PL/0 词法分析器

PL/0 词法分析器

 

#include<stdio.h>
#include <ctype.h>
#include <stdlib.h>
#include <string.h>

typedef enum SymEnum
{
    Identifier=0, //标识符
    Const=1,  //常数
    Key=2,    //关键字
    Operator=3,   //运算符
    Delimiter=4   //界符
} SymEnum;

char KeyWord[13][15];    //关键字

void Init()
{
    strcpy(&KeyWord[0][0],"begin");
    strcpy(&KeyWord[1][0],"call");
    strcpy(&KeyWord[2][0],"const");
    strcpy(&KeyWord[3][0],"do");
    strcpy(&KeyWord[4][0],"end");
    strcpy(&KeyWord[5][0],"if");
    strcpy(&KeyWord[6][0],"odd");
    strcpy(&KeyWord[7][0],"procedure");
    strcpy(&KeyWord[8][0],"read");
    strcpy(&KeyWord[9][0],"then");
    strcpy(&KeyWord[10][0],"var");
    strcpy(&KeyWord[11][0],"while");
    strcpy(&KeyWord[12][0],"write");
}

//判断一个单词是否为关键字
int IsKeyWord(char *word)
{
    int i=0,j=12;
    while(i<=j)
    {
        int k=(i+j)/2;
        if(strcmp(word,KeyWord[k])<=0)
            j=k-1;
        if(strcmp(word,KeyWord[k])>=0)
            i=k+1;
    }
    return i-1>j ? 1 : 0;
}

//判断一个单词是否为界符
int IsDelimiter(char word)
{
    if(word==','||word==';'||word=='.'||word=='('||word==')')
        return 1;
    return 0;
}

//判断一个单词是否为操作符
int IsOperator(char *word)
{
    if(word[0]=='+'||word[0]=='-'||word[0]=='*'||word[0]=='/'||word[0]=='<'||word[0]=='>'||strcmp(word,":=")==0||strcmp(word,">=")==0||strcmp(word,"<=")==0||word[0]=='#'||word[0]=='=')
        return 1;
    return 0;
}

//判断一个单词是否是常数
int IsConst(char *word)
{
    if(word[0]>='0'&&word[0]<='9')
        return 1;
    return 0;
}

//判断连个字符是否属于相同类型
int IsSame(char f,char s)
{
    int bf = (f>='0'&&f<='9'||f>='a'&&f<='z'||f>='A'&&f<='Z')?  1 : 0 ;
    int bs = (s>='0'&&s<='9'||s>='a'&&s<='z'||s>='A'&&s<='Z')?  1 : 0 ;
    return bf == bs;
}

//判断 word 的类型
SymEnum TypeOfWord(char *word)
{
    if(IsKeyWord(word))
        return Key;
    if(IsConst(word))
        return Const;
    if(IsOperator(word))
        return Operator;
    return Identifier;
}

int GetSym()
{
    FILE *fp,*fout;
    if((fp=fopen("PL0.txt","r"))==NULL || (fout=fopen("source.txt","w+"))==NULL)
    {
        printf("Open Error!\n");
        exit(0);
    }
    SymEnum SYM;    //存放每个单词的类别，用内部编码形式表示；
    char word[50];  //存储单词
    word[0]='\0';
    int len=0;      //单词长度
    char ch;
    while(fscanf(fp,"%c",&ch)!=EOF)
    {
        // ch 为空格，回车符，制表符
        if(ch==' '||ch=='\n'||ch=='\t')
        {
            // word 不为空
            if(len)
            {
                //判断单词类型
                SYM=TypeOfWord(word);
                fprintf(fout,"%d %s\n",SYM,word);
                //清空缓存区
                len=0;
                word[len]='\0';
            }
            // word 为空，忽略 ch
        }
        else if(IsDelimiter(ch))
        {
            //word 不为空
            if(len)
            {
                //判断单词的类型
                SYM=TypeOfWord(word);
                fprintf(fout,"%d %s\n",SYM,word);
                // ch == delimiter
                SYM=Delimiter;
                fprintf(fout,"%d %c\n",SYM,ch);
                //清空缓存区
                len=0;
                word[len]='\0';
            }
            else
            {
                //word 为空, ch 为界符
                SYM=Delimiter;
                fprintf(fout,"%d %c\n",SYM,ch);
                //清空缓存区
                len=0;
                word[len]='\0';
            }
        }
        else
        {
            if(len>0)
            {
                if(IsSame(word[len-1],ch))
                {
                    //判断 word 与 ch 是否同类型
                    word[len++]=ch;
                    word[len]='\0'; //字符串终结符
                }
                else
                {
                    //判断单词类型
                    SYM=TypeOfWord(word);
                    fprintf(fout,"%d %s\n",SYM,word);
                    //清空缓存区，并把 ch 放入缓存区
                    len=0;
                    word[len++]=ch;
                    word[len]='\0'; //字符串终结符
                }
            }
            else
            {
                word[len++]=ch;
                word[len]='\0';
            }
        }
    }
    fclose(fp);
    fclose(fout);
    return 0;
}

void PrintToScream()
{
    FILE *fp;
    if((fp=fopen("source.txt","r+"))==NULL)
    {
        printf("Open File Error!\n");
        exit(0);
    }
    int id;
    char word[50];
    printf("0-标识符 1-常数 2-关键字 3-操作符 4-界符\n");
    while(fscanf(fp,"%d %s",&id,word)!=EOF)
    {
        printf("(%d,%s)\n",id,word);
    }
    fclose(fp);
}

int main()
{
    Init();
    GetSym();
    PrintToScream();
    return 0;
}