Preprocessor

Question 1

What does the following do?

1. # include
2. # include “filename”
3. # define name [value]

Answer 1

1. Insert a library file’s contents into this file. Compier looks in default search path
2. insert a user file’s contents into this file - directive causes the contents of a specified file to be included in a program. AKA headerfiles, include files. Compiler searches for the file in the current directory
3. Creates a preprocessor symbol (“variable”) - defines a macro.

Question 2

How does the preprocessor work?

Answer 2

The input is a C program (possibly containing directives). The preprocessor executes these directives, removing them in the process. The preprocessor’s output goes directly into the compiler

Question 3

How do you have the compiler use the debug command and how does the code work in the program?

Answer 3

ifdef Debug

clang -DDEBUG

examples:

//debug only code

//production code

Question 4

How do you define a const?

Answer 4

const int = 4;

Question 5

how do you define a typedef?

Answer 5

typedef float dollars;

now float and dollars are interchangable

Question 6

What are the compiling steps for the preprocessor?

Answer 6

Step 1: C program -> [Preprocessor] -> Modified C program (literally copied in)

Step 2: Modified C program ->[Compiler]-> object code

Question 7

What are the 3 types of preprocessing directives

Answer 7

1. Macros
2. File Inclusion
3. Conditionals

Question 8

What are 2 ways macros can be used?

Answer 8

1. To define a constant (#DEFINE THENUM 1)
2. Like a function (see image)

Question 9

How are conditionals used?

Answer 9

if (statement)

code runs

It is important to note, variables must be #define constants to use them in the statements