CODEWITHSUNDEEP
cfile-copying
krystalgamer
krystalgamer

Reputation: 150

Why this way of copying files isn't working

I'm writing a wrapper to help me in my future projects (I finished C book), and want to copy a file without using fgetc. Here's my code, it doesn't work:

int CopyFile(char* filename, char* dest)
{
  FILE* fp, *fout;
  fp = fopen(filename,"rb");
  //fout = fopen(dest, "wb");
  if(fp == NULL)
  {
    return -1;
  }
  /*while((c = fgetc(fp)) != EOF)
  {
    fputc(c,fout);
  }*/
  long size = GetFileSize(fp);
  printf("%lu", size);
  char* file = malloc(size);
  fread(file, size, 1, fp);
  //fclose(fp);
  fout = fopen(dest, "wb");
  fwrite(file, size, 1, fout);
  fclose(fp);
  fclose(fout);
  return 0;

}

I even open the files with a hexeditor and they aren't similar. What am I doing wrong?

Upvotes: 0

Views: 243

Answers (1)

Some programmer dude
Some programmer dude

Reputation: 409176

The problem is in the GetFileSize function, where you move the file-pointer to the end, but you never rewind to the beginning again.

That means your fread function call will not actually read anything, as the pointer already is at the end of the file. So what's written is the contents of the allocated memory, which is indeterminate (and will be seemingly random).

If you checked what fread returned, you would have seen this immediately.

Let this be a lesson on always checking the return values of functions which can fail in one way or the other.

Upvotes: 3

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