0x0F-function_pointers

0x0F. C - Function pointers

• By Alexandre Gautier
• Ongoing project - started 09-29-2021, must end by 09-30-2021 (in about 18 hours) - you're done with 0% of tasks.
• Checker will be released at 09-29-2021 06:00 PM
• QA review fully automated.

Resources

Read or watch:

• Function Pointer in C
• Pointers to functions
• Function Pointers in C / C++
• why pointers to functions?
• Everything you need to know about pointers in C

Learning Objectives

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

General

• What are function pointers and how to use them
• What does a function pointer exactly hold
• Where does a function pointer point to in the virtual memory

Requirements

General

• 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
• The only C standard library functions allowed are malloc, free and exit. Any use of functions like printf, puts, calloc, realloc 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 function_pointers.h
• Don't forget to push your header file
• All your header files should be include guarded

Tasks 0. What's my name mandatory

Write a function that prints a name.

Prototype: void print_name(char *name, void (*f)(char *));

julien@ubuntu:~/0x0e. Function pointers$ cat 0-main.c #include <stdio.h> #include "function_pointers.h"

/**

• print_name_as_is - prints a name as is
• @name: name of the person
• Return: Nothing. */ void print_name_as_is(char *name) { printf("Hello, my name is %s\n", name); }

/**

• print_name_uppercase - print a name in uppercase

• @name: name of the person

• Return: Nothing. */ void print_name_uppercase(char *name) { unsigned int i;

  printf("Hello, my uppercase name is "); i = 0; while (name[i]) { if (name[i] >= 'a' && name[i] <= 'z') { putchar(name[i] + 'A' - 'a'); } else { putchar(name[i]); } i++; } }

/**

• main - check the code
• Return: Always 0. */ int main(void) { print_name("Bob", print_name_as_is); print_name("Bob Dylan", print_name_uppercase); printf("\n"); return (0); } julien@ubuntu:/0x0e. Function pointers$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 0-main.c 0-print_name.c -o a julien@ubuntu:/0x0e. Function pointers$ ./a Hello, my name is Bob Hello, my uppercase name is BOB DYLAN julien@ubuntu:~/0x0e. Function pointers$

Repo:

GitHub repository: alx-low_level_programming
Directory: 0x0F-function_pointers
File: 0-print_name.c

1. If you spend too much time thinking about a thing, you'll never get it done mandatory

Write a function that executes a function given as a parameter on each element of an array.

Prototype: void array_iterator(int *array, size_t size, void (*action)(int));
where size is the size of the array
and action is a pointer to the function you need to use

julien@ubuntu:~/0x0e. Function pointers$ cat 1-main.c #include <stdio.h> #include "function_pointers.h"

/**

• print_elem - prints an integer
• @elem: the integer to print
• Return: Nothing. */ void print_elem(int elem) { printf("%d\n", elem); }

/**

• print_elem_hex - prints an integer, in hexadecimal
• @elem: the integer to print
• Return: Nothing. */ void print_elem_hex(int elem) { printf("0x%x\n", elem); }

/**

• main - check the code

• Return: Always 0. */ int main(void) { int array[5] = {0, 98, 402, 1024, 4096};

  array_iterator(array, 5, &print_elem); array_iterator(array, 5, &print_elem_hex); return (0); } julien@ubuntu:/0x0e. Function pointers$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 1-main.c 1-array_iterator.c -o b julien@ubuntu:/0x0e. Function pointers$ ./b 0 98 402 1024 4096 0x0 0x62 0x192 0x400 0x1000 julien@ubuntu:~//0x0e. Function pointers$

Repo:

GitHub repository: alx-low_level_programming
Directory: 0x0F-function_pointers
File: 1-array_iterator.c

2. To hell with circumstances; I create opportunities mandatory

Write a function that searches for an integer.

Prototype: int int_index(int *array, int size, int (*cmp)(int));
where size is the number of elements in the array array
cmp is a pointer to the function to be used to compare values
int_index returns the index of the first element for which the cmp function does not return 0
If no element matches, return -1
If size <= 0, return -1

julien@ubuntu:~/0x0e. Function pointers$ cat 2-main.c #include <stdio.h> #include "function_pointers.h"

/**

• is_98 - check if a number is equal to 98
• @elem: the integer to check
• Return: 0 if false, something else otherwise. */ int is_98(int elem) { return (98 == elem); }

/**

• is_strictly_positive - check if a number is greater than 0
• @elem: the integer to check
• Return: 0 if false, something else otherwise. */ int is_strictly_positive(int elem) { return (elem > 0); }

/**

• abs_is_98 - check if the absolute value of a number is 98
• @elem: the integer to check
• Return: 0 if false, something else otherwise. */ int abs_is_98(int elem) { return (elem == 98 || -elem == 98); }

/**

• main - check the code

• Return: Always 0. */ int main(void) { int array[20] = {0, -98, 98, 402, 1024, 4096, -1024, -98, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 98}; int index;

  index = int_index(array, 20, is_98); printf("%d\n", index); index = int_index(array, 20, abs_is_98); printf("%d\n", index); index = int_index(array, 20, is_strictly_positive); printf("%d\n", index); return (0); } julien@ubuntu:/0x0e. Function pointers$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 2-main.c 2-int_index.c -o c julien@ubuntu:/0x0e. Function pointers$ ./c 2 1 2 julien@ubuntu:~/0x0e. Function pointers$

Repo:

GitHub repository: alx-low_level_programming
Directory: 0x0F-function_pointers
File: 2-int_index.c

3. A goal is not always meant to be reached, it often serves simply as something to aim at mandatory

Write a program that performs simple operations.

You are allowed to use the standard library
Usage: calc num1 operator num2
You can assume num1 and num2 are integers, so use the atoi function to convert them from the string input to int
operator is one of the following:
    +: addition
    -: subtraction
    *: multiplication
    /: division
    %: modulo
The program prints the result of the operation, followed by a new line
You can assume that the result of all operations can be stored in an int
if the number of arguments is wrong, print Error, followed by a new line, and exit with the status 98
if the operator is none of the above, print Error, followed by a new line, and exit with the status 99
if the user tries to divide (/ or %) by 0, print Error, followed by a new line, and exit with the status 100

This task requires that you create four different files.

3-calc.h

This file should contain all the function prototypes and data structures used by the program. You can use this structure:

/**

• struct op - Struct op
• @op: The operator
• @f: The function associated */ typedef struct op { char *op; int (*f)(int a, int b); } op_t;

3-op_functions.c

This file should contain the 5 following functions (not more):

op_add: returns the sum of a and b. Prototype: int op_add(int a, int b);
op_sub: returns the difference of a and b. Prototype: int op_sub(int a, int b);
op_mul: returns the product of a and b. Prototype: int op_mul(int a, int b);
op_div: returns the result of the division of a by b. Prototype: int op_div(int a, int b);
op_mod: returns the remainder of the division of a by b. Prototype: int op_mod(int a, int b);

3-get_op_func.c

This file should contain the function that selects the correct function to perform the operation asked by the user. You’re not allowed to declare any other function.

Prototype: int (*get_op_func(char *s))(int, int);
where s is the operator passed as argument to the program
This function returns a pointer to the function that corresponds to the operator given as a parameter. Example: get_op_func("+") should return a pointer to the function op_add
You are not allowed to use switch statements
You are not allowed to use for or do ... while loops
You are not allowed to use goto
You are not allowed to use else
You are not allowed to use more than one if statement in your code
You are not allowed to use more than one while loop in your code
If s does not match any of the 5 expected operators (+, -, *, /, %), return NULL
You are only allowed to declare these two variables in this function:

op_t ops[] = {
    {"+", op_add},
    {"-", op_sub},
    {"*", op_mul},
    {"/", op_div},
    {"%", op_mod},
    {NULL, NULL}
};
int i;

3-main.c

This file should contain your main function only.

You are not allowed to code any other function than main in this file
You are not allowed to directly call op_add, op_sub, op_mul, op_div or op_mod from the main function
You have to use atoi to convert arguments to int
You are not allowed to use any kind of loop
You are allowed to use a maximum of 3 if statements

Compilation and examples

julien@ubuntu:/0x0e. Function pointers$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 3-main.c 3-op_functions.c 3-get_op_func.c -o calc julien@ubuntu:/0x0e. Function pointers$ ./calc 1 + 1 2 julien@ubuntu:/0x0e. Function pointers$ ./calc 97 + 1 98 julien@ubuntu:/0x0e. Function pointers$ ./calc 1024 / 10 102 julien@ubuntu:/0x0e. Function pointers$ ./calc 1024 '*' 98 100352 julien@ubuntu:/0x0e. Function pointers$ ./calc 1024 '*' 98 Error julien@ubuntu:/0x0e. Function pointers$ ./calc 1024 - 98 926 julien@ubuntu:/0x0e. Function pointers$ ./calc 1024 '%' 98 44 julien@ubuntu:~/0x0e. Function pointers$

Repo:

GitHub repository: alx-low_level_programming
Directory: 0x0F-function_pointers
File: 3-main.c, 3-op_functions.c, 3-get_op_func.c, 3-calc.h