從存儲在鏈接列表中的CFG中刪除空值生成

Question

我的任務是使用C中的程序刪除CFG中的空值生成。答我只能使用鏈接列表。請注意，鏈接列表值部分指向一個數組。我在代碼中給出了輸出。我的空刪除產品無法正常工作。請運行代碼並告訴我您的想法以及如何改進。

#include <stdio.h> 
#include <ctype.h> 
#include <stdlib.h> 
#include <stdbool.h> 
/*the CFG 
S>ABAC 
A>aA|$ 
B>bB|$ 
C>c 
*/ 
/*List produced 
    SABAC 
    AaA 
    A$ 
    BbB 
    B$ 
    Cc*/ 
/*Desired Result 
    SABAC 
    SABC 
    SBAC 
    SBC 
    AaA 
    BbB 
    Bb 
    Cc*/ 
typedef struct node { 
    struct node * next; 
    //struct node * prev; 
    char arr[7];//the array to save CFG per line 
    }node_t; 
char print_list(node_t * root); 
//char first_set(node_t * root,char c); 
char traversal(node_t * root);//To see which nodes have null productions 
char rightTraversal(node_t * root,char);//Passing the nodes which have null production then removing them from list. 
char c, temp, nonTerminal; int i=0; bool flag = true; 
char null_list[7]; 
int null_counter = 0; 


int main() { 
    node_t * head = malloc(sizeof(node_t)); 
    node_t * current = malloc(sizeof(node_t)); 
    node_t * root = malloc(sizeof(node_t)); 
    head = current; 
    for(int j=0; j<7; j++){ 
     null_list[j] = '#'; 

    } 

    FILE *fp; 
    //char c, temp; int i=0; bool flag = true; 
    fp = fopen("cfg.txt", "r"); 
    while((c = fgetc(fp)) != EOF) { 
     if(c == '\n') { 
      current->next = malloc(sizeof(node_t)); 
      //current->next->next = NULL; 
      current = current->next; 
      current->next = NULL; 

      flag = true; i=0; 
     }else if(c == '>' || c == ' '){continue;} 
     else if(c == '|'){ 
      current->next = malloc(sizeof(node_t)); 
      current = current->next; 
      i = 0; 
      current->arr[i] = temp; 
      i++; 
      continue; 
     } 
     else { 
      current->arr[i] = c; 
      i++; 
      current->next = NULL; 
      //current->prev = NULL; 
      if(flag){ 
       temp = c; 
       flag = false; 
      } 
      // continue; 
     } 
    } 
    fclose(fp); 
    root = head; 

    traversal(root); 
    /*for(int j=0; j<7; j++){ 
     if(null_list[j] != '#'){ 
     printf("%c\n",null_list[j]); 
     } 
    }*/ 
    rightTraversal(root, null_list[0]); 
    rightTraversal(root, null_list[1]); 
} 
char print_list(node_t * root) { 
    while(root->next != NULL){ 
     for(i=0; i<7; i++) { 
      printf("%c", root->arr[i]); 
     } 
     printf("\n"); 
     root = root->next; 
    } 
    return 0; 
} 
char traversal(node_t * root) { 
    while(root->next != NULL){ 
     for(i=0; i<7; i++) { 
      if(root->arr[i] == '$'){ 
       null_list[null_counter] = root->arr[0]; 
       null_counter++; 

      } 
     } 
     root = root->next; 
    } 
    return 0; 
} 
char rightTraversal(node_t * root, char c){ 
    node_t * shoot = root; 
    while(shoot->next != NULL){ 
     for(int i=1; i<7; i++){ 
      if(shoot->arr[i] == c){ 
       node_t * temp_node = malloc(sizeof(node_t)); 
       /*printf("%c\n", shoot->arr[0]);*/ 

       for(int i=0; i<7; i++){ 
        temp_node->arr[i] = shoot->arr[i]; 
       } 
       for(int k=1; k<7; k++){ 
        if(temp_node->arr[k]==c){ 
         temp_node->arr[k] = ' '; 
         break; 
        } 
       } 
       temp_node->next = shoot->next; 
       shoot->next = temp_node; 
       break; 
       //shoot->next = malloc(sizeof(node_t)); 
       //shoot = shoot->next; 
      } 
     } 
     shoot = shoot->next; 
    } 
     print_list(root); 
} 

Answer 1

fgetc()返回int。您將結果分配給char。

所以這個條件

(c = fgetc(fp)) != EOF) 

永遠不會檢測EOF。

爲了解決這個問題定義c是一個int或引入一箇中間int這樣的：

int ci; 
while (ci = fgetc(fp)) != EOF) 
{ 
    c = ci; 

如果你想推高了編譯器的警告級別設置爲最大值（-Wall -Wextra -Wconversion -pedantic爲GCC）它大多喜歡有在此警告你！