PL/0词法分析程序

　用C语言编写一个PL/0词法分析器，为语法语义分析提供单词，使之能把输入的字符串形式的源程序分割成一个个单词符号传递给语法语义分析，并把分析结果（基本字，运算符，标识符，常数以及界符）输出。

　　PL/0的词法分析程序GETSYM是一个独立的过程，其功能是为语法语义分析提供单词，把输入的字符串形式的源程序分割成一个个单词符号传递给语法语义分析。其主要任务为：1、滤空格；2、识别基本字；3、识别标识符；4、拼数；5、拼复合词；6、输出源程序。

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

using namespace std;
char stayWord[13][15] = {"const","var","procedure","begin","end","odd","if","then","call","while","do","read","write"};
char enumStayWord[13][15] = {"constsym","varsym","proceduresym","beginsym","endsym","oddsym","ifsym","thensym",
                            "callsym","whilesym","dosym","readsym","writesym"};
bool isNumber(char ch);
bool isCase(char ch);
bool isCaculationSymbol(char ch);
bool isBandSymbol(char ch);
int isStayWord(char *str);
void getInputStreamFromFile(char *fileName,char *str);
void calulationString(char *str);
void bandString(char *str);
void Analysis(char *InputFileName,char *str);

int main()
{
    char strr[100000],input[100]="E:\\编程验证\\input.txt";
    Analysis(input,strr);
    return 0;
}

bool isNumber(char ch){
    if(ch >='0' && ch <= '9') return true;
    return false;
}

bool isCase(char ch)
{
    if((ch >='a' && ch <='z') || (ch >= 'A'&& ch <='Z'))
        return true;
    return false;
}

bool isCaculationSymbol(char ch)
{
    if(ch == '+' || ch == '-' || ch == '/' || ch == '>' || ch == '<' || ch == '=' || ch == '#' || ch == ':')
        return true;
    return false;
}

bool isBandSymbol(char ch)
{
    if(ch == '(' || ch == ')'|| ch == ','|| ch ==';' || ch == '.')
        return true;
    return false;
}

int isStayWord(char *str)
{
     int i;
     for(i=0;i<13;++i){
            //printf("%s + !!\n",stayWord[i]);
        if(!strcmp(str,stayWord[i])) break;
     }
     return i;
}

void getInputStreamFromFile(char *fileName,char *str)
{
    char ch;
    int k=0;
    FILE *f;
    f = fopen(fileName,"r");
    while((ch=fgetc(f))!=EOF)
    {
        if(ch!='\n')
            str[k++] = ch;
        else
            str[k++]=' ';
    }
    str[k]='\0';
    fclose(f);
}

void calulationString(char *str)
{
    int len = strlen(str);
    int i;
    for(i=0;i<len;++i)
    {
        if(str[i] == '+') printf("  +  运算符/加号\n");
        else if(str[i] == '-') printf("  -  运算符/减号\n");
        else if(str[i] == '*') printf("  *  运算符/乘号\n");
        else if(str[i] == '/') printf("  /  运算符/除号\n");
        else if(str[i] == '=') printf("  =  运算符/等号\n");
        else if(str[i] == ':'){
            if(i+1<len && str[i+1] == '='){
                printf("  :=  运算符/赋值号\n");
                i++;
            }
            else
                printf("  %c  非法字符！\n",str[i]);
        }
        else if(str[i] == '#') printf("  #  运算符/不等于号\n");
        else if(str[i] == '>'){
            if(i+1<len && str[i+1] == '='){
                printf("  >=  逻辑运算符/大于等于号\n");
                i++;
            }
            else
                printf("  >  逻辑运算符/大于号\n");
        }
        else if(str[i] == '<'){
            if(i+1<len && str[i+1]=='='){
                printf("  <=  逻辑运算符/小于等于号\n");
                i++;
            }
            else
                printf("  <  逻辑运算符/小于号\n");;
        }
    }
}

void bandString(char *str)
{
    int len,i;
    len = strlen(str);
    for(i=0;i<len;++i)
    switch(str[i]){

       case '(': printf("  (  界符/左括号\n"); break;
       case ')': printf("  )  界符/右括号\n"); break;
       case ',': printf("  ,  界符/逗号\n"); break;
       case ';': printf("  ;  界符/分号\n"); break;
       case '.': printf("  .  界符/结束号\n"); break;
       default : break;
    }
}
void Analysis(char *InputFileName,char *str)
{
    getInputStreamFromFile(InputFileName,str);
    int len = strlen(str);
    int i,j,len1,len2,k,t,re;
    char str1[100],str2[100];
    i=0;
    while(i<len)
    {
        j=0;
        while(str[i] == ' '&& i<len) ++i;
        while(str[i] != ' '&& i<len) str1[j++] = str[i++];
        str1[j]='\0';
        len1 = strlen(str1);
        k=0;
        while(k<len1)
        {
            if(isCase(str1[k]))
            {
                t=0;
                while((!isCaculationSymbol(str1[k]))&&(!isBandSymbol(str1[k]))&&k<len1)
                    str2[t++] = str1[k++];
                str2[t]='\0';
                re = isStayWord(str2);
                if(re < 13)
                {
                    printf("  %s  基本字/%s\n",stayWord[re],enumStayWord[re]);
                    strcpy(str2,"");
                    t=0;
                }
                else
                {
                    printf("  %s  标识符\n",str2);
                    strcpy(str2,"");
                    t=0;
                }
            }
            else if(isNumber(str1[k]))
            {
                while(isNumber(str1[k])&&k<len1)
                    str2[t++] = str1[k++];
                str2[t]='\0';
                printf("  %s  常数\n",str2);
                strcpy(str2,"");
                t=0;
            }
            else if(isCaculationSymbol(str1[k])){
                while(isCaculationSymbol(str1[k])&&k<len1)
                    str2[t++] = str1[k++];
                str2[t] = '\0';
                calulationString(str2);
                strcpy(str2,"");
                t=0;
            }
            else if(isBandSymbol(str1[k]))
            {
                while(isBandSymbol(str1[k]) && k<len1)
                    str2[t++] = str1[k++];;
                str2[t] = '\0';
                bandString(str2);
                strcpy(str2,"");
                t=0;
            }
            else{
                printf("  字符串无法识别！\n"); k++;
            }
        }
        strcpy(str2,"");
    }
    fclose(stdout);
}

建立input.txt文件，修改文件路径即可使用。

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