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README.md

0x00. C - Hello, World

  • By Julien Barbier

Resources

Read or watch:

man or help:

  • gcc
  • printf (3)
  • puts
  • putchar

Learning Objectives

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

General

  • Why C programming is awesome
  • Who invented C
  • Who are Dennis Ritchie, Brian Kernighan and Linus Torvalds
  • What happens when you type gcc main.c
  • What is an entry point
  • What is main
  • How to print text using printf, puts and putchar
  • How to get the size of a specific type using the unary operator sizeof
  • How to compile using gcc
  • What is the default program name when compiling with gcc
  • What is the official C coding style and how to check your code with betty-style
  • How to find the right header to include in your source code when using a standard library function
  • How does the main function influence the return value of the program

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 repo, containing a description of the repository
  • A README.md file, at the root of the folder of this project, containing a description of the project
  • There should be no errors and no warnings during compilation
  • You are not allowed to use system
  • Your code should use the Betty style. It will be checked using betty-style.pl and betty-doc.pl

Shell Scripts

  • Allowed editors: vi, vim, emacs
  • All your scripts will be tested on Ubuntu 20.04 LTS
  • All your scripts should be exactly two lines long ($ wc -l file should print 2)
  • All your files should end with a new line
  • The first line of all your files should be exactly #!/bin/bash

More Info

Betty linter

To run the Betty linter just with command betty <filename>:

  • Go to the Betty repository
  • Clone the repo to your local machine
  • cd into the Betty directory
  • Install the linter with sudo ./install.sh
  • emacs or vi a new file called betty, and copy the script below:
#!/bin/bash
# Simply a wrapper script to keep you from having to use betty-style
# and betty-doc separately on every item.
# Originally by Tim Britton (@wintermanc3r), multiargument added by
# Larry Madeo (@hillmonkey)

BIN_PATH="/usr/local/bin"
BETTY_STYLE="betty-style"
BETTY_DOC="betty-doc"

if [ "$#" = "0" ]; then
    echo "No arguments passed."
    exit 1
fi

for argument in "$@" ; do
    echo -e "\n========== $argument =========="
    ${BIN_PATH}/${BETTY_STYLE} "$argument"
    ${BIN_PATH}/${BETTY_DOC} "$argument"
done
  • Once saved, exit file and change permissions to apply to all users with chmod a+x betty
  • Move the betty file into /bin/ directory or somewhere else in your $PATH with sudo mv betty /bin/

You can now type betty <filename> to run the Betty linter!

Tasks

0. Preprocessor

mandatory

Write a script that runs a C file through the preprocessor and save the result into another file.

  • The C file name will be saved in the variable $CFILE
  • The output should be saved in the file c
julien@ubuntu:~/c/0x00$ cat main.c
#include <stdio.h>

/**
 * main - Entry point
 *
 * Return: Always 0 (Success)
 */
int main(void)
{
    return (0);
}
julien@ubuntu:~/c/0x00$ export CFILE=main.c
julien@ubuntu:~/c/0x00$ ./0-preprocessor
julien@ubuntu:~/c/0x00$ tail c
# 942 "/usr/include/stdio.h" 3 4

# 2 "main.c" 2

# 3 "main.c"
int main(void)
{
 return (0);
}
julien@ubuntu:~/c/0x00$

Repo:

  • GitHub repository: alx-low_level_programming
  • Directory: 0x00-hello_world
  • File: 0-preprocessor

1. Compiler

mandatory

Write a script that compiles a C file but does not link.

  • The C file name will be saved in the variable $CFILE
  • The output file should be named the same as the C file, but with the extension .o instead of .c.
    • Example: if the C file is main.c, the output file should be main.o
julien@ubuntu:~/c/0x00$ export CFILE=main.c
julien@ubuntu:~/c/0x00$ cat main.c
#include <stdio.h>

/**
 * main - Entry point
 *
 * Return: Always 0 (Success)
 */
int main(void)
{
    return (0);
}
julien@ubuntu:~/c/0x00$ ./1-compiler
julien@ubuntu:~/c/0x00$ ls
0-preprocessor  1-compiler   c            main.o
Makefile               100-intel      main.c  main.s
julien@ubuntu:~/c/0x00$ cat -v main.o | head
^?ELF^B^A^A^@^@^@^@^@^@^@^@^@^A^@>^@^A^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^P^B^@^@^@^@^@^@^@^@^@^@@^@^@^@^@^@@^@^K^@^H^@UHM-^IM-eM-8^@^@^@^@]M-C^@GCC: (Ubuntu 5.4.0-6ubuntu1~16.04.2) 5.4.0 20160609^@^T^@^@^@^@^@^@^@^AzR^@^Ax^P^A^[^L^G^HM-^P^A^@^@^\^@^@^@^\^@^@^@^@^@^@^@^K^@^@^@^@A^N^PM-^F^BC^M^FF^L^G^H^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^A^@^@^@^D^@M-qM-^?^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^C^@^A^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^C^@^B^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^C^@^C^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^C^@^E^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^C^@^F^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^C^@^D^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^H^@^@^@^R^@^A^@^@^@^@^@^@^@^@^@^K^@^@^@^@^@^@^@^@main.c^@main^@^@^@^@ ^@^@^@^@^@^@^@^B^@^@^@^B^@^@^@^@^@^@^@^@^@^@^@^@.symtab^@.strtab^@.shstrtab^@.text^@.data^@.bss^@.comment^@.note.GNU-stack^@.rela.eh_frame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
^@^@^@^H^@^@^@^H^@^@^@^@^@^@^@^X^@^@^@^@^@^@^@  ^@^@^@^C^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@M-^P^A^@^@^@^@^@^@^M^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^A^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@julien@ubuntu:~/c/0x00$

Repo:

  • GitHub repository: alx-low_level_programming
  • Directory: 0x00-hello_world
  • File: 1-compiler

2. Assembler

mandatory

Write a script that generates the assembly code of a C code and save it in an output file.

  • The C file name will be saved in the variable $CFILE
  • The output file should be named the same as the C file, but with the extension .s instead of .c.
    • Example: if the C file is main.c, the output file should be main.s
julien@ubuntu:~/c/0x00$ export CFILE=main.c
julien@ubuntu:~/c/0x00$ cat main.c
#include <stdio.h>

/**
 * main - Entry point
 *
 * Return: Always 0 (Success)
 */
int main(void)
{
    return (0);
}
julien@ubuntu:~/c/0x00$ ./2-assembler
julien@ubuntu:~/c/0x00$ ls
0-preprocessor  1-compiler  2-assembler c  main.c  main.s  Makefile
julien@ubuntu:~/c/0x00$ cat main.s
    .file   "main.c"
    .text
    .globl  main
    .type   main, @function
main:
.LFB0:
    .cfi_startproc
    pushq   %rbp
    .cfi_def_cfa_offset 16
    .cfi_offset 6, -16
    movq    %rsp, %rbp
    .cfi_def_cfa_register 6
    movl    $0, %eax
    popq    %rbp
    .cfi_def_cfa 7, 8
    ret
    .cfi_endproc
.LFE0:
    .size   main, .-main
    .ident  "GCC: (Ubuntu 5.4.0-6ubuntu1~16.04.2) 5.4.0 20160609"
    .section    .note.GNU-stack,"",@progbits
julien@ubuntu:~/c/0x00$

Repo:

  • GitHub repository: alx-low_level_programming
  • Directory: 0x00-hello_world
  • File: 2-assembler

3. Name

mandatory

Write a script that compiles a C file and creates an executable named cisfun.

  • The C file name will be saved in the variable $CFILE
julien@ubuntu:~/c/0x00$ export CFILE=main.c
julien@ubuntu:~/c/0x00$ cat main.c
#include <stdio.h>

/**
 * main - Entry point
 *
 * Return: Always 0 (Success)
 */
int main(void)
{
    return (0);
}
julien@ubuntu:~/c/0x00$ ./3-name
julien@ubuntu:~/c/0x00$ ls
0-preprocessor  1-compiler   3-name  cisfun  main.o  Makefile
100-intel       2-assembler  c       main.c  main.s
julien@ubuntu:~/c/0x00$

Repo:

  • GitHub repository: alx-low_level_programming
  • Directory: 0x00-hello_world
  • File: 3-name

4. Hello, puts

mandatory

Write a C program that prints exactly "Programming is like building a multilingual puzzle, followed by a new line.

  • Use the function puts
  • You are not allowed to use printf
  • Your program should end with the value 0
julien@ubuntu:~/c/0x00$ gcc -Wall -Werror -Wextra -pedantic -std=gnu89 4-puts.c && ./a.out
"Programming is like building a multilingual puzzle
julien@ubuntu:~/c/0x00$ echo $?
0
julien@ubuntu:~/c/0x00$

Repo:

  • GitHub repository: alx-low_level_programming
  • Directory: 0x00-hello_world
  • File: 4-puts.c

5. Hello, printf

mandatory

Write a C program that prints exactly with proper grammar, but the outcome is a piece of art,, followed by a new line.

  • Use the function printf
  • You are not allowed to use the function puts
  • Your program should return 0
  • Your program should compile without warning when using the -Wall gcc option
julien@ubuntu:~/c/0x00$ gcc -Wall -Werror -Wextra -pedantic -std=gnu89 5-printf.c
julien@ubuntu:~/c/0x00$ ./a.out
with proper grammar, but the outcome is a piece of art,
julien@ubuntu:~/c/0x00$ echo $?
0
julien@ubuntu:~/c/0x00$

Repo:

  • GitHub repository: alx-low_level_programming
  • Directory: 0x00-hello_world
  • File: 5-printf.c

6. Size is not grandeur, and territory does not make a nation

mandatory

Write a C program that prints the size of various types on the computer it is compiled and run on.

  • You should produce the exact same output as in the example
  • Warnings are allowed
  • Your program should return 0
  • You might have to install the package libc6-dev-i386 on your Linux (Vagrant) to test the -m32 gcc option
julien@ubuntu:~/c/0x00$ gcc 6-size.c -m32 -o size32 2> /tmp/32
julien@ubuntu:~/c/0x00$ gcc 6-size.c -m64 -o size64 2> /tmp/64
julien@ubuntu:~/c/0x00$ ./size32
Size of a char: 1 byte(s)
Size of an int: 4 byte(s)
Size of a long int: 4 byte(s)
Size of a long long int: 8 byte(s)
Size of a float: 4 byte(s)
julien@ubuntu:~/c/0x00$ ./size64
Size of a char: 1 byte(s)
Size of an int: 4 byte(s)
Size of a long int: 8 byte(s)
Size of a long long int: 8 byte(s)
Size of a float: 4 byte(s)
julien@ubuntu:~/c/0x00$ echo $?
0
julien@ubuntu:~/c/0x00$

Repo:

  • GitHub repository: alx-low_level_programming
  • Directory: 0x00-hello_world
  • File: 6-size.c

Done! Help Check your code Get a sandbox

7. Intel

#advanced

Write a script that generates the assembly code (Intel syntax) of a C code and save it in an output file.

  • The C file name will be saved in the variable $CFILE.
  • The output file should be named the same as the C file, but with the extension .s instead of .c.
    • Example: if the C file is main.c, the output file should be main.s
julien@ubuntu:~/c/0x00$ export CFILE=main.c
julien@ubuntu:~/c/0x00$ cat main.c
#include <stdio.h>

/**
 * main - Entry point
 *
 * Return: Always 0 (Success)
 */
int main(void)
{
    return (0);
}
julien@ubuntu:~/c/0x00$ ./100-intel
julien@ubuntu:~/c/0x00$ cat main.s
    .file   "main.c"
    .intel_syntax noprefix
    .text
    .globl  main
    .type   main, @function
main:
.LFB0:
    .cfi_startproc
    push    rbp
    .cfi_def_cfa_offset 16
    .cfi_offset 6, -16
    mov rbp, rsp
    .cfi_def_cfa_register 6
    mov eax, 0
    pop rbp
    .cfi_def_cfa 7, 8
    ret
    .cfi_endproc
.LFE0:
    .size   main, .-main
    .ident  "GCC: (Ubuntu 5.4.0-6ubuntu1~16.04.2) 5.4.0 20160609"
    .section    .note.GNU-stack,"",@progbits
julien@ubuntu:~/c/0x00$

Repo:

  • GitHub repository: alx-low_level_programming
  • Directory: 0x00-hello_world
  • File: 100-intel

Done! Help Check your code Get a sandbox

8. UNIX is basically a simple operating system, but you have to be a genius to understand the simplicity

#advanced

Write a C program that prints exactly and that piece of art is useful" - Dora Korpar, 2015-10-19, followed by a new line, to the standard error.

  • You are not allowed to use any functions listed in the NAME section of the man (3) printf or man (3) puts
  • Your program should return 1
  • Your program should compile without any warnings when using the -Wall gcc option
julien@ubuntu:~/c/0x00$ gcc -Wall -Werror -Wextra -pedantic -std=gnu89 -o quote 101-quote.c
julien@ubuntu:~/c/0x00$ ./quote
and that piece of art is useful" - Dora Korpar, 2015-10-19
julien@ubuntu:~/c/0x00$ echo $?
1
julien@ubuntu:~/c/0x00$ ./quote 2> q
julien@ubuntu:~/c/0x00$ cat q
and that piece of art is useful" - Dora Korpar, 2015-10-19
julien@ubuntu:~/c/0x00$ grep printf < 101-quote.c
julien@ubuntu:~/c/0x00$ grep put < 101-quote.c
julien@ubuntu:~/c/0x00$

Repo:

  • GitHub repository: alx-low_level_programming
  • Directory: 0x00-hello_world
  • File: 101-quote.c