无论是词法分析，还是语法分析，给我的第一感觉就是逻辑要严谨。由于项目有自己一套完整的语言和语法，设计好其对应的词法分析器和语法分析器显得尤为重要。

这里给您提供一个免费的java词法分析器下载

java词法分析器实现原理步骤

先写其正则式，然后NFA，然后DFA，然后对其进行优化，最后准备工作做好了，就可以开始写代码了。

下面对其里面的主要函数进行讲解：

enum Token_Type {

keyword =1,              //关键字

Identifier,            //标识符

operatorr,             //运算符

operatorrd,             //单运算符

constant,              //常量

escape,                //转义符

separator,              //界限符

notype,                  //没有类型

zhushi                   //注释类型

};

对其单词的类型定义成枚举。

typedef struct Token {

Token_Type type; //其类型

char *lexeme ;    //字符串

int  value;       //属性值

}Token;

//返回单词的结构。

void InitScanner(char *ch){

fp1 = fopen(ch,"r+");

LineNo = 1;

}//初始化分析器。

void CloseScanner(){

fclose(fp1);

}//关闭分析器

void EmptyTokenString(){

memset(TokenBuffer,0,100);

}//清空缓冲区

static void AddCharTokenString(char Char)

{

int TokenLenth=strlen(TokenBuffer);

if(TokenLenth+1==sizeof(TokenBuffer)) return;

TokenBuffer[TokenLenth]=Char;

TokenBuffer[TokenLenth+1]='\0';

} //将一个字符添加到缓冲区

static char GetChar(){

char Char;

Char = fgetc(fp1);

return Char;

}//从文件中读取一个字符

static void BackChar(char Char) {

if(Char!=EOF){

ungetc(Char,fp1);

}

}//将其字符后退一个。

static Token JudgeKeyToken(char *IDstring)；//这个函数实现对关键字进行判断

下面是源代码：

/************************************************************************

*                CopyRight@ice-snow studio                              *

*               email:bingxuefenggu@126.com                             *

*               qq: 405116890                                           *

************************************************************************/

//只考虑到整形常量

//实型没考虑到

//需要解决转义符如何描述的问题

#include

#include

#include

#include

#define TOKEN_LEN 100

enum Token_Type {

keyword =1,              //关键字

Identifier,            //标识符

operatorr,             //运算符

operatorrd,             //单运算符

constant,              //常量

escape,                //转义符

separator,              //界限符

notype,                  //没有类型

zhushi                   //注释类型

};

typedef struct Token {

Token_Type type; //其类型

char *lexeme ;    //字符串

int  value;       //属性值

}Token;

static Token Token_Tap[] = {

{keyword,"abstract",0x103},

{keyword,"boolean",0x103},

{keyword,"break", 0x103},

{keyword,"byte" ,0x103},

{keyword,"case",0x103},

{keyword,"catch",0x103},

{keyword,"char", 0x103},

{keyword, "class",0x103},

{keyword,"const" ,0x103},

{keyword,"continue" ,0x103},

{keyword,"default" , 0x103},

{keyword,"do",0x103},

{keyword,"double",0x103},

{keyword,"else",0x103},

{keyword,"extends",0x103},

{keyword,"false",0x103},

{keyword,"final",0x103},

{keyword,"finally",0x103},

{keyword,"float",0x103},

{keyword,"for",0x103},

{keyword,"goto",0x103},

{keyword,"if",0x103},

{keyword,"implements",0x103},

{keyword,"import",0x103},

{keyword,"instanceof",0x103},

{keyword,"int",0x103},

{keyword,"interface",0x103},

{keyword,"long",0x103},

{keyword,"native",0x103},

{keyword,"new",0x103},

{keyword,"null",0x103},

{keyword,"package",0x103},

{keyword,"private",0x103},

{keyword,"protected",0x103},

{keyword,"public",0x103},

{keyword,"return",0x103},

{keyword,"short",0x103},

{keyword,"static",0x103},

{keyword,"super",0x103},

{keyword,"switch",0x103},

{keyword,"synchronized",0x103},

{keyword,"this",0x103},

{keyword,"throw",0x103},

{keyword,"throws",0x103},

{keyword,"transient",0x103},

{keyword,"true",0x103},

{keyword,"try", 0x103},

{keyword,"void",0x103},

{keyword,"volatile",0x103},

{keyword,"while",0x103},

{constant,"true",0x105},

{constant,"false",0x105}

//以上是所有的关键字

};

FILE *fp1;// 要读文件的描述符

int LineNo;//单词所在的行数

static char TokenBuffer[TOKEN_LEN];//单词符号的缓存区

void InitScanner(char *ch){

fp1 = fopen(ch,"r+");

LineNo = 1;

}

void CloseScanner(){

fclose(fp1);

}

void EmptyTokenString(){

memset(TokenBuffer,0,100);

}

static void AddCharTokenString(char Char)

{

int TokenLenth=strlen(TokenBuffer);

if(TokenLenth+1==sizeof(TokenBuffer)) return;

TokenBuffer[TokenLenth]=Char;

TokenBuffer[TokenLenth+1]='\0';

}

static char GetChar(){

char Char;

Char = fgetc(fp1);

return Char;

}

static void BackChar(char Char) {

if(Char!=EOF){

ungetc(Char,fp1);

}

}

static Token JudgeKeyToken(char *IDstring){

int loop;

Token token;

for(loop=0;loop<51;loop++){

if(strcmp(Token_Tap[loop].lexeme,IDstring)==0)

return Token_Tap[loop];

}

token.type = Identifier;

//strcpy(token.lexeme,IDstring);//youwenti.

token.lexeme = IDstring;

token.value = 0x104;

return token;

}

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