- 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:
- 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
- You are tasked to come up with solutions for the tasks below yourself to meet with the above learning objectives.
- You will not be able to meet the objectives of this or any following project by copying and pasting someone else’s work.
- You are not allowed to publish any content of this project.
- Any form of plagiarism is strictly forbidden and will result in removal from the program.
- 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
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$
- GitHub repository: alx-low_level_programming
- Directory: 0x0F-function_pointers
- File: 0-print_name.c
- 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$
- GitHub repository: alx-low_level_programming
- Directory: 0x0F-function_pointers
- File: 1-array_iterator.c
- 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$
- 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)
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$
- 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