c - 在c中编码词法分析器时出错

Question

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

/* this is a lexer which recognizes constants , variables ,symbols, identifiers , functions , comments and also header files . It stores the lexemes in 3 different files . One file contains all the headers and the comments . Another file will contain all the variables , another will contain all the symbols. */

int main()
{
    int i=0,j,k,count=0;
    char a,b[100],c[10000],d[100];
  memset ( d, 0, 100 );
    j=30;



    FILE *fp1,*fp2;


    fp1=fopen("source.txt","r"); //the source file is opened in read only mode which will passed through the lexer
    fp2=fopen("lext.txt","w");
    //now lets remove all the white spaces and store the rest of the words in a file


    if(fp1==NULL)
    {
        perror("failed to open source.txt");
        //return EXIT_FAILURE;
    }
    i=0;
    k=0;
    while(!feof(fp1))
    {


        a=fgetc(fp1);


        if(a!=' '&&a!='\n')
        {
                if (!isalpha(a))
                    {

                    switch(a)
                        {

                        case '+':{fprintf(fp2,"+ ---->  PLUS \n");
                                i=0;break;}
                        case '-':{fprintf(fp2,"- ---> MINUS \n");
                                i=0;break;}
                        case '*':{fprintf(fp2,  "* --->MULT \n");
                                i=0;break;}
                        case '/':{fprintf(fp2,  "/ --->DIV \n");
                                i=0;break;}
                        //case '+=':fprintf(fp2, "%.20s\n", "ADD_ASSIGN");
                        //case '-=':fprintf(fp2, "%.20s\n", "SUB_ASSIGN");
                        case '=':{fprintf(fp2,  "= ---> ASSIGN \n");
                                i=0;break;}
                        case '%':{fprintf(fp2,  "% ---> MOD \n");
                                i=0;break;}
                        case '<':{fprintf(fp2,  "< ---> LESSER_THAN \n");
                                i=0;break;}
                        case '>':{fprintf(fp2,  "> --> GREATER_THAN \n");
                                i=0;break;}
                        //case '++':fprintf(fp2, "%.20s\n", "INCREMENT");
                        //case '--':fprintf(fp2, "%.20s\n", "DECREMENT");
                        //case '==':fprintf(fp2, "%.20s\n", "ASSIGNMENT");
                        case ';':{fprintf(fp2,  "; --->SEMI_COLUMN \n");
                                i=0;break;}
                        case ':':{fprintf(fp2,  ": --->COLUMN \n");
                                i=0;break;}
                        case '(':{fprintf(fp2,  "( --->LPAR \n");
                                i=0;break;}
                        case ')':{fprintf(fp2,  ") --->RPAR \n");
                                i=0;break;}
                        case '{':{fprintf(fp2,  "{ --->LBRACE \n");
                                i=0;break;}
                        case '}':{fprintf(fp2,  "} ---> RBRACE \n");
                                i=0;break;}
                        }
                    }
            else
                {

                    d[i]=a;
                    //printf("%c\n",d[i]);
                    i=i+1;


                }
                        //}
                        /* we can make the lexer more complex by including even more depths of checks for the symbols*/









        }
        else
            {


            d[i+1]='\0';


        printf("\n");

            if((strcmp(d,"if ")==0)){fprintf(fp2,"if ---->  IDENTIFIER \n");
                        //printf("%s \n",d);
                         memset ( d, 0, 100 );
                        //printf("%s \n",d);
                        count=count+1;}

            else if(strcmp(d,"then")==0){fprintf(fp2,"then ---->  IDENTIFIER \n");
                        count=count+1;}

                else if(strcmp(d,"else")==0){fprintf(fp2,"else ----> IDENTIFIER  \n");
                            count=count+1;}

                else if(strcmp(d,"switch")==0){fprintf(fp2,"switch ----> IDENTIFIER  \n");
                            count=count+1;}
                else if(strcmp(d,"printf")==0){fprintf(fp2,"prtintf ----> IDENTIFIER  \n");
                            count=count+1;}
                else if(strcmp(d,"scanf")==0){fprintf(fp2,"scanf ----> IDENTIFIER  \n");
                            count=count+1;}
                else if(strcmp(d,"NULL")==0){fprintf(fp2,"NULL ----> IDENTIFIER  \n");
                            count=count+1;}
                else if(strcmp(d,"int")==0){fprintf(fp2,"INT ----> IDENTIFIER  \n");
                            count=count+1;}
                else if(strcmp(d,"char")==0){fprintf(fp2,"char ----> IDENTIFIER  \n");
                            count=count+1;}
                else if(strcmp(d,"float")==0){fprintf(fp2,"float ----> IDENTIFIER  \n");
                            count=count+1;}
                else if(strcmp(d,"long")==0){fprintf(fp2,"long ----> IDENTIFIER \n");
                            count=count+1;}
                else if(strcmp(d,"double")==0){fprintf(fp2,"double ----> IDENTIFIER \n");
                            count=count+1;}
                else if(strcmp(d,"const")==0){fprintf(fp2,"const ----> IDENTIFIER \n");
                            count=count+1;}
                else if(strcmp(d,"continue")==0)fprintf(fp2,"continue ----> IDENTIFIER \n");

                else if(strcmp(d,"size of")==0){fprintf(fp2,"size of ----> IDENTIFIER \n");
                            count=count+1;}
                else if(strcmp(d,"register")==0){fprintf(fp2,"register ----> IDENTIFIER \n");
                            count=count+1;}
                else if(strcmp(d,"short")==0){fprintf(fp2,"short ----> IDENTIFIER \n");
                            count=count+1;}
            else if(strcmp(d,"auto")==0){fprintf(fp2,"auto ----> IDENTIFIER \n");
                            count=count+1;}
                else if(strcmp(d,"while")==0){fprintf(fp2,"while ----> IDENTIFIER \n");
                            count=count+1;}
                else if(strcmp(d,"do")==0){fprintf(fp2,"do ----> IDENTIFIER \n");
                            count=count+1;}
                else if(strcmp(d,"case")==0){fprintf(fp2,"case ----> IDENTIFIER \n");
                            count=count+1;}
        else if (isdigit(d[i]))
            {
                fprintf(fp2,"%s ---->NUMBER",d);
            }
        else if (isalpha(a))
            {
                fprintf(fp2,"%s ----> Variable",d);
                //printf("%s",d);
                // memset ( d, 0, 100 );}
                //fprintf(fp2, "s\n", b);
                i=0;
        k=k+1;

                continue;
            }

        i=i+1;
    k=k+1;


    }
fclose(fp1);
fclose(fp2);
printf("%d",count);
return 0;
}

在此代码中，我的 source.txt 存储了 if (a+b) 。但只有 ( 、 + 和 ) 被写入 lext.txt，而不是标识符 if 或变量 a 和 b 。有什么具体原因吗？

Answer 1

存在不少问题:

一旦找到空格或换行符，您就尝试使用一系列 strcmp 来比较字符串 d 中的内容。但是您正在重置 else if (isalpha(a)) 主体中的 i 值，该值永远不会执行，因为 a 是空格或换行符。您应该立即无条件将i的值设置为0

d[i+1]='\0';

字符串中的空格很重要，因此

if((strcmp(d,"if ")==0)) // d will never have a space as you never stuff it with one.

应该是

if((strcmp(d,"if")==0))