0x07-pointers_arrays_strings

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

For this project well be taking a deeper dive into the following concepts

• Pointers

• Arrays

• Strings

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.

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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.

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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.

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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.

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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.

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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.

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6. Chess is mental torture

Write a function that prints the chessboard.

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

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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.

• 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.

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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);

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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.

• 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

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