使用指针访问结构成员时的垃圾数据

Question

struct _StoryElement_ {
char *title_of_chapter_;
struct _StoryElement_ *path_a_;
struct _StoryElement_ *path_b_;
char *content_of_chapter_;
};
typedef struct _StoryElement_ StoryElement;

So I have a Tree of these Structs created each containing different values. I initialised them all using the following functions:

StoryElement *insertIntoStoryElement(StoryElement* root, char* title_of_chapter, char* content_of_chapter)
{
  if(root == NULL)
  {
    root = makeNewStoryElement(root, title_of_chapter, content_of_chapter);
  }
  else if (root->path_a_ == NULL)
  {
    root->path_a_ = makeNewStoryElement(root, title_of_chapter, content_of_chapter);
  }
  else if (root->path_b_ == NULL)
  {
    root->path_b_ = makeNewStoryElement(root, title_of_chapter, content_of_chapter);
  }

  return root;
}

StoryElement *makeNewStoryElement(StoryElement* root, char* title_of_chapter,
                                  char* content_of_chapter)
{
  root = (StoryElement*) malloc(sizeof(StoryElement));

  root->title_of_chapter_ =
  (char*)malloc(sizeof(char*)*(strlen(title_of_chapter) + 1));
  root->content_of_chapter_ =
  (char*)malloc(sizeof(char*)*(strlen(title_of_chapter) + 1));

  //strcpy(NewStoryElement->title_of_chapter_, title_of_chapter);
  //strcpy(NewStoryElement->content_of_chapter_, content_of_chapter);
  title_of_chapter = root->title_of_chapter_;
  content_of_chapter = root->content_of_chapter_;

  root->path_a_ = NULL;
  root->path_b_ = NULL;

  return root;
}

This function is what provides me with the string values that I pass onto insertIntoStoryElement():

StoryElement *createStoryTree (StoryElement *root, char *storage)
{

  char* pos = storage;
  pos = strchr(pos, '\n');
  *pos = '\0';
  int size = strlen(storage);
  char* title = malloc(size + 1);
  strcpy(title, storage);

  char* ptr_path_a = pos + 1;
  pos = strchr(ptr_path_a, '\n');
  *pos = '\0';
  size = strlen(ptr_path_a);
  char* path_a = malloc(size + 1);
  strcpy(path_a, ptr_path_a);

  char* ptr_path_b = pos + 1;
  pos = strchr(ptr_path_b, '\n');
  *pos = '\0';
  size = strlen(ptr_path_b);
  char* path_b = malloc(size + 1);
  strcpy(path_b, ptr_path_b);

  char* ptr_text = pos + 1;
  pos = strchr(pos + 1, '\0');
  *pos = '\0';
  size = strlen(ptr_text);
  char* text = malloc(size + 1);
  strcpy(text, ptr_text);

  root = insertIntoStoryElement(root, title, text);

/*  if(strcmp(path_a, "-")!=0 && strcmp(path_b, "-")!=0)
  {*/
    root->path_a_ = readStoryFromFile(root->path_a_, path_a);
    root->path_a_ = readStoryFromFile(root->path_b_, path_b);
  //}

  return root;
}

And this is the function that is ultimately called in main:

StoryElement *readStoryFromFile (StoryElement *root, char *filename)
{
  if(strcmp(filename, "-") == 0)
  {
    //printf("End  reached\n");
    return 0;
  }
  FILE *file = fopen(filename, "r");

    if(!file)
  {
    printf("[ERR] Could not read file %s.\n", filename);
    return 0;
  }

  long fsize = getFileSize(file);

  char* storage = malloc(fsize + 1);
  if(!storage)
  {
    printf("[ERR] Out of memory.\n");
    return 0;
  }

  fread(storage, fsize, 1, file);
  storage[fsize] = '\0';
  fclose(file);

  root = createStoryTree(root, storage);

  free(storage);

  return root;
}

And this is my main which uses another function but only the 2 above are relevant for this question I think:

int main ( int argc, char *argv[] )
{
  if ( argc != 2 ) /* argc should be 2 for correct execution */
  {
    printf( "Usage: ./ass2 [file-name]\n");
    return (1);
  }

  StoryElement *root = NULL;

  root = readStoryFromFile(root, argv[1]);
  if(!root)
    return 3;

  printf("%p\n", root);
  printf("%s\n", root->title_of_chapter_);

  //printStoryTree(root);
  freeStoryTree(root);

  root = NULL;

  return 0;
}

And finally my problem is that the 2 printfs after in the main function return the following: First pointer Address is ok I think, but the second printf should be "Kapitel_1.txt" Why am I getting a garbage value here? Is this a segmentation fault?

Answer 1

In your function makeNewStoryElement you malloc the space for root->title_of_chapter but you don't put the content of the given title_of_chapter in it. This means that root->title_of_chapter will contain whatever garbage data was in the location you got back from the malloc.
Do something like strcpy(root->title_of_chapter, title_of_chapter);
the printf will then be fine.
The code has some other problems and things you shouldn't do but this should fix the problem that you are asking about.