词法分析施.cpp

简单的词法分析程序

#include<iostream.h>
#include<stdio.h>
#include<conio.h>
#include<string.h>
#define ID 6   //标识符
#define INT 7   //整数
#define LT 8  //小于
#define LE 9    //小于等于
#define EQ 10   //等于
#define NE 11     //不等于
#define GT 12    //大于
#define GE 13    //大于等于
#define ADD 14   //加"+"
#define SUB 15   //减"-"
#define MUL 16   //乘"*"
#define DIV 17   //除"/"
#define FH 18    //分号；
#define DH 19    //逗号，
#define ZHK 20   //左花括{
#define YHK 21   //右花括}
#define ZK 22    //左括（
#define YK 23    //右括）

char ch;
FILE *fp1,*fp2;

void get() //检查ch是否为空白符，是的话，继续取下一个字符，直到不为空
{
	while(ch==32||ch==10)	ch=fgetc(fp1);
}

int isalpha()  //判断ch是否为字母
{
	if((ch>='A')&&(ch<='Z')||(ch>='a')&&(ch<='z')) return 1;
	   else return 0;
}

int isalnum()  //判断ch是否为数字
{
	if(ch>='0'&&ch<='9')  return 1;
	   else return 0;
}

void report_error(char *ch)//报错
{
	fp2=fopen("out.txt","a");
	fseek(fp2,44L,0);
	fprintf(fp2,"<%s , error!>\n",ch);
	fclose(fp2); 
	cout<<ch<<"   error!"<<endl;
}


void out(int x,char *ch)  //输出函数，以二元组的形式从文件中输出
{
	cout<<x<<"   "<<ch<<endl;	
	fp2=fopen("out.txt","a");
	fseek(fp2,44L,0);
	fprintf(fp2,"<%d , %s>\n",x,ch);
	fclose(fp2); 
}

int lookup(char *TOKEN)   //判断TOKEN中的字符是否为关键字
{
	int key=0,i;
	char key_word[6][6]={"main","if","else","int","while","char"};
	for(i=0;i<6;i++)
		if(strcmp(TOKEN,key_word[i])==0) {key=i+1; break;}
	return key;
}


void scanner_example()  //扫描函数
{
	int i=0,c;
	char TOKEN[20];
	ch=fgetc(fp1);
	get();
	if(isalpha())//字母
	{
		TOKEN[0]=ch;
		ch=fgetc(fp1);
		i=1;
		while(isalpha())//指针右移查找下一个
		{
			TOKEN[i]=ch;
			ch=fgetc(fp1);
			i++;
		}
		TOKEN[i]='\0';
		fseek(fp1,-1L,1);//指针回返一个
		c=lookup(TOKEN);
		if(c==0) out (ID,TOKEN);//标识符
		else out(c,TOKEN);//单词
	}
	else 
		if(isalnum())//数字
		{
			TOKEN[0]=ch;
			ch=fgetc(fp1);
			i=1;
			while(isalnum())//指针右移查找下一个
			{
				TOKEN[i]=ch;
				ch=fgetc(fp1);
				i++;
			}
			fseek(fp1,-1L,1);
			TOKEN[i]='\0';
			out(INT,TOKEN);//整数
		}
		else
		switch(ch)//其他符号
		{
			case '<':ch=fgetc(fp1);
					 if(ch=='=') out(LE,"<=");//小于等于
						else if(ch=='>') out(NE,"<>");//不等于
							else
								{
									fseek(fp1,-1L,1);//指针回退一位
									out(LT,"<");//小于
								}
									break;
			case '=':out(EQ,"=");break;
			case '>':ch=fgetc(fp1);
					 if(ch=='=') out(GE,">=");//大于等于
						else
							{
								fseek(fp1,-1L,1);//指针回退一位
								out(GT,">");//大于
							}
								  break;
			case '+':out(ADD,"+");break;
			case '-':out(SUB,"-");break;
			case '*':out(MUL,"*");break;
			case '/':out(DIV,"/");break;
			case ';':out(FH,";"); break;
			case ',':out(DH,","); break;
			case '{':out(ZHK,"{");break;
			case '}':out(YHK,"}");break;
			case '(':out(ZK,"("); break;
			case ')':out(YK,")"); break;
	
		default:{TOKEN[0]=ch;TOKEN[1]='\0';report_error(TOKEN);break;}
	}
}

void main()
{
	char filename[20];
	printf("\n请输入文件(注意文件路径及类型<.cpp>哦) :");/*输入要编译文件的名字和路径*/ 
	scanf("%s",filename); 
	if((fp1=fopen(filename,"r"))==NULL) 	printf("您输入的文件名找不到!\n");
	fp2=fopen("out.txt","w");
    fclose(fp2);
   while(ch!=EOF)
   {
	   scanner_example(); 
   }
   fclose(fp1);
   getch();
}