0x07-pointers_arrays_strings

Project

0x07. C - Even more pointers, arrays and strings

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Table of Contents

• Author Details
• Project Description
• Tasks
  • 0. memset
  • 1. memcpy
  • 2. strchr
  • 3. strspn
  • 4. strpbrk
  • 5. strstr
  • 6. Chess is mental torture
  • 7. The line of life is a ragged diagonal between duty and desire
  • 8. Double pointer, double fun
  • 9. My primary goal of hacking was the intellectual curiosity, the seduction of adventure

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Author Details

• Dean Robin Otsyeno - [email protected]

Project Description

• 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

Tasks

0

Table of Contents

0. memset

• Write a function that fills memory with a constant byte.

  • Prototype: char *_memset(char *s, char b, unsigned int n);
  • The _memset() function fills the first n bytes of the memory area pointed to by s with the constant byte b
  • Returns a pointer to the memory area s

• FYI: The standard library provides a similar function: memset. Run man memset to learn more

julien@ubuntu:~/0x07$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 0-main.c 0-memset.c -o 0-memset
julien@ubuntu:~/0x07$ ./0-memset
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
-------------------------------------------------
0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01
0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01
0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01
0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01
0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01
0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01
0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01
0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01
0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01
0x01 0x01 0x01 0x01 0x01 0x00 0x00 0x00

• Repo
  • GitHub repository: alx-low_level_programming
  • Directory: 0x07-pointers_arrays_strings
  • File: 0-memset.c
  • Example file: 0-main.c

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1

Table of Contents

1. memcpy

• Write a function that copies memory area.

  • Prototype: char *_memcpy(char *dest, char *src, unsigned int n);
  • The _memcpy() function copies n bytes from memory area src to memory area dest
  • Returns a pointer to dest

• FYI: The standard library provides a similar function: memcpy. Run man memcpy to learn more.

julien@ubuntu:~/0x07$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 1-main.c 1-memcpy.c -o 1-memcpy
julien@ubuntu:~/0x07$ ./1-memcpy
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
-------------------------------------------------
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x01 0x02 0x03 0x04 0x05 0x07 0x07 0x08 0x09 0x0a
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00

• Repo
  • GitHub repository: alx-low_level_programming
  • Directory: 0x07-pointers_arrays_strings
  • File: 1-memcpy.c
  • Example file: 1-main.c

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2

Table of Contents

2. strchr

• Write a function that locates a character in a string.

  • Prototype: char *_strchr(char *s, char c);
  • Returns a pointer to the first occurrence of the character c in the string s, or NULL if the character is not found

• FYI: The standard library provides a similar function: strchr. Run man strchr to learn more.

julien@ubuntu:~/0x07$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 2-main.c 2-strchr.c -o 2-strchr
julien@ubuntu:~/0x07$ ./2-strchr
llo

• Repo
  • GitHub repository: alx-low_level_programming
  • Directory: 0x07-pointers_arrays_strings
  • File: 2-strchr.c
  • Example file: 2-main.c

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3

Table of Contents

3. strspn

• Write a function that gets the length of a prefix substring.

  • Prototype: unsigned int _strspn(char *s, char *accept);
  • Returns the number of bytes in the initial segment of s which consist only of bytes from accept

• FYI: The standard library provides a similar function: strspn. Run man strspn to learn more.

julien@ubuntu:~/0x07$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 3-main.c 3-strspn.c -o 3-strspn
julien@ubuntu:~/0x07$ ./3-strspn
5

• Repo
  • GitHub repository: alx-low_level_programming
  • Directory: 0x07-pointers_arrays_strings
  • File: 3-strspn.c
  • Example file: 3-main.c

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4

Table of Contents

4. strpbrk

• Write a function that searches a string for any of a set of bytes.

  • Prototype: char *_strpbrk(char *s, char *accept);
  • The _strpbrk() function locates the first occurrence in the string s of any of the bytes in the string accept
  • Returns a pointer to the byte in s that matches one of the bytes in accept, or NULL if no such byte is found

  FYI: The standard library provides a similar function: strpbrk. Run man strpbrk to learn more.

julien@ubuntu:~/0x07$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 4-main.c 4-strpbrk.c -o 4-strpbrk
julien@ubuntu:~/0x07$ ./4-strpbrk
llo, world

• Repo
  • GitHub repository: alx-low_level_programming
  • Directory: 0x07-pointers_arrays_strings
  • File: 4-strpbrk.c
  • Example file: 4-main.c

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5

Table of Contents

5. strstr

• Write a function that locates a substring.

  • Prototype: char *_strstr(char *haystack, char *needle);
  • The _strstr() function finds the first occurrence of the substring needle in the string haystack. The terminating null bytes (\0) are not compared
  • Returns a pointer to the beginning of the located substring, or NULL if the substring is not found.

• FYI: The standard library provides a similar function: strstr. Run man strstr to learn more.

julien@ubuntu:~/0x07$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 5-main.c 5-strstr.c -o 5-strstr
julien@ubuntu:~/0x07$ ./5-strstr
world

• Repo
  • GitHub repository: alx-low_level_programming
  • Directory: 0x07-pointers_arrays_strings
  • File: 5-strstr.c
  • Example file: 5-main.c

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6

Table of Contents

6. Chess is mental torture

• Write a function that prints the chessboard.

  • Prototype: void print_chessboard(char (*a)[8]);

julien@ubuntu:~/0x07$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 _putchar.c 7-main.c 7-print_chessboard.c -o 7-print_chessboard
julien@ubuntu:~/0x07$ ./7-print_chessboard
rkbqkbkr
pppppppp




PPPPPPPP
RKBQKBKR

• Repo
  • GitHub repository: alx-low_level_programming
  • Directory: 0x07-pointers_arrays_strings
  • File: ``
  • Example file: 7-main.c

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7

Table of Contents

7. The line of life is a ragged diagonal between duty and desire

• Write a function that prints the sum of the two diagonals of a square matrix of integers.

  • Prototype: void print_diagsums(int *a, int size);
  • Format: see example
  • You are allowed to use the standard library

• Note that in the following example we are casting an int[][] into an int*. This is not something you should do. The goal here is to make sure you understand how an array of array is stored in memory.

julien@ubuntu:~/0x07$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 8-main.c 8-print_diagsums.c -o 8-print_diagsums
julien@ubuntu:~/0x07$ ./8-print_diagsums
113, 1016
1214556093, 1137318

• Repo
  • GitHub repository: alx-low_level_programming
  • Directory: 0x07-pointers_arrays_strings
  • File: 8-print_diagsums.c
  • Example file: 8-main.c

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8

Table of Contents

8. Double pointer, double fun

• Write a function that sets the value of a pointer to a char.

  • Prototype: void set_string(char **s, char *to);

julien@ubuntu:~/0x07$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 100-main.c 100-set_string.c -o 100-set_string
julien@ubuntu:~/0x07$ ./100-set_string 
Bob Dylan, Robert Allen
Bob Dylan, Bob Dylan

• Repo
  • GitHub repository: alx-low_level_programming
  • Directory: 0x07-pointers_arrays_strings
  • File: 100-set_string.c
  • Example file: 100-main.c

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9

Table of Contents

9. My primary goal of hacking was the intellectual curiosity, the seduction of adventure

• Create a file that contains the password for the crackme2 executable.

  • Your file should contain the exact password, no new line, no extra space
  • ltrace, ldd, gdb and objdump can help
  • You may need to install the openssl library to run the crakme2 program: sudo apt install libssl-dev
  • Edit the source list sudo nano /etc/apt/sources.list to add the following line: deb http://security.ubuntu.com/ubuntu xenial-security main Then sudo apt update and sudo apt install libssl1.0.0

• Repo
  • GitHub repository: alx-low_level_programming
  • Directory: 0x07-pointers_arrays_strings
  • File: 101-crackme_password

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_{Dean Robin Otsyeno - [email protected]}