recursivedropanalysis.c

语法分析器 对输入文法进行语法分析 自上而下

/* 4.6 递归下降分析法 */
#include <stdio.h>
#include <conio.h>
#include <stdlib.h>
#define INPUT_AND_DISPLAY();     /* 读一个单词的二元式并输出单词种别 */ \
                                fscanf(fileInput,"%c ",&t.code);\
                                fscanf(fileInput,"%s ",t.val); \
                                fputc(t.code,fileOutput);
void E(void);
void E1(void);
void T(void);
void T1(void);
void F(void);/* 函数原型 */
struct code_val{char code;char val[20];} t; /* 定义临时结构变量，存放单词二元式。 */
FILE *fileInput,*fileOutput;
int main(int argc,char *argv[])
{
    if(argc==1) /*参数个数为1，即46.exe，没输入文件名，例如fin.txt*/
    {
     printf("Have not enter file name.Press any key to exit...");
     getch();
     exit(0);
    }
    if((fileInput=fopen(argv[1],"rt"))==NULL)
    {      /*"rt",只读打开一个文本文件，只允许读数据*/
     printf("Cannot open %s\n",argv[1]);
     getch();
     exit(1);
    }
    if((fileOutput=fopen("fout.txt","wt+"))==NULL)
    {      /*"wt+",读写打开或建立一个文本文件，允许读写*/
     printf("Cannot create fout.txt FILE.Press any key to exit...");
     getch();
     exit(1);
    }
    INPUT_AND_DISPLAY();
    E( );
    if(t.code=='#')
        fprintf(fileOutput,"\nok\n");
    else
        fprintf(fileOutput,"\nerror in main()\n");
    fclose(fileInput);
    fclose(fileOutput);
    getch();
    return 0;
}
void E(void){/* E→T E' */
    if(t.code=='i'||t.code=='x'||t.code=='y'||t.code=='('){/* if (t.code∈first(T) */
        T( );E1( );
    }
    else{
    fprintf(fileOutput,"\nError in E()>%c\n",t.code);
        exit(0);
    }
}
void E1(void)/* E'→+TE'|ε,E'→-TE'|ε */
{
    if(t.code=='+'||t.code=='-'){
    INPUT_AND_DISPLAY();
        T( );E1( );
    }
    else if(!(t.code=='#'||t.code==')'))/* if(!t.code∈follow(E')) */
        fprintf(fileOutput,"\nError in E1()\n%c\n",t.code);
}
void T(void)/* T→FT' */
{
    if(t.code=='i'||t.code=='x'||t.code=='y'||t.code=='('){/* if(t.code∈first(F)) */
        F( );T1( );
    }
    else{
        fprintf(fileOutput,"\nError in T()>%c\n",t.code);exit(0);
    }
}
void T1(void)/* T'→*FT'|ε, T'→/FT'|ε*/
{
    if(t.code=='*'||t.code=='/'){
    INPUT_AND_DISPLAY();
        F( );T1( );
    }
    else if(!(t.code=='#'||t.code==')'||t.code=='+'||t.code=='-')){ /* if(!t.code∈follow(T')) */
        fprintf(fileOutput,"\nError in T1()>%c\n",t.code);exit(0);
    }
}
void F(void)/* F→(E)|i|x|y */
{
    if(t.code=='i'||t.code=='x'||t.code=='y'){ 
    INPUT_AND_DISPLAY();
    }
    else if(t.code=='('){
    INPUT_AND_DISPLAY();
        E( );
        if(t.code==')'){
     INPUT_AND_DISPLAY();
        }
        else{
            fprintf(fileOutput,"\nError in F1>%c\n",t.code);exit(0);
        }
    }
    else{
        fprintf(fileOutput,"\nError in F2>%c\n",t.code);exit(0);
    }
}