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Concepts

For this project, we expect you to look at this concept:

Resources

Read or watch:

man or help:

  • ar
  • ranlib
  • nm

Additional Resource

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 is a static library, how does it work, how to create one, and how to use it
  • Basic usage of ar, ranlib, nm

Requirements

C

  • 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
  • You are not allowed to use the standard library. Any use of functions like printf, puts, 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

Bash

  • Allowed editors: vi, vim, emacs
  • All your scripts will be tested on Ubuntu 20.04 LTS
  • All your files should end with a new line (why?)
  • The first line of all your files should be exactly #!/bin/bash
  • A README.md file, at the root of the folder of the project, describing what each script is doing
  • All your files must be executable

More Info

You do not need to learn about dynamic libraries, yet.

Quiz questions

Question #0

What command is used to create a static library from object files?

  • nm

  • gcc

  • ld

  • ar

  • ranlib

Question #1

What is the format of a static library?

  • An archive

  • A relocatable ELF file

  • An executable ELF file

  • A shared ELF file

Question #2

What is the point of using ranlib?

  • List the content of a library

  • Creating an archive

  • Indexing an archive

  • Create a library from a simple archive

Question #3

What command(s) can be used to list the symbols stored in a static library?

  • ld

  • nm

  • ranlib

  • ar

Tasks

0. A library is not a luxury but one of the necessities of life

Create the static library libmy.a containing all the functions listed below:

int _putchar(char c);
int _islower(int c);
int _isalpha(int c);
int _abs(int n);
int _isupper(int c);
int _isdigit(int c);
int _strlen(char *s);
void _puts(char *s);
char *_strcpy(char *dest, char *src);
int _atoi(char *s);
char *_strcat(char *dest, char *src);
char *_strncat(char *dest, char *src, int n);
char *_strncpy(char *dest, char *src, int n);
int _strcmp(char *s1, char *s2);
char *_memset(char *s, char b, unsigned int n);
char *_memcpy(char *dest, char *src, unsigned int n);
char *_strchr(char *s, char c);
unsigned int _strspn(char *s, char *accept);
char *_strpbrk(char *s, char *accept);
char *_strstr(char *haystack, char *needle);

If you haven’t coded all of the above functions create empty ones with the right prototype. Don’t forget to push your main.h file to your repository. It should at least contain all the prototypes of the above functions.

julien@ubuntu:~/0x09. Static Librairies$ ar -t libmy.a
0-isupper.o
0-memset.o
0-strcat.o
1-isdigit.o
1-memcpy.o
1-strncat.o
100-atoi.o
2-strchr.o
2-strlen.o
2-strncpy.o
3-islower.o
3-puts.o
3-strcmp.o
3-strspn.o
4-isalpha.o
4-strpbrk.o
5-strstr.o
6-abs.o
9-strcpy.o
_putchar.o
julien@ubuntu:~/0x09. Static Librairies$ nm libmy.a

0-isupper.o:
0000000000000000 T _isupper

0-memset.o:
0000000000000000 T _memset

0-strcat.o:
0000000000000000 T _strcat

1-isdigit.o:
0000000000000000 T _isdigit

1-memcpy.o:
0000000000000000 T _memcpy

1-strncat.o:
0000000000000000 T _strncat

100-atoi.o:
0000000000000000 T _atoi

2-strchr.o:
0000000000000000 T _strchr

2-strlen.o:
0000000000000000 T _strlen

2-strncpy.o:
0000000000000000 T _strncpy

3-islower.o:
0000000000000000 T _islower

3-puts.o:
                 U _putchar
0000000000000000 T _puts

3-strcmp.o:
0000000000000000 T _strcmp

3-strspn.o:
0000000000000000 T _strspn

4-isalpha.o:
0000000000000000 T _isalpha

4-strpbrk.o:
0000000000000000 T _strpbrk

5-strstr.o:
0000000000000000 T _strstr

6-abs.o:
0000000000000000 T _abs

9-strcpy.o:
0000000000000000 T _strcpy

_putchar.o:
0000000000000000 T _putchar
                 U write
julien@ubuntu:~/0x09. Static Librairies$ cat main.c
#include "main.h"

int main(void)
{
    _puts("\"At the end of the day, my goal was to be the best hacker\"\n\t- Kevin Mitnick");
    return (0);
}
julien@ubuntu:~/0x09. Static Librairies$ gcc -std=gnu89 main.c -L. -lmy -o quote
julien@ubuntu:~/0x09. Static Librairies$ ./quote
"At the end of the day, my goal was to be the best hacker"
    - Kevin Mitnick
julien@ubuntu:~/0x09. Static Librairies$

Repo:

  • GitHub repository: alx-low_level_programming
  • Directory: 0x09-static_libraries
  • File: libmy.a, main.h

1. Without libraries what have we? We have no past and no future

Create a script called create_static_lib.sh that creates a static library called liball.a from all the .c files that are in the current directory.

julien@ubuntu:~/0x09. Static Librairies$ ls *.c
0-isupper.c  0-strcat.c  1-isdigit.c  1-strncat.c  2-strlen.c   3-islower.c  3-strcmp.c  4-isalpha.c  5-strstr.c  9-strcpy.c  _putchar.c
0-memset.c   100-atoi.c  1-memcpy.c   2-strchr.c   2-strncpy.c  3-puts.c     3-strspn.c  4-strpbrk.c  6-abs.c
julien@ubuntu:~/0x09. Static Librairies$ ./create_static_lib.sh
julien@ubuntu:~/0x09. Static Librairies$ ls *.a
liball.a
julien@ubuntu:~/0x09. Static Librairies$ ar -t liball.a
0-isupper.o
0-memset.o
0-strcat.o
100-atoi.o
1-isdigit.o
1-memcpy.o
1-strncat.o
2-strchr.o
2-strlen.o
2-strncpy.o
3-islower.o
3-puts.o
3-strcmp.o
3-strspn.o
4-isalpha.o
4-strpbrk.o
5-strstr.o
6-abs.o
9-strcpy.o
_putchar.o
julien@ubuntu:~/0x09. Static Librairies$

Repo:

  • GitHub repository: alx-low_level_programming
  • Directory: 0x09-static_libraries
  • File: create_static_lib.sh