0x0B-malloc_free

0x0B. C - malloc, free

The malloc function is used to allocate a certain amount of memory during the execution of a program. It will request a block of memory from the heap. If the request is granted, the operating system will reserve the requested amount of memory and malloc will return a pointer to the reserved space.

When the amount of memory is not needed anymore, you must return it to the operating system by calling the function free.

Automatic allocation

When you declare variables or when you use strings within double quotes, the program is taking care of all the memory allocation. You do not have to think about it.

/**
 * cisfun - function used for concept introduction
 * @n1: number of projects
 * @n2: number of tasks
 *
 * Return: nothing.
 */
void cisfun(unsigned int n1, unsigned int n2)
{
    int n;
    char c;
    int *ptr;
    char array[3];
}

Dynamic allocation

Malloc

The malloc function allocates a specific number of bytes in memory and returns a pointer to the allocated memory. This memory will have read and write permissions.

• Prototype: void *malloc(size_t size);
• where void * means it is a pointer to the type of your choice
• and size is the number of bytes your need to allocate

#include <stdio.h>
#include <stdlib.h>

/**
 * main - introduction to malloc and ree
 *
 * Return: 0.
 */
int main(void)
{
    char *str;

    str = malloc(sizeof(char) * 3);
    str[0] = 'O';
    str[1] = 'K';
    str[2] = '\0';
    printf("%s\n", str);
    return (0);
}

// OUTPUT
OK

Tasks

0. Float like a butterfly, sting like a bee

Write a function that creates an array of chars, and initializes it with a specific char.

• Prototype: char *create_array(unsigned int size, char c);
• Returns NULL if size = 0
• Returns a pointer to the array, or NULL if it fails

solution

1. The woman who has no imagination has no wings

Write a function that returns a pointer to a newly allocated space in memory, which contains a copy of the string given as a parameter.

• Prototype: char *_strdup(char *str);
• The _strdup() function returns a pointer to a new string which is a duplicate of the string str. Memory for the new string is obtained with malloc, and can be freed with free.
• Returns NULL if str = NULL
• On success, the _strdup function returns a pointer to the duplicated string. It returns NULL if insufficient memory was available

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

solution

2. He who is not courageous enough to take risks will accomplish nothing in life

Write a function that concatenates two strings.

• Prototype: char *str_concat(char *s1, char *s2);
• The returned pointer should point to a newly allocated space in memory which contains the contents of s1, followed by the contents of s2, and null terminated
• if NULL is passed, treat it as an empty string
• The function should return NULL on failure

solution

3. If you even dream of beating me you'd better wake up and apologize

Write a function that returns a pointer to a 2 dimensional array of integers.

• Prototype: int **alloc_grid(int width, int height);
• Each element of the grid should be initialized to 0
• The function should return NULL on failure
• If width or height is 0 or negative, return NULL

solution

4. It's not bragging if you can back it up

Write a function that frees a 2 dimensional grid previously created by your alloc_grid function.

• Prototype: void free_grid(int **grid, int height);
• Note that we will compile with your alloc_grid.c file. Make sure it compiles.

solution

5. It isn't the mountains ahead to climb that wear you out; it's the pebble in your shoe

Write a function that concatenates all the arguments of your program.

• Prototype: char *argstostr(int ac, char **av);
• Returns NULL if ac == 0 or av == NULL
• Returns a pointer to a new string, or NULL if it fails
• Each argument should be followed by a \n in the new string

solution

6. I will show you how great I am

Write a function that splits a string into words.

• Prototype: char **strtow(char *str);
• The function returns a pointer to an array of strings (words)
• Each element of this array should contain a single word, null-terminated
• The last element of the returned array should be NULL
• Words are separated by spaces
• Returns NULL if str == NULL or str == ""
• If your function fails, it should return NULL

solution