c - 从键盘读取文件名

Question

基本上，在下面的代码中，我尝试从键盘读取文件名(即 input.txt 和 output.txt)，但出现“段错误”。该程序还将小写字母转换为大写字母，并将大写字母转换为小写字母。有什么建议么？我究竟做错了什么？

#include <stdio.h>
#include <ctype.h>
#include <string.h>
int main() 
{

  char c;
  int charToLowerCase = 0;
  int charToUpperCase = 0;
  int countCharacters = 0;
  FILE *in_file = NULL;
  FILE *out_file = NULL;
  char str_in[100];
  char str_out[100];
  char *s_in = NULL;
  char *s_out = NULL;

  gets(str_in);
  gets(str_out);

  if (s_in != NULL)
   in_file = fopen(str_in, "r");

  if (s_out != NULL)
   out_file = fopen(str_out, "w");

  c = fgetc(in_file);
  while (c != EOF)
  {
    if (c >= 'A' && c <= 'Z')
    {
     fprintf(out_file, "%c", tolower(c));
     charToLowerCase++;
    }
    else if (c >= 'a' && c <= 'z')
           {
            fprintf(out_file, "%c", toupper(c));
            charToUpperCase++;
           }    
    else
     fprintf(out_file, "%c", c);

    c = fgetc(in_file);
    countCharacters++;
  }
  fprintf(out_file, "\n");
  fprintf(out_file, "Read %d characters in total, %d converted to upper-case, %d to lower-case.\n", countCharacters, charToUpperCase, charToLowerCase);

  fclose(in_file);
  fclose(out_file);
  return 0;
}

Answer 1

你想要这个:

int main() 
{
  int c;                        //<<< int instead of char
  int charToLowerCase = 0;
  int charToUpperCase = 0;
  int countCharacters = 0;
  FILE *in_file = NULL;
  FILE *out_file = NULL;
  char str_in[100];
  char str_out[100];

  gets(str_in);
  gets(str_out);

  in_file = fopen(str_in, "r");
  if (in_file == NULL)
  {
    // file could not be opened
    printf ("Could not open file %s\n", str_in);
    return 1;
  }

  out_file = fopen(str_out, "w");
  if (in_file == NULL)
  {
    // file could not be opened
    printf ("Could not open file %s\n", str_out);
    return 1;
  }

  ...