Question

如何将文本文件中的数据直接转换为结构指针？我试着这个，但我不能让它工作，文本文件的例子可以是：

A 100

K 55

C 300等

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

struct myStruct
{
    char singleChar[10];
    int height;
};

int main (void) {

    FILE * fp;
    char buffer[50];
    int counter = 0;
    char a[10];
    int res;
    int b;
    struct myStruct **list;
    list = malloc(sizeof(struct myStruct));

    fp = fopen("test.txt","r");  
    while (fgets(buffer,50,fp)!= NULL)
    {
        res = sscanf(buffer, "%c%d",a,&b);
        if (res == 2) 
        {
            list[counter] = malloc(sizeof(struct myStruct));
            strcpy(list[counter]->singleChar,a);
            list[counter]->height = b;
            counter++;
        }
    }

    printf("%d",list[0]->height);

    return 0;    
}

Answer 1

如果您不知道文件的大小，则必须对其进行完整传递以确定其长度，然后再次扫描以将数据加载到结构中：

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

struct myStruct
{
    char singleChar[10];
    int height;
};

int main (void) {

    FILE * fp;
    int counter = 0;
    char a[10];
    int b, i;
    int file_length = 0;

    fp = fopen("test.txt","r");
    while (fscanf(fp, "%c%d\n",a,&b) > 0){
        printf("%c,%d\n",a[0],b);
        file_length += 1;
    }
    printf("There are %d entries\n",file_length);

    struct myStruct *list[file_length];

    fclose(fp);
    fp = fopen("test.txt","r");
    while ( fscanf(fp, "%c%d\n",a,&b) > 0 ){
        list[counter] = malloc(sizeof(struct myStruct));
        strcpy(list[counter]->singleChar,a);
        list[counter]->height = b;
        counter += 1;
    }

    for ( i = 0 ; i < file_length ; i++ ){
        printf("%c,%d\n",list[i]->singleChar[0],list[i]->height);
        free(list[i]);
    }

    return 0;
}

另一种方法是分配使用realloc。

为什么在struct中使用char数组而不是单个char？

Answer 2

您可能想要使用链接列表：

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

struct List
{
char c;
int i;
struct List* lp;
};

typedef struct List LinkedList;
_Bool first_time_here=1;

LinkedList *head,*tmp;

int main(void)
{

char tempc,nl;
int tempd;
LinkedList* ptr;
LinkedList* current=NULL;
FILE* fp; 

if((fp=fopen("36229327.txt","r"))!=NULL)
{
  printf("Contents from file\n");
  while(fscanf(fp,"%c%d%c",&tempc,&tempd,&nl)>0)
    {
          printf("%c %d\n",tempc,tempd);
      ptr=malloc(1*sizeof(LinkedList)); 
      if(ptr != NULL)
      {
      if(first_time_here)
      {
      head=ptr;
      first_time_here=0;
      }
      ptr->c=tempc;
      ptr->i=tempd;
      ptr->lp=NULL;
      if(current!=NULL)
       {
         current->lp=ptr; 
       }
      current=ptr;
      }
      else
      {
      printf("Can't allocate memory\n");
      printf("Aborting\n");
      }
    }

    fclose(fp);
    printf("\nFile Closed\n\n");
if(head!=NULL)
{
current=head;
printf("File contents retrieved from Linked List\n");
while(current!=NULL)
{
  printf("%c %d\n",current->c,current->i);
  tmp=current;
  current=current->lp;
  free(tmp); // clearing the allocated memory
}
}
}
else
{
printf("Can't open file\n");
exit(-1);
}

return 0;
}

从代码中可以看出，内存是按需创建的，并在使用后释放。

假设：文件内容的存储方式与问题中给出的完全相同在行尾没有多余的空格。

将数据读入struct

2 个答案: