如何将文件中的信息存储到C中的内存中

Question

我需要逐行阅读文件并使用从每一行收集的信息进行一些操作。到目前为止，我的代码只能逐行读取文件并在控制台打印。

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

int main()
{
    printf("Hello world!\n");
    int x = 43; // number of lines in my text file
    FILE *fptr;
    struct values *valuesPtr = malloc(sizeof(struct values) * x);

    if (!valuesPtr)
        return -1;

    if((fptr = fopen("energy.txt", "r")) == NULL) {
        printf ("Error opening file ");
        return 0;
    }

    while (fptr != NULL) {
        for(int i = 0; i < x; i++ ) {
            fscanf(fptr, "%s %s %d", valuesPtr[i].start_vertex, valuesPtr[i].destination_vertex, &valuesPtr[i].num);
            printf("\nStart vertex: %s \nDestination vertex: %s \nWeight: %d\n\n", valuesPtr[i].start_vertex, valuesPtr[i].destination_vertex, valuesPtr[i].num);
        }
        free(valuesPtr);
    }
    fclose(fptr);

    return 0;
}

我的 structure.h 文件包含以下代码：

struct values{
    int num;
    char start_vertex[250];
    char destination_vertex[250];
} x;

energy.txt 文件具有以下内容：

York    Hull    60
Leeds   Doncaster   -47
Liverpool   Nottingham  161
Manchester  Sheffield   61
Reading Oxford  -43
Oxford  Birmingham  103
Birmingham  Leicester   63
Liverpool   Blackpool   79
Carlisle    Newcastle   92
Nottingham  Birmingham  77
Leeds   York    39
Glasgow Edinburgh   74
Moffat  Carlisle    65
Doncaster   Hull    76
Northampton Birmingham  90
Leicester   Lincoln 82
Sheffield   Birmingham  122
Lincoln Doncaster   63
Sheffield   Doncaster   29
Bristol Reading 130
Hull    Nottingham  145
Blackpool   Leeds   116
Birmingham  Bristol 139
Manchester  Leeds   64
Carlisle    Blackpool   140
Leicester   Northampton -61
Newcastle   York    135
Glasgow Moffat  -28
Leicester   Sheffield   100
Carlisle    Liverpool   -30
Birmingham  Manchester  129
Oxford  Bristol 116
Leeds   Hull    89
Edinburgh   Carlisle    154
Nottingham  Sheffield   61
Liverpool   Manchester  56
Carlisle    Glasgow 50
Sheffield   Lincoln 74
York    Doncaster   55
Newcastle   Edinburgh   177
Leeds   Sheffield   53
Northampton Oxford  68
Manchester  Carlisle    20

我被告知使用 getline() 函数和 sscanf() 来存储文件中的数据。但我不确定我应该怎么做。

Answer 1

你的代码有几个问题

有

    if((fptr = fopen("energy.txt", "r")) == NULL)
    {
        printf ("Error opening file ");
        return 0;
    }
    while (fptr != NULL)

如果 fptr 为 NULL，并且 fptr 的值，则无法到达 while永不改变while的正文，这样一个是无限循环

另一个问题是在 for 之后你释放了 valuesPtr 所以从第二个回合你将在释放的内存中写入，意外记忆。很可能 while 只是没用，可以删除（当然 for 不能）。

假设 while 完成你尝试释放 fptr，但这不是关闭描述的方式，你必须调用fclose(fptr) 而不是 free，你的 free 有一个未定义的行为

我鼓励您通过 fscanf 检查值 return，目前您无法知道它是否成功。请注意，fscanf 也可以写出包含字符串的字段，因为您不限制要读取的字符数。

当您无法打开文件时，您可以使用 perror:

给出原因

perror("Error opening file");

您修改后的提案：

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

typedef struct value {
  int num;
  char start_vertex[250];
  char destination_vertex[250];
} value;  

int main()
{
  const int nLines = 43; // number of lines in my text file
  FILE * fptr;
  value * valuesPtr = malloc(sizeof(value) * nLines);

  if (!valuesPtr) {
    puts("cannot allocate memory");
    return -1;
  }

  if((fptr = fopen("energy.txt", "r")) == NULL)
  {
    perror("Error opening file");
    return -1;
  }

  for(int i = 0; i < nLines; i++ )
  {
      if (fscanf(fptr, "%249s %249s %d",
                 valuesPtr[i].start_vertex, 
                 valuesPtr[i].destination_vertex, 
                 &valuesPtr[i].num) != 3) {
        printf("errored file line %d\n", i);
        break;
      }

      printf("\nStart vertex: %s \nDestination vertex: %s \nWeight: %d\n\n",
             valuesPtr[i].start_vertex, valuesPtr[i].destination_vertex, valuesPtr[i].num);
  }
  free(valuesPtr);
  fclose(fptr);

  return 0;
}

编译与执行：

pi@raspberrypi:/tmp $ gcc -Wall l.c
pi@raspberrypi:/tmp $ ./a.out

Start vertex: York 
Destination vertex: Hull 
Weight: 60


Start vertex: Leeds 
Destination vertex: Doncaster 
Weight: -47


Start vertex: Liverpool 
Destination vertex: Nottingham 
Weight: 161


Start vertex: Manchester 
Destination vertex: Sheffield 
Weight: 61


Start vertex: Reading 
Destination vertex: Oxford 
Weight: -43


Start vertex: Oxford 
Destination vertex: Birmingham 
Weight: 103


Start vertex: Birmingham 
Destination vertex: Leicester 
Weight: 63


Start vertex: Liverpool 
Destination vertex: Blackpool 
Weight: 79


Start vertex: Carlisle 
Destination vertex: Newcastle 
Weight: 92


Start vertex: Nottingham 
Destination vertex: Birmingham 
Weight: 77


Start vertex: Leeds 
Destination vertex: York 
Weight: 39


Start vertex: Glasgow 
Destination vertex: Edinburgh 
Weight: 74


Start vertex: Moffat 
Destination vertex: Carlisle 
Weight: 65


Start vertex: Doncaster 
Destination vertex: Hull 
Weight: 76


Start vertex: Northampton 
Destination vertex: Birmingham 
Weight: 90


Start vertex: Leicester 
Destination vertex: Lincoln 
Weight: 82


Start vertex: Sheffield 
Destination vertex: Birmingham 
Weight: 122


Start vertex: Lincoln 
Destination vertex: Doncaster 
Weight: 63


Start vertex: Sheffield 
Destination vertex: Doncaster 
Weight: 29


Start vertex: Bristol 
Destination vertex: Reading 
Weight: 130


Start vertex: Hull 
Destination vertex: Nottingham 
Weight: 145


Start vertex: Blackpool 
Destination vertex: Leeds 
Weight: 116


Start vertex: Birmingham 
Destination vertex: Bristol 
Weight: 139


Start vertex: Manchester 
Destination vertex: Leeds 
Weight: 64


Start vertex: Carlisle 
Destination vertex: Blackpool 
Weight: 140


Start vertex: Leicester 
Destination vertex: Northampton 
Weight: -61


Start vertex: Newcastle 
Destination vertex: York 
Weight: 135


Start vertex: Glasgow 
Destination vertex: Moffat 
Weight: -28


Start vertex: Leicester 
Destination vertex: Sheffield 
Weight: 100


Start vertex: Carlisle 
Destination vertex: Liverpool 
Weight: -30


Start vertex: Birmingham 
Destination vertex: Manchester 
Weight: 129


Start vertex: Oxford 
Destination vertex: Bristol 
Weight: 116


Start vertex: Leeds 
Destination vertex: Hull 
Weight: 89


Start vertex: Edinburgh 
Destination vertex: Carlisle 
Weight: 154


Start vertex: Nottingham 
Destination vertex: Sheffield 
Weight: 61


Start vertex: Liverpool 
Destination vertex: Manchester 
Weight: 56


Start vertex: Carlisle 
Destination vertex: Glasgow 
Weight: 50


Start vertex: Sheffield 
Destination vertex: Lincoln 
Weight: 74


Start vertex: York 
Destination vertex: Doncaster 
Weight: 55


Start vertex: Newcastle 
Destination vertex: Edinburgh 
Weight: 177


Start vertex: Leeds 
Destination vertex: Sheffield 
Weight: 53


Start vertex: Northampton 
Destination vertex: Oxford 
Weight: 68


Start vertex: Manchester 
Destination vertex: Carlisle 
Weight: 20

pi@raspberrypi:/tmp $

我冒昧地将values重命名为value因为struct保存了一个元素而不是几个，无论如何我鼓励您将其重命名为更精确的名称，value 非常笼统。我还使用了 typedef 来不必在每个使用它的地方都需要 struct。

查看详细信息，例如对于字符串，我使用格式 %249s 因为数组有 250 个字符（我为最后一个空字符删除了 1 个），并且当然我检查它读取 3 个元素。

如何将文件中的信息存储到C中的内存中

How do I store information from a file in to memory in C

c

linked-list

getline