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Resources

Read or watch:

Learning Objectives

At the end of this project, you are expected to be able to explain to anyone, without the help of Google:

General

  • What are macros and how to use them
  • What are the most common predefined macros
  • How to include guard your header files

Requirements

General

  • Allowed editors: vi, vim, emacs
  • All your files will be compiled on Ubuntu 20.04 LTS using gcc, using the options -Wall -Werror -Wextra -pedantic -std=gnu89
  • All your files should end with a new line
  • A README.md file, at the root of the folder of the project is mandatory
  • Your code should use the Betty style. It will be checked using betty-style.pl and betty-doc.pl
  • You are not allowed to use global variables
  • No more than 5 functions per file
  • The only C standard library functions allowed are malloc, free and exit. Any use of functions like printf, puts, calloc, realloc etc… is forbidden
  • You are allowed to use _putchar
  • You don’t have to push _putchar.c, we will use our file. If you do it won’t be taken into account
  • In the following examples, the main.c files are shown as examples. You can use them to test your functions, but you don’t have to push them to your repo (if you do we won’t take them into account). We will use our own main.c files at compilation. Our main.c files might be different from the one shown in the examples
  • The prototypes of all your functions and the prototype of the function _putchar should be included in your header file called main.h
  • Don’t forget to push your header file
  • All your header files should be include guarded

Quiz questions

Question #0

Why should we use include guards in our header files?

  • To avoid the problem of double inclusion when dealing with the include directive.

  • Because we said so, and we should never ask why.

Question #1

This is the correct way to define the macro SUB:

#define SUB(a, b) a - b
  • No, it should be written this way:
#define SUB(a, b) ((a) - (b))

  • Yes

  • No, it should be written this way:

#define SUB(a, b) (a - b)
  • No, it should be written this way:
#define SUB(a, b) (a) - (b)

Question #2

NULL is a macro

  • False

  • True

Question #3

What will be the last 5 lines of the output of the command gcc -E on this code?

#include <stdlib.h>

int main(void)
{
    NULL;
    return (EXIT_SUCCESS);
}

Choose:

int main(void)
{
 '\0';
 return (0);
}
int main(void)
{
 0;
 return (0);
}
int main()
{
 0;
 return (0);
}
int main(void)
{
 ((void *)0);
 return (0);
}

Question #4

The macro __FILE__ expands to the name of the current input file, in the form of a C string constant.

  • False

  • True

Question #5

What are the steps of compilation?

  • compiler 2. preprocessor 3. assembler 4. linker

  • preprocessor 2.compiler 3. assembler 4. linker

  • preprocessor 2.compiler 3. linker 4. assembler

Question #6

The preprocessor links our code with libraries.

  • False

  • True

Question #7

The preprocessor generates assembly code

  • False

  • True

Question #8

This code will try to allocate 1024 bytes in the heap:

#define BUFFER_SIZE 1024
malloc(BUFFER_SIZE)

  • False

  • True

Question #9

The preprocessor generates object code

  • False

  • True

Question #10

This portion of code is actually using the library stdlib.

#include <stdlib.h>

  • False

  • True

Question #11

What is the gcc option that runs only the preprocessor?

  • -preprocessor

  • -a

  • -cisfun

  • -P

  • -E

  • -pedantic

  • -p

Question #12

The preprocessor removes all comments

  • False

  • True

Question #13

What will be the output of this program? (on a standard 64 bits, Linux machine)

#include <stdio.h>
#include <stdlib.h>

#define int char

int main(void)
{
    int i;

    i = 5;
    printf ("sizeof(i) = %lu", sizeof(i));
    return (EXIT_SUCCESS);
}

  • sizeof(i) = 1

  • sizeof(i) = 4

  • Segmentation Fault

  • It does not compile

  • sizeof(i) = 5

  • sizeof(i) = 8

Question #14

What does the macro TABLESIZE expand to?

#define BUFSIZE 1020
#define TABLESIZE BUFSIZE
#undef BUFSIZE
#define BUFSIZE 37

  • 1020

  • 37

  • nothing

Tasks

0. Object-like Macro

Create a header file that defines a macro named SIZE as an abbreviation for the token 1024.

julien@ubuntu:~/0x0c. macro, structures$ cat 0-main.c
#include "0-object_like_macro.h"
#include "0-object_like_macro.h"
#include <stdio.h>

/**
 * main - check the code
 *
 * Return: Always 0.
 */
int main(void)
{
    int s;

    s = 98 + SIZE;
    printf("%d\n", s);
    return (0);
}
julien@ubuntu:~/0x0c. macro, structures$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 0-main.c -o a
julien@ubuntu:~/0x0c. macro, structures$ ./a
1122
julien@ubuntu:~/0x0c. macro, structures$

Repo:

  • GitHub repository: alx-low_level_programming
  • Directory: 0x0D-preprocessor
  • File: 0-object_like_macro.h

1. Pi

Create a header file that defines a macro named PI as an abbreviation for the token 3.14159265359.

julien@ubuntu:~/0x0c. macro, structures$ cat 1-main.c
#include "1-pi.h"
#include "1-pi.h"
#include <stdio.h>

/**
 * main - check the code
 *
 * Return: Always 0.
 */
int main(void)
{
    float a;
    float r;

    r = 98;
    a = PI * r * r;
    printf("%.3f\n", a);
    return (0);
}
julien@ubuntu:~/0x0c. macro, structures$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 1-main.c -o b
julien@ubuntu:~/0x0c. macro, structures$ ./b
30171.855
julien@ubuntu:~/0x0c. macro, structures$

Repo:

  • GitHub repository: alx-low_level_programming
  • Directory: 0x0D-preprocessor
  • File: 1-pi.h

2. File name

Write a program that prints the name of the file it was compiled from, followed by a new line.

  • You are allowed to use the standard library
julien@ubuntu:~/0x0c. macro, structures$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 2-main.c -o c
julien@ubuntu:~/0x0c. macro, structures$ ./c
2-main.c
julien@ubuntu:~/0x0c. macro, structures$ cp 2-main.c 02-main.c
julien@ubuntu:~/0x0c. macro, structures$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 02-main.c -o cc
julien@ubuntu:~/0x0c. macro, structures$ ./cc
02-main.c
julien@ubuntu:~/0x0c. macro, structures$

Repo:

  • GitHub repository: alx-low_level_programming
  • Directory: 0x0D-preprocessor
  • File: 2-main.c

3. Function-like macro

Write a function-like macro ABS(x) that computes the absolute value of a number x.

julien@ubuntu:~/0x0c. macro, structures$ cat 3-main.c
#include <stdio.h>
#include "3-function_like_macro.h"
#include "3-function_like_macro.h"

/**
 * main - check the code
 *
 * Return: Always 0.
 */
int main(void)
{
    int i;
    int j;

    i = ABS(-98) * 10;
    j = ABS(98) * 10;
    printf("%d, %d\n", i, j);
    return (0);
}
julien@ubuntu:~/0x0c. macro, structures$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 3-main.c -o d
julien@ubuntu:~/0x0c. macro, structures$ ./d
980, 980
julien@ubuntu:~/0x0c. macro, structures$

Repo:

  • GitHub repository: alx-low_level_programming
  • Directory: 0x0D-preprocessor
  • File: 3-function_like_macro.h

4. SUM

Write a function-like macro SUM(x, y) that computes the sum of the numbers x and y.

julien@ubuntu:~/0x0c. macro, structures$ cat 4-main.c
#include <stdio.h>
#include "4-sum.h"
#include "4-sum.h"

/**
 * main - check the code
 *
 * Return: Always 0.
 */
int main(void)
{
    int s;

    s = SUM(98, 1024);
    printf("%d\n", s);
    return (0);
}
julien@ubuntu:~/0x0c. macro, structures$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 4-main.c -o e
julien@ubuntu:~/0x0c. macro, structures$ ./e
1122
julien@ubuntu:~/0x0c. macro, structures$

Repo:

  • GitHub repository: alx-low_level_programming
  • Directory: 0x0D-preprocessor
  • File: 4-sum.h