[\<- Notes 01/31](01-31.md)

---

# Arrays of Linked Lists

- Linked Lists can be initialized as follow:

```
#define NODE struct node

struct node{
	char name[20];
	int size;
	NODE *next;
};

struct list{
	NODE *head;
	NODE *tail;
};

struct list x[4];
```

- Now you have 4 linked lists in `x`, each with a head and tail
- Inserting and deleting should be the same, just specify which element in the `x` array you are inserting/deleting

---

# Files

- Two kinds of files we will cover:

## Text Files

- Colletions of characters saved in a secondary storage
- No fixed size
- End file with `<eof>`
- End of lines are marked with `('\n')`

Example:

```
This is a text file!<newline>
It has two lines.<newline><eof>
```

The actual file will look like this:

```
This is a text file!<newline>It has two lines.<newline><eof>
```

- All textual **input** and **output** data are actually a continuous **stream** of character codes
	- We refer to a data source or destinations as an **input stream** or an **output stream**
	- These general terms can be applied to:
		- files
		- the keyboard
		- the screen
		- any other source of input data or destinations of output data

- Keyboard and Screen
	- **stdin**
		- keyboard's input stream
	- **stdout**
		- "normal" output stream associated with the screen
	- **stderr**
		- "error" output stream associated with the screen
	- **Streams are treated like text files**
		- Their individual components are characters

- **To read from stdin**

```
r = scanf("%d", &num);
```
or
```
ch = getchar();
```

- **The characters are read sequentially**
	- Consecutive calls to scanf and/or getchar will read **consecutive elements** from the keyboard
	- ^D usually represents `<eof>`

- **scanf**
	- Returns how many elements were read
	- Placeholders define the type
	
	- Examples:

```
%c, %d, %f, %s
```

	- **For limiting the size of a string**
		- %Ns - reads up to N characters (array size should be N+1)
	- **For lines**

```
r = scanf("%[^'\n']", string_name);
```

	- Only reads the characters as specified by the placeholder
		- Spacers (\n, \t, or spaces) may be left in the buffer from previous calls
	- **To clear buffer:**
		- fpurge() - erases any input or output buffered in the given stream
		- Example:

```
fpurge(stdin);
r = scanf("%[^'\n']", string_name);
```

- **To read lines**
	- fgets(array, SIZE, stdin);
		- Includes the \n at the end of the line
		- If used after scanf, may need to clear the buffer

- **To write to stdout**
	- `printf("%d", num);` or `putchar(ch);`

- **The file is written sequentially**
	- Consecutive calls to `printf` and/or `putchar` will write **consecutive elements** to the file

## Working with Text Files

```
FILE *infp

if((infp = fopen("data.txt", "r")) == NULL) printf("cannot open the file dat.txt\n"); //failsafe
```

- The file is always open for reading from the beginning

- To open a text file for reading when the **name is stored in a string:**

```
char file_name[50];
FILE *infp;

if((infp = fopen(file_name, "r")) == NULL) printf("cannot open");
```

- **To read from the text file**

```
ret = fscanf(infp, "%d", &num);
```
or
```
ch = getc(infp);
```

- The file is read **sequentially**
- **Returned value**
	- fscanf -- number of values converted 
	- getc -- the character read (returns EOF at end of file)

- Open a text file for writing from the **beginning**:

```
char file_name[50];
FILE *outfp;

if((outfp = fopen(file_name, "w")) == NULL) printf("Cannot open the file %s\n", file_name);
```

- Open a text file for writing from the **end**:
	
```
char file_name[50];
FILE *outfp;

if((outfp = fopen(file_name, "a")) == NULL) printf("cannot open the file %s\n", file_name);
```

- To **Write** to a text file:

```
fprintf(outfp, "%d", num);
```
or
```
putc(ch, outfp);
```

- The file is written sequentially
	- Consecutive calls to fprintf and/or putc will write consecutive elements to the file

- To **Close** a text file:

```
fclose(infp);
fclose(outfp);
```

---

[-> Notes 02/10](02-10.md)