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[\<- 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)
|
