0x07-pointers_arrays_strings

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

Resources

Read or watch:

• C - Pointer to Pointer
• C – Pointer to Pointer with example
• Multi-dimensional Arrays in C
• Two dimensional (2D) arrays in C programming with example

Learning Objectives

General

• What are pointers to pointers and how to use them
• What are multidimensional arrays and how to use them
• What are the most common C standard library functions to manipulate strings

Tasks

0. memset

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

Requirements:

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

Mode: mandatory

File: 0-memset.c

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1. memcpy

• Write a function that copies memory area.

Requirements:

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

Mode: mandatory

File: 1-memcpy.c

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2. strchr

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

Requirements:

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

Mode: mandatory

File: 2-strchr.c

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3. strspn

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

Requirements:

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

Mode: mandatory

File: 3-strspn.c

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4. strpbrk

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

Requirements:

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

Mode: mandatory

File: 4-strpbrk.c

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5. strstr

• Write a function that locates a substring.

Requirements:

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.

Mode: mandatory

File: 5-strstr.c

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6. Chess is mental torture

• Write a function that prints the chessboard.

Requirements:

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

Mode: mandatory

File: 7-print_chessboard.c

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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.

Requirements:

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

Mode: mandatory

File: 8-print_diagsums.c

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8. Double pointer, double fun

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

Requirements:

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

Mode: #advanced

File: 100-set_string.c

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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.

Requirements:

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

Mode: #advanced

File: 101-crackme_password