c - 文件的移位加密和解密 - 代码无法正常工作

Question

当我在代码块中运行它时，我的代码可以正常工作，但是当我尝试打开它的 .exe 文件时，它无法正常工作。请有人帮忙吗？

我是一名编程初学者。这是我正在编写的第一个代码。一个简单的 c 语言凯撒密码。我借助网络的帮助来编写代码。当我在代码块中运行它时，它运行良好，但当我运行 .exe 文件时，它不起作用。输入 key 后它就停止了。我现在不知道该怎么办。

#include <stdio.h>

#define MAXCHAR 1000

int main()
{
  int i, x, key;
  FILE *fptr;
  char str[MAXCHAR], ch, filename[MAXCHAR];

  printf("\nPlease enter a File Name: ");
  scanf("%s", &filename);
  fptr = fopen(filename, "r+");
  if (fptr == NULL){
    printf("Could not open file %s",filename);
  }
  while (fgets(str,MAXCHAR, fptr) != NULL);
  printf("\nPlease choose following options:\n");
  printf("1 = Encrypt the string.\n");
  printf("2 = Decrypt the string.\n");
  scanf("%d", &x);
  printf("Enter key: ");
  scanf("%d", &key);
  switch(x)
  {
  case 1:
    for(i = 0; str[i] != '\0'; ++i){
      ch = str[i];

      if(ch >= 'a' && ch <= 'z'){
        ch = ch + key;

        if(ch > 'z'){
          ch = ch - 'z' + 'a' - 1;
        }

        str[i] = ch;
      }
      else if(ch >= 'A' && ch <= 'Z'){
        ch = ch + key;

        if(ch > 'Z'){
          ch = ch - 'Z' + 'A' - 1;
        }

        str[i] = ch;
      }
    }
    printf("Encrypted string: %s\n", str);
    break;

  case 2:

    for(i = 0; str[i] != '\0'; ++i){
      ch = str[i];

      if(ch >= 'a' && ch <= 'z'){
        ch = ch - key;

        if(ch < 'a'){
          ch = ch + 'z' - 'a' + 1;
        }

        str[i] = ch;
      }
      else if(ch >= 'A' && ch <= 'Z'){
        ch = ch - key;

        if(ch < 'A'){
          ch = ch + 'Z' - 'A' + 1;
        }

        str[i] = ch;
      }
    }
    printf("Decrypted string: %s\n", str);
    break;

  default:
    printf("\nError\n");
  }

  return 0;
}

这是我试图满足的要求。

Implementation:

1. File encryption
2. File decryption

Note:

Read the contents(plain text) from a file (only English letter allowed) as characters, in terms of the KEY (input from keyboard by user ) shift the corresponding character(get cipher text), and do the reverse operation when decrypting the file.

For example:

Assume the plain text is “abcdef”, KEY is 5, then every single letter in the plain text will shift right by 5 positions according to the alphabet( the following letter after z is a), get the cipher text (garbled)“fghijkl”.

Now decrypt the cipher text: fghijkl, KEY is 5, and then every single letter in the cipher text will be shift left by 5 positions according to the alphabet( the following letter after a is z), get the original text “abcdef”.

Answer 1

您提到的代码几乎没有问题。首先这个

scanf("%s", &filename); /* & is not needed */

这是错误的，编译器可能会警告你

error: format ‘%s’ expects argument of type ‘char *’, but argument 2 has type ‘char (*)[1000]’ [-Werror=format=]

如果您使用 -Wall -Wstrict-prototypes -Werror 等标志编译代码。删除 & 因为 filename 是 char 数组和数组名称本身的地址，正确的是

scanf("%s", filename);

其次，这里

while (fgets(str,MAXCHAR, fptr) != NULL); /* dummy loop */

while 末尾的

分号 ; 是故意的还是拼写错误？由于 ; 当循环失败时 str 包含 NULL。你可能想要像

while (fgets(str,MAXCHAR, fptr) != NULL) { /* some code */ }

此外，fgets() 将新行存储在缓冲区末尾，您可能需要删除尾随的 \n。例如

while(fgets(str, MAXCHAR, fptr) != NULL) {
        str[strcspn(str, "\n")] = 0; /* remove the trailing \n */
        /* some code */
 }

最后来了

if (fptr == NULL){
    printf("Could not open file %s",filename);
  }

fopen() 处理不正确，就好像文件不存在或 fopen() 失败一样，它只是打印消息并进一步继续并使用 fptr 不应该使用，请使用 return 0 或 exit(0)。例如

if (fptr == NULL){
    fprintf(stderr,"Could not open file %s",filename);
    return 0; /* this is must */
}

示例代码:

#define MAXCHAR 1000
int main(void) {
        int i, x, key;
        FILE *fptr;
        char str[MAXCHAR], ch, filename[MAXCHAR]/* I don't think filename will be that much big, use accordingly */;
        printf("\nPlease enter a File Name: ");
        scanf("%s", &filename); /* & is not required as filename itself address */
        fptr = fopen(filename, "r+");
        if (fptr == NULL){
                printf("Could not open file %s",filename);
                return 0; /* add this else it proceeed further */
        }
        while (fgets(str,MAXCHAR, fptr) != NULL) { /* remove semicolon, read each line from file, store into str and do the operation with str  */
                printf("\nPlease choose following options:\n");
                printf("1 = Encrypt the string.\n");
                printf("2 = Decrypt the string.\n");
                scanf("%d", &x);
                printf("Enter key: ");
                scanf("%d", &key);
                switch(x) {
                        case 1:
                                for(i = 0; str[i] != '\0'; ++i){
                                        ch = str[i];

                                        if(ch >= 'a' && ch <= 'z'){
                                                ch = ch + key;
                                                if(ch > 'z'){
                                                        ch = ch - 'z' + 'a' - 1;
                                                }

                                                str[i] = ch;
                                        }
                                        else if(ch >= 'A' && ch <= 'Z'){
                                                ch = ch + key;
                                                if(ch > 'Z'){
                                                        ch = ch - 'Z' + 'A' - 1;
                                                }

                                                str[i] = ch;
                                        }
                                }
                                printf("Encrypted string: %s\n", str);
                                break;
                        case 2:
                                for(i = 0; str[i] != '\0'; ++i){
                                        ch = str[i];
                                        if(ch >= 'a' && ch <= 'z'){
                                                ch = ch - key;
                                                if(ch < 'a'){
                                                        ch = ch + 'z' - 'a' + 1;
                                                }

                                                str[i] = ch;
                                        }
                                        else if(ch >= 'A' && ch <= 'Z'){
                                                ch = ch - key;

                                                if(ch < 'A'){
                                                        ch = ch + 'Z' - 'A' + 1;
                                                }

                                                str[i] = ch;
                                        }
                                }
                                printf("Decrypted string: %s\n", str);
                                break;

                        default:
                                printf("\nError\n");

                }
        }
        return 0;
}