Question

我目前正在尝试处理一个逐行读取文件并将内容放在数组中的程序。然后尝试将原始数组反转为第二个数组，以便稍后比较两个数组。我目前的代码是

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

     void reversing(char buffer[], char reverse[], int stringLength);

     int main(int argc, char const *argv[])
     {
        int stringLength = 0;
        FILE *fp;   //Declaring a FILE type pointer calling it fp
        char buffer[64]; //Declaring a char array the size of 64 named buffer

        fp = fopen("./test.txt", "r"); 
        if(fp == NULL)
        {
          printf("File did not open!\n");
        }
        else
        {
              while(fgets(buffer, 64, (FILE*)fp) != NULL)
              {
                 printf("\nNormal String: %s", buffer); //Print content in buffer(original array)
                 stringLength = strlen(buffer);        //Storing the length of the readed input

                 char reverse[stringLength];  //Creating array for reversed comparision(comparision not implemented yet)

                 printf("String length: %d\n", stringLength); //Print string length(for debugging)
                 reversing(buffer, reverse, stringLength);
                 printf("Reversed String: %s\n", reverse);//Print content in reverse(Reverse array)
             }

             printf("\n\nEND OF FILE Reached!\n");

             fclose(fp);
       }    
        return 0;
    }

    void reversing(char buffer[], char reverse[], int stringLength)
    {
       int i = 0;
       int j = stringLength - 1;

       while(i < j)
       {
       reverse[j] = buffer[i];
       i++;
       j--;
       }
    }

我的测试文件只是

    A
    AB
    ABC
    ABCD
    ABCDE

它应该打印到屏幕

   Normal String:   A
   Reversed String: A 
   Normal String:   AB 
   Reversed String: BA
   Normal String:   ABC 
   Reversed String: CBA
   Normal String:   ABCD 
   Reversed String: DCBA
   Normal String:   ABCDE 
   Reversed String: EDCBA

当我通过调试器运行程序时，它显示一旦在反转功能内部，字母正确交换;然而，一旦它退出该函数并且打印反向数组的调用是打印垃圾，但在垃圾内部是前两个元素正确交换。任何建议的帮助将不胜感激。

As a side note我试图让这个变得尽可能简单，因为真正的目标或者这个程序是在ci20机器上装配并实现它。

Answer 1

stringLength = strlen(buffer); //Storing the length of the readed input

char reverse[stringLength];   //Creating array for reversed comparision(comparision not implemented yet)

您没有足够的空间存储尾随\0

char reverse[stringLength];

应该是

char reverse[stringLength + 1];

并且不要忘记在反向函数的最后添加此traling \0：

reverse[stringLength] = '\0';

但是请注意（在这种情况下）你不需要临时来反转字符串，只需传递原始字符串并交换直到达到NUL字符，看看How do you reverse a string in place in C or C++?

Answer 2

如果您正在寻找一个非常简单的解决方案，可以使用string.h库中的strrev。它为你翻转字符串，这意味着你不必自己进行字符串反转功能。你可以改为调用它。

这样的事情：

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

#define BUFFSIZE 64

int
main(void) {
    FILE *filename;
    char buffer[BUFFSIZE];
    int length;

    filename = fopen("test.txt", "r");

    if (filename == NULL) {
        fprintf(stderr, "%s\n", "Error Reading File!");
        exit(EXIT_FAILURE);
    }

    while (fgets(buffer, BUFFSIZE, filename) != NULL) {
        length = strlen(buffer)-1;

        if (buffer[length] == '\n') {
            buffer[length] = '\0';
        }

        printf("Normal String: %s\n", buffer);
        printf("Reversed String: %s\n", strrev(buffer));
    }
    return 0;
}

Answer 3

你的问题在于你的逆转功能中的while (i < j)行。当只有一半的数组被反转时，i最终会小于j。相反，它应该是while (i < stringLength)

您还应该将字符数组char reverse[stringLength]更改为char reverse[stringLength + 1]，以便为'\0'终止字符留出空间，您应该在反转功能结束时添加到数组中。

它应该是这样的：

void reversing(char buffer[], char reverse[], int stringLength)
{
    int i = 0;
    int j = stringLength - 1;

    while(i < stringLength)
    {
        reverse[j] = buffer[i];
        i++;
        j--;
    }
    reverse[i] = '\0';
}

另请注意，文件的读取功能也在读取换行符，并且反转功能将其放在反向字符串的开头，因此输出如下所示：

Normal String: A
String length: 2
Reversed String: 
A

Normal String: AB
String length: 3
Reversed String: 
BA

Normal String: ABC
String length: 4
Reversed String: 
CBA

Normal String: ABCD
String length: 5
Reversed String: 
DCBA

Normal String: ABCDE
String length: 6
Reversed String: 
EDCBA


END OF FILE Reached!

在将换行符发送到反转功能之前，我会让你知道删除换行符。如果您无法弄清楚，只需在此答案下对其进行评论，我就会编辑答案。

Answer 4

为了解决我扭转数组并忘记'\0'的问题，没有为'\0'留出足够的空间，并处理fgets添加换行符。这是我当前正确运行的代码。

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

    void reversing(char buffer[], char reverse[], int stringLength);

    int main(int argc, char const *argv[])
    {
      int stringLength = 0;
      FILE *fp;         //Declaring a FILE type pointer calling it fp
      char buffer[64];  //Declaring a char array the size of 64 named buffer
      fp = fopen("./test.txt", "r");

      if (fp == NULL)
      {
        printf("File did not open\n");
        return 0;
      }
      else
      {
        while(fgets(buffer, 64, (FILE*)fp) != NULL)
        {
          printf("\nNormal String:   %s", buffer); //Print content in buffer(original array)
          stringLength = strlen(buffer);           //Storing the length of read input

          char reverse[stringLength + 1];

          reversing(buffer, reverse, stringLength);
          printf("Reversed String: %s\n", reverse);//Print content in reverse(Reverse array)
        }

      printf("\nEND OF FILE Reached!\n");
     }
     fclose(fp);
     return 0;
   }

  void reversing(char buffer[], char reverse[], int stringLength)
  {
    int i = 0;
    int j = stringLength - 1;
    while(i < stringLength)
    {
      reverse[j] = buffer[i]; //Swap elements
      i++;
      j--;
    }
    reverse[i] = '\0'; //Add null terminating 

    i = 0;
    if(reverse[0] == '\n') //If first element is '\n' swift elements
    {
       while(i < stringLength)
       {
        reverse[i] = reverse[i + 1];
        i++;
       }
    }
  }

现在打印到屏幕

    Normal String:   A
    Reversed String: A

    Normal String:   AB
    Reversed String: BA

    Normal String:   ABC
    Reversed String: CBA

    Normal String:   ABCD
    Reversed String: DCBA

    Normal String:   ABCDE
    Reversed String: EDCBA

    END OF FILE Reached!

感谢@PhantomWhiskers和所有评论并提供原始问题解决方案的人。

在从C中的文件读取输入时反转数组的麻烦

4 个答案: