Week 12

Question 1

What does the c preprocessor do?

Answer 1

Makes changes to your program before code generation begins

Question 2

What are the typical uses of a c preprocessor?

Answer 2

Including other files like .h files

Defining constants

Defining macros

Selectively include or exclude some parts of a program

Give additional details to the compiler

Question 3

What do all preprocessor commands begin with?

Answer 3

#

Question 4

What does #include do?

Answer 4

Include the contents of one file directly into another file

Question 5

What does #define symbol value do?

Answer 5

Replace all occurences of symbol with the value

Question 6

What does #define do?

Answer 6

Can be used to make macros with parameters

The don’t fully behave like function calls

Question 7

Is it a good practice to hae parameters in parantheses?

Answer 7

Yes, it helps to make sure we get the result we expected.

Question 8

What does FILE do?

Answer 8

the name of the file being compiled

Question 9

What is LINE?

Answer 9

The line number where symbol was found.

Question 10

What is DATE and TIME

Answer 10

indicates when the compilation happened

Question 11

What is FILE and LINE

Answer 11

Would most typically be used in other macros where you dn’t know immediately where the macro is being used.

Question 12

What do #if, #else, #endif do?

Answer 12

LEts you use an expression to determine what to include in a compilation

Exclude temporary code with #if 0 …#endif

Include OS-specific code based on the expression

Question 13

What is the shorthand for #if defined(X)…#endif

Answer 13

Becomes #ifdef X….#endif

Question 14

What is the shorthand for #if_defined(x)…#endif

Answer 14

Becomes #ifndef X ….#endif

Question 15

How are compiler specific commands defined?

Answer 15

by #pragma statements

Question 16

What do #error and #warning do?

Answer 16

Lets you print messages at compile time

Question 17

What is the set L?

Answer 17

Called the language

Question 18

What are the elements of Chomsky Hierarchy?

Answer 18

Different levels of complexity for matching patterns of data.

Regular expressions
Context-free grammars
Context-sensitive grammars
Unrestricted grammars

Question 19

What are the elements of regular expressions?

Answer 19

Simplest of rules

Cannot match the numbe of pairs of things like matching parantheses

Can be handled by finite state machine

Question 20

What are the elements of context-free grammars?

Answer 20

Needs a non-deterministic pushdown automaton

Question 21

What are the elements of context-sensitive grammars?

Answer 21

Needs a non-deterministic Turing machine

Question 22

What are the elements of the unrestricted grammars?

Answer 22

Allows for the most complx rules

Question 23

What are some different symbols to represent the regular expressions in different tools?

Answer 23

Grep, sed

bash pathname expansion, find

perl

Question 24

Grep/sed syntax: What are the basic operations?

Answer 24

Character specification

Catenation

Repetition

Grouping

Alternation

Question 25

What is catenation?

Answer 25

The step of putting two strings or patterns in sequence to make a longer string or pattern.

Question 26

Does order of catenation matter?

Answer 26

Yes

Question 27

What are the repetition notation of grep/sed repetition?

Answer 27

• matches 0 or more instances of the preceding character

+matches 1 or more instances of the preceding character

? Matches 0 or 1 instances of the preceding character

{n} matches n instances of the preceding character

{n,} matches n or more instances of the preceding character

{n,m} matches at least n and at most m instances of the preceding character

Question 28

If the catenation ab+ is used, what letter is affected?

Answer 28

asks for repetition of b, but not a

Question 29

What is egrep most commonly used for?

Answer 29

Most commonly used to apply repetition to a catenation

Question 30

How are alternatives separated in egrep/sed alternation?

Answer 30

by using the |

a|b|c| equivalent to [abcd]

Question 31

Are regex’s a part of standard c?

Answer 31

No, you just need to know that they’re available as the GNU posix regular expression library: regex.h

Question 32

What are the three steps to using the regular expressions?

Answer 32

1) Compile the expression into something usable with regcomp()
2) Use the compiled expression against 1 or more strings with regexec()
3) Release the compiled expression with regfree()

Question 33

What is regex_t?

Answer 33

The compiled pattern

Question 34

What are the two fields of regmatch_t?

Answer 34

rm_so - starting index of match

rm_eo - ending index of match