Week 9

Question 1

There are two main ways the compile views a 2d array, how do they differ?

Answer 1

int a[][] is a cube

int **b is an array with each array item pointing to another array

Question 2

How many malloc calls do we require to create a 2D array?

Answer 2

Two mallocs

Question 3

How do you interpret the declaration int ***a?

Answer 3

A 3D array

A pass-by-reference of a 2D array

Question 4

Given int **a: What data type if a?

Answer 4

A is a 2D array or a pass-by-reference of a 1D array

Question 5

Given int **a: What is *a?

Answer 5

A pointer to an integer

Question 6

Given int **a: What is **a?

Answer 6

**a is an integer value

Question 7

What are the three modes of interacting with files?

Answer 7

Read the contents of a file

Write to a new file

Append to an existing file

Question 8

Writing and appending operate in a similar manner. What is the main difference?

Answer 8

Where the writing happens.

Write -> start writing at the first byte of the file

Appending -> start writing after the last byte of the file

Question 9

If the file doesn’t exist when its called, what happens?

Answer 9

The open call fails

Question 10

What are the four buffers to your program?

Answer 10

Keyboard input

Screen output

disc drive output

network output

Question 11

Emptying a buffer: What is the input buffer?

Answer 11

Reading the data

Question 12

Emptying a buffer: What is the output buffer?

Answer 12

Filling the buffer
Printing \n (for the screen only)
Closing the file
Explicitly pushing the data to the file

Question 13

What is “flushing” the buffer?

Answer 13

Explicitly pushing the data to the file

Question 14

How are files accessed?

Answer 14

Through a file descriptor

Question 15

The file descriptor keeps track of all the important file information. What is it?

Answer 15

Where does the file live?
Where am in the file?
What operations are available on the file?
What permissions do I have for the file?

Question 16

Where do stdin, stdout and stderr exist?

Answer 16

In the open file table

Question 17

FILE *fopen(char *file_path, char *mode) opens a file. What are the options for mode?

Answer 17

r, w, a

r - open in read mode
w - open in write mode
a - open in append mode

Question 18

It’s rarely done, but adding a + to the mode allows what?

Answer 18

Both input and output

Question 19

What does char *fgets( char *buffer, int buffer_size, FILE *file_descriptor); do?

Answer 19

Returns the pointer to the buffer if data was read, NULL otherwise

Question 20

What does fscanf(FILE *file_descriptor, char *pattern, …); do?

Answer 20

Returns the number of items of the pattern matched

Question 21

What does int fgetc( FILE *file_descriptor); do?

Answer 21

Returns unsigned char promoted to an int

Question 22

What does int ungetc(int character, FILE *file_descriptor); do?

Answer 22

Put a read character back into the data buffer

Question 23

What does feof( FILE *file_descriptor) do?

Answer 23

Returns zero (false) if there is more data in the file to read

Question 24

What does int fprintf( FILE * file_descriptor, char *pattern, …); do?

Answer 24

Returns the number of bytes printed.

Question 25

What does fputs( char *string, FILE *file_descriptor) do?

Answer 25

Returns the number of characters printed

Question 26

What does fputc( int character, FILE *file_descriptor) do?

Answer 26

Returns the character printed or EOF

Question 27

What does fflush( FILE *file_descriptor) do?

Answer 27

Flush the data from the buffer to the IO device

Returns 0 if the flush was successful

Question 28

What does char *tmpname( char *name_buffer) do?

Answer 28

Get the name of the temporary file that you can open

Typically appears in the /tmp directory

The name is stored in name_buffer
Must have at least L_tmpnam butes in the array

Returns name_buffer if successful, NULL otherwise

Question 29

What does FILE *tmpfile( void) do?

Answer 29

Open a temporary file

You won’t know the file name

Opened in w+ mode, so you can read or write to it