Lecture 01

Question 1

What is POSIX?

Answer 1

A standard that attempts to define a common API across operating systems.

Question 2

Which of the following OSes is not POSIX compliant?
Linux
Windows
MacOS

Answer 2

Windows.

Of course it’s fucking Windows.

Question 3

What unix command is used to access the manual page for a given tool or library?

Answer 3

man

Question 4

What is the function prototype for the function ‘open’?

Answer 4

int open(const char* pathname, int flags);

Question 5

What different values can be passed as flags to the open() function?

Answer 5

O_RDONLY
O_WRONLY
O_RDWR
O_TRUNC
O_CREAT

Question 6

What is the function prototype for read()?

Answer 6

ssize_t(int fd, void *buf, size_t count);

Question 7

Why does read() return a ssize_t and not a size_t?

What’s the difference?

Answer 7

A ssize_t is a signed size_t.

read uses this so it can return -1 in the event of an error.

Question 8

What function can be used to create a new file?

Answer 8

creat

Question 9

What is the function prototype for creat?

Answer 9

int creat(const char* pathname, mode_t mode);

Question 10

What stream number is stdin?

Answer 10

0

Question 11

What stream number is stdout?

Answer 11

1

Question 12

What stream number is stderr?

Answer 12

2

Question 13

What is the function prototype for lseek?

Answer 13

off_t lseek(int fildes, off_t offset, int whence);

Question 14

What does lseek do when whence is equal to ‘SEEK_SET’?

Answer 14

Sets the position to offset bytes from the start of the file.

Question 15

What does lseek do when whence is equal to ‘SEEK_CUR’?

Answer 15

Sets the position to the current position plus offset bytes.

Question 16

What does lseek do when whence is equal to ‘SEEK_END’?

Answer 16

Sets the position to the size of the file plus offset bytes.

Question 17

What happens to the file size when you lseek using ‘SEEK_END’ and an offset >= 1?

Answer 17

The file size gets bigger.

Question 18

What is the function prototype for fread?

Answer 18

size_t fread(void ptr, size_t size, size_t nmemb, FILE stream);

Question 19

What is the function prototype for fwrite?

Answer 19

size_t fwrite(const void ptr, size_t size, size_t nmemb, FILE stream);

Question 20

What is the function prototype for fseek?

Answer 20

int fseek(FILE* stream, long offset, int whence);