词法分析器制作与应用
设计思想
(1)程序主体结构部分：
说明部分
%%
规则部分
%%
辅助程序部分
（2）主体结构的说明
在这里说明部分告诉我们使用的LETTER,DIGIT, IDENT(标识符,通常定义为字母开头的字母数字串)和STR(字符串常量,通常定义为双引号括起来的一串字符)是什么意思.这部分也可以包含一些初始化代码.例如用#include来使用标准的头文件和前向说明(forward ，references).这些代码应该再标记"%{"和"%}"之间;规则部分>可以包括任何你想用来分析的代码;我们这里包括了忽略所有注释中字符的功能,传送ID名称和字符串常量内容到主调函数和main函数的功能.
（3）实现原理
程序中先判断这个句语句中每个单元为关键字、常数、运算符、界符，对与不同的单词符号给出不同编码形式的编码，用以区分之。
PL/0语言的EBNF表示
<常量定义>：：=<标识符>=<无符号整数>;
<标识符>：：=<字母>={<字母>|<数字>};
<加法运算符>::=+|-
<乘法运算符>::=*|/
<关系运算符>::==|#|<|<=|>|>=
<字母>::=a|b|…|X|Y|Z
<数字>::=0|1|2|…|8|9
三：设计过程
1． 关键字：void，main，if，then，break，int，Char，float，include，for，while，printfscanf 并为小写。
2．"+”;”-”;”*”;”/”;”:=“;”:”;”<“;”<=“;”>“;”>=“;”<>“;”=“;”(“;”)”;”;”;”#”为运算符。
3． 其他标记 如字符串，表示以字母开头的标识符。
4． 空格符跳过。
5． 各符号对应种别码
关键字分别对应1-13
运算符分别对应401-418，501-513。
字符串对应100
常量对应200
结束符#
四：举例说明
目标：实现对常量的判别
代码：
digit [0-9]
letter [A-Za-z]
other_char [!-@\[-~]
id ({letter}|[_])({letter}|{digit}|[_])*
string {({letter}|{digit}|{other_char})+}
int_num {digit}+
%%
[ |\t|\n]+
"auto"|"double"|"int"|"struct"|"break"|"else"|"long"|"switch"|"case"|"enum"|"register"|"typedef"|"char"|"extern"|"return"|"union"|"const"|"float"|"short"|"unsigned"|"continue"|"for"|"signed"|"void"|"default"|"goto"|"sizeof"|"do"|"if"|"static"|"while"|"main" {Upper(yytext,yyleng);printf("%s,NULL\n",yytext);}
\"([!-~])*\" {printf("CONST_string,%s\n",yytext);}
-?{int_num}[.]{int_num}?([E][+|-]?{int_num})? {printf("CONST_real,%s\n",yytext);}
"0x"?{int_num} {printf("CONST_int,%s\n",yytext);}
","|";"|"("|")"|"{"|"}"|"["|"]"|"->"|"."|"!"|"~"|"++"|"--"|"*"|"&"|"sizeof"|"/"|"%"|"+"|"-"|">"|"<"|">="|"<="|"=="|"!="|"&"|"^"|"|"|"&"|"||"|"+="|"-="|"*="|"/="|"%="|">>="|"<<="|"&="|"^="|"|="|"=" {printf("%s,NULL\n",yytext);}
{id} {printf("ID,%s\n",yytext);}
{digit}({letter})+ {printf("error1:%s\n",yytext);}
%%
#include <ctype.h>
Upper(char *s,int l)
{
int i;
for(i=0;i<l;i++)
{
s[i]=toupper(s[i]);
}
}
yywrap()
{
return 1;
}
五：DFA
六:数据测试
七：心得体会
其实匹配并不困难，主要是C++知识要求相对较高，只要把握住指针就好了。
附源程序：
#include<iostream.h>
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
int i,j,k,flag,number,status;
/*status which is use to judge the string is keywords or not!*/
char ch;
char words[10] = {" "};
char program[500];
int Scan(char program[])
{
char *keywords[13] = {"void","main","if","then","break","int",
"char","float","include","for","while","printf",
"scanf"};
number = 0;
status = 0;
j = 0;
ch = program[i++];
/* To handle the lettle space ands tab*/
/*handle letters*/
if ((ch >= 'a') && (ch <= 'z' ))
{
while ((ch >= 'a') && (ch <= 'z' ))
{
words[j++]=ch;
ch=program[i++];
}
i--;
words[j++] = '\0';
for (k = 0; k < 13; k++)
if (strcmp (words,keywords[k]) == 0)
switch(k)
{
case 0:{
flag = 1;
status = 1;
break;
}
case 1:{
flag = 2;
status = 1;
break;
}
case 2:{
flag = 3;
status = 1;
break;
}
case 3:{
flag = 4;
status = 1;
break;
}
case 4:{
flag = 5;
status = 1;
break;
}
case 5:{
flag = 6;
status = 1;
break;
}
case 6:{
flag = 7;
status = 1;
break;
}
case 7:{
flag = 8;
status = 1;
break;
}
case 8:{
flag = 9;
status = 1;
break;
}
case 9:{
flag = 10;
status = 1;
break;
}
case 10:{
flag = 11;
status = 1;
break;
}
case 11:{
flag = 12;
status = 1;
break;
}
case 12:{
flag = 13;
status = 1;
break;
}
}
if (status == 0)
{
flag = 100;
}
}
/*handle digits*/
else if ((ch >= '0') && (ch <= '9'))
{
number = 0;
while ((ch >= '0' ) && (ch <= '9' ))
{
number = number*10+(ch-'0');
ch = program[i++];
}
flag = 200;
i--;
}
/*opereation and edge handle*/
else switch (ch)
{
case '=':{
if (ch == '=')
words[j++] = ch;
words[j] = '\0';
ch = program[i++];
if (ch == '=')
{
words[j++] = ch;
words[j] = '\0';
flag = 401;
}
else
{
i--;
flag = 402;
}
break;
}
case'>':{
if (ch == '>')
words[j++] = ch;
words[j] = '\0';
ch = program[i++];
if (ch == '=')
{
words[j++] = ch;
words[j] = '\0';
flag = 403;
}
else
{
i--;
flag = 404;
}
break;
}
case'<':{
if (ch == '<')
words[j++] = ch;
words[j] = '\0';
ch = program[i++];
if (ch == '=')
{
words[j++] = ch;
words[j] = '\0';
flag = 405;
}
else
{
i--;
flag = 406;
}
break;
}
case'!':{
if (ch == '!')
words[j++] = ch;
words[j] = '\0';
ch = program[i++];
if (ch == '=')
{
words[j++] = ch;
words[j] = '\0';
flag = 407;
}
else
{
i--;
flag = 408;
}
break;
}
case'+':{
if (ch == '+')
words[j++] = ch;
words[j] = '\0';
ch = program[i++];
if (ch == '=')
{
words[j++] = ch;
words[j] = '\0';
flag = 409;
}
else if (ch == '+')
{
words[j++] = ch;
words[j] = '\0';
flag = 410;
}
else
{
i--;
flag = 411;
}
break;
}
case'-':{
if (ch == '-')
words[j++] = ch;
words[j] = '\0';
ch = program[i++];
if (ch == '=')
{
words[j++] = ch;
words[j] = '\0';
flag = 412;
}
else if( ch == '-')
{
words[j++] = ch;
words[j] = '\0';
flag = 413;
}
else
{
i--;
flag = 414;
}
break;
}
case'*':{
if (ch == '*')
words[j++] = ch;
words[j] = '\0';
ch = program[i++];
if (ch == '=')
{
words[j++] = ch;
words[j] = '\0';
flag = 415;
}
else
{
i--;
flag = 416;
}
break;
}
case'/':{
if (ch == '/')
words[j++] = ch;
words[j] = '\0';
ch = program[i++];
if (ch == '=')
{
words[j++] = ch;
words[j] = '\0';
flag = 417;
}
else
{
i--;
flag = 418;
}
break;
}
case';':{
words[j] = ch;
words[j+1] = '\0';
flag = 501;
break;
}
case'(':{
words[j] = ch;
words[j+1] = '\0';
flag = 502;
break;
}
case')':{
words[j] = ch;
words[j+1] = '\0';
flag = 503;
break;
}
case'[':{
words[j] = ch;
words[j+1] = '\0';
flag = 504;
break;
}
case']':{
words[j] = ch;
words[j+1] = '\0';
flag = 505;
break;
}
case'{':{
words[j] = ch;
words[j+1] = '\0';
flag = 506;
break;
}
case'}':{
words[j] = ch;
words[j+1] = '\0';
flag = 507;
break;
}
case':':{
words[j] = ch;
words[j+1] = '\0';
flag = 508;
break;
}
case'"':{
words[j] = ch;
words[j+1] = '\0';
flag = 509;
break;
}
case'%':{
if (ch == '%')
words[j++] = ch;
words[j] = '\0';
ch = program[i++];
if (ch == '=')
{
words[j++] = ch;
words[j] = '\0';
flag = 510;
}
else
{
i--;
flag = 511;
}
break;
}
case',':{
words[j] = ch;
words[j+1] = '\0';
flag = 512;
break;
}
case'#':{
words[j] = ch;
words[j+1] = '\0';
flag = 513;
break;
}
case'@':{
words[j] = '#';
flag = 0;
break;
}
default:{
flag = -1;
break;
}
}
return flag;
}
main()
{
i=0;
printf("please input a program end with @");
do
{
ch = getchar();
program[i++] = ch;
}while(ch != '@');
i = 0;
do{
flag = Scan(program);
if (flag == 200)
{
printf("(%2d,%4d)",flag,number);
}
else if (flag == -1)
{
printf("(%d,error)",flag);
}
else
{
printf("(%2d,%4s)",flag,words);
}
}while (flag != 0);
system("pause");
}
基于Intel的可行性评估报告
http://blog.csdn.net/ctu_85/archive/2006/10/31/1357861.aspx
图象处理论文
http://blog.csdn.net/ctu_85/archive/2006/06/15/799857.aspx
linux论文
http://blog.csdn.net/ctu_85/archive/2006/06/12/791644.aspx
软件需求分析论文
http://blog.csdn.net/ctu_85/archive/2006/06/06/775892.aspx
英文翻译论文
http://blog.csdn.net/ctu_85/archive/2006/06/06/775165.aspx
图象分层论文
http://blog.csdn.net/ctu_85/archive/2006/06/07/777997.aspx
软件可行性分析论文
http://blog.csdn.net/ctu_85/archive/2006/06/06/775894.aspx
编译原理实验报告
http://blog.csdn.net/ctu_85/archive/2006/09/09/1198568.aspx
词法分析器制作与应用
