I need help learning what pointers are and what they do in a simple way because I am a Beginner. All the yt videos i watch, always confuses with something with pointers.
#What are pointers and how can I use them?
alpine raven
scarlet wedgeBOT
stoic lotus
What do you think a pointer is after those videos? What you dont understand
weary ibex
In C every* variable exists somewhere in memory (or RAM*)
Memory basically being able to hold large number of bytes, with each byes being represented by a number representing its "location" called an address
A pointer is basically... just a number. A number representing an address in memory that holds some other data.
Assuming a is an int pointer (i.e. an address)
*a
Uses that number and reads the interger at the address a
Also, assume n is just an int (not a pointer)
&n
Will take the address of where n is located in memory and make a pointer to that address
wise bloom
In the simplest terms, a pointer is a type of value that points to a location in memory. A pointer itself doesn't "do" anything per se - rather, developers do things with the memory at the location the pointer refers to. What the developer can do with that pointer varies.
wise bloom
To explain the basic usage of a pointer, take this program:
;compile -Wall -Wpedantic -Werror -fsanitize=address,undefined -std=c23
#include <stddef.h>
#include <stdio.h>
typedef struct {
int age;
} Character;
void character_set_age(Character self, int age) {
self.age = age;
}
int main() {
Character some_char = {};
character_set_age(some_char, 32);
printf("Character age: %d\n", some_char.age);
return 0;
}
valid dragonBOT
wise bloom
The result isn't what we expected. We want it to print Character age: 32 - but instead it's zero. Looking at our function signature:
void character_set_age(Character self, int age) {}
It might look like we're taking in an instance of character, and that's what we are doing in a sense. In C, passing an argument by value creates a copy of the argument. So character_set_age isn't operating on some_char. Instead it's operating on a brand new Character value that only exists for the duration of the function. If we want to actually modify the character we've got, we need a way to refer to the memory that holds the original value. This is where pointers come in. Our function should look like this:
void character_set_age(Character *self, int age) {
self->age = age;
}
Now instead of taking in a Character, we take in a pointer to a region of memory holding a Character. Do note that instead of self.age = ... we use self->age = .... The -> operator allows us to access fields on the pointer as if we were operating on the type. It's a shorthand for what we call dereferencing. The expanded form of this would be:
(*self).age = age;
In a function, prepending * to the start of a pointer variable dereferences it: it accesses the memory at the given pointer and treats it as the type supposedly held by the pointer.
Going back to the main function, we want to somehow give character_set_age() a pointer. We do this via the addressof operator &:
character_set_age(&some_char, 32);
For any given value, prepending & to it will give you the memory address you can use to refer to that region of memory.
Putting it all together:
;compile -Wall -Wpedantic -Werror -fsanitize=address,undefined -std=c23
#include <stddef.h>
#include <stdio.h>
typedef struct {
int age;
} Character;
void character_set_age(Character *self, int age) {
self->age = age;
}
int main() {
Character some_char = {};
character_set_age(&some_char, 32);
printf("Character age: %d\n", some_char.age);
return 0;
}
!solved