留字和特殊符号表

单词的构词规则：

字母=[A-Za-z]

数字=[0-9]

标识符=字母（字母|数字）*

数字=数字(数字)*

四、S语言表达式和语句说明

1．算术表达式:+、-、*、/、%

2．关系运算符：>、>=、<、<=、==、！=

3．赋值运算符：=，+=、-=、*=、/=、%=

4．变量说明：类型标识符变量名表；

5．类型标识符：int char float

6．If语句：if 表达式then 语句[else 语句]

7．For语句：for（表达式1；表达式2；表达式3）语句8．While语句：while 表达式do 语句

9．S语言程序：由函数构成，函数不能嵌套定义。

函数格式为：

返回值函数名（参数）

begin

数据说明

语句

end

10．复合语句构成

begin

语句序列

end

五、程序参考结构说明

#include

#include

#include

#include

#define LIST_INIT_SIZE 100

#define LISTINCREMENT 10

#define OK 1

#define ERROR 0

#define Status int

typedef struct{

char key[20];

char num[10];

}ElemType;

typedef struct{

char num[10];

char sign[10];

char mnemonics[10];

char isn[10];

}ElemType2;

typedef struct{

ElemType *elem;

int length;

int listsize;

}SqList;

SqList L;

SqList L2;

int n=1;//行数

FILE *in,*out;// 指向文件的指针

char token[LISTINCREMENT];

char order_number[LIST_INIT_SIZE][LISTINCREMENT]=

{

"0","1","2","3","4","5","6","7","8","9","10",

"11","12","13","14","15","16","17","18","19","20",

"21","22","23","24","25","26","27","28","29","30",

"31","32","33","34","35","36","37","38","39","40",

"41","42","43","44","45","46","47","48","49","50",

};

ElemType key_world[14]=

{

{"int","0"},{"char","1"},{"float","2"},

{"void","3"},{"const","4"},{"for","5"},

{"if","6"},{"else","7"},{"then","8"},

{"while","8"},{"switch","9"},{"break","10"},

{"begin","11"},{"end","12"}

};

ElemType2 symbol[25]=

{

{"0","+","+","_"},{"1","-","-","_"},{"2","*","*","_"},

{"3","/","/","_"},{"4","%","%","_"},{"5","(","(","_"},

{"6",")",")","_"},{"7","[","[","_"},{"8","]","]","_"},

{"9","<","rlop","<"},{"9",">","rlop",">"},{"9","<=","rlop","<="},

{"9",">=","rlop",">="},{"9","==","rlop","=="},{"9","!=","rlop","!="}, {"10",";",";","_"},{"11","/=","/=","_"},

{"12","+=","+=","_"},{"13","-=","-=","_"},{"14","*=","*=","_"},

{"15","%=","%=","_"},{"16","||","or","_"},{"17","&&","and","_"},

{"18","!","not","_"},{"19","=","=","_"}

};