[编译原理]一个词法分析器源码的剖析
一，词法分析器
作用：读取源程序的输入字符、将他们组成词素，生成并输出一个词法单元序列
二，设计原理
1）C程序语言的符号分类：关键字、标识符、常数、运算符、界符
2）词法分析器的二元输出：
3）正规式和状态转换图
4）程序说明：
1>main 中打开源码文件，从第一个字符流读取
2>如果第一个是字符，则交给letterprocess(str); 处理
3>如果第一个是数字，则交给numberprocess(str); 处理
4>如果第一个是数字，则交给otherprocess(str); 处理
5>注意上述过程中，File *fp每读取一个词素，fp都会移动到下一个词素。对于空格的处理：isspace（ch）检查参数c是否为空格字符，也就是判断是否为空格('')、定位字符
('\t')、CR('\r')、换行('\n')、垂直定位字符('\v')或翻页('\f')的情况
这个程序输出结果情况汇总：关键字、算术运算符、关系运算符、分割符号、特殊符号、注释符号、逻辑运算符、非法符号
三，程序源码
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#include
#include
#include
#include
#include
#include
#define NULL 0
FILE *fp;
char ch;
char *keyword[34]={"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", "printf",
"union","unsigned","void","volatile","while","main"};
char *operatornum[6]={"+","-","*","/","++","--"};
char *comparison[8]={"",">=","","==","!="};
char *interpunction[8]={",",";",":=",".","(",")","{","}"};
char *biaoshifu[6]={"%","$","^","&","_","#"};//特殊标识符
char *zhushifu[3]={"//","/*","*/"};//注释符
char *luoji[3]={"&&","||","!"};//逻辑运算符
bool search(char searchstr[],int wordtype)//符号匹配
{
int i;
switch (wordtype)
{
case 1:
for(i=0;i
{
if(strcmp(keyword[i],searchstr)==0)
return(true);
}
break;
case 2:
for(i=0;i
{
if(strcmp(operatornum[i],searchstr)==0)
return(true);
}
break;
case 3:
for(i=0;i
{
if(strcmp(comparison[i],searchstr)==0)
return(true);
}
break;
case 4:
for(i=0;i
{
if(strcmp(interpunction[i],searchstr)==0)
return(true);
}
break;
case 5:
for(i=0;i
{
if(strcmp(biaoshifu[i],searchstr)==0)
return(true);
}
break;
case 6:
for(i=0;i
{
if(strcmp(zhushifu[i],searchstr)==0)
return(true);
}
break;
case 7:
for(i=0;i
{
if(strcmp(luoji[i],searchstr)==0)
return(true);
}
break;
}
return false;
}
char letterprocess (char ch)//字母处理函数
{
int i=-1;
char letter[20];
while (isalnum(ch)!=0)
{
letter[++i]=ch;
ch=fgetc(fp);
}
letter[i+1]='\0';
if (search(letter,1))
{
printf("\n",letter);
//strcat(letter,"\n");
//fputs('\n',outp);
}
else
{
printf("\n",letter);
//strcat(letter,"\n");
//fputs(letter,outp);
}
return(ch);
}
char numberprocess(char ch)//数字处理程序
{
int i=-1;
char num[20];
while (isdigit(ch)!=0)
{
num[++i]=ch;
ch=fgetc(fp);
}
if(isalpha(ch)!=0)//数字后面是字符
{
while(isspace(ch)==0)
{
num[++i]=ch;
ch=fgetc(fp);
}
num[i+1]='\0';
printf("错误！非法标识符：%s\n",num);
goto u;
}
num[i+1]='\0';
printf("\n",num);
u: return(ch);
}
char otherprocess(char ch)//其他处理程序
{
int i=-1;
char other[20];
if (isspace(ch)!=0)
{
ch=fgetc(fp);
goto u;
}
while ((isspace(ch)==0)&&(isalnum(ch)==0))
{
other[++i]=ch;
ch=fgetc(fp);
}
other[i+1]='\0';
if (search(other,2))
printf("\n",other);
else if (search(other,3))
printf("\n",other);
else if (search(other,4))
printf("\n",other);
else if (search(other,5))
printf("\n",other);
else if (search(other,6))
printf("\n",other);
else if (search(other,7))
printf("\n",other);
else
printf("错误！非法字符：%s\n",other);
u: return (ch);
}
int main ()
{
char str;
printf("**********************************词法分析器************************************\n");
if ((fp=fopen("源程序.txt","r"))==NULL)
printf("源程序无法打开！\n");
else
{
str =fgetc(fp);//从流中读取字符
while (str!=EOF)
{
if (isalpha(str)!=0)//如果是字符 isalpha包含在#include
str=letterprocess(str);
else
{
if (isdigit(str)!=0)
str=numberprocess(str);
else
str=otherprocess(str);
}
};
printf("词法分析结束，谢谢使用！\n");
//printf("点任意键退出!\n");
}
//c=getch();
return 0;
}