C Pointers
A pointer is a variable that stores the memory address of another variable, rather than a value directly. Pointers are declared using the * symbol, and are one of C's most distinctive and powerful features.
To get the value stored at the address a pointer holds, you 'dereference' it, also using the * symbol. Pointers enable efficient memory use, dynamic data structures, and passing data by reference.
type *pointerName = &variable;Declaring and using pointers
A pointer declaration looks like `int *p;`, meaning p can hold the address of an int. Assign it an address with `p = &age;`, then access the value it points to with `*p`.
Why pointers matter
Pointers let functions modify variables outside their own scope, enable dynamic memory allocation, and make working with arrays and strings efficient.
#include <stdio.h>
int main() {
int age = 25;
int *p = &age;
printf("%d\n", *p);
return 0;
}25p stores the address of age, and *p dereferences it to get the value 25.
#include <stdio.h>
int main() {
int age = 25;
int *p = &age;
*p = 30;
printf("%d\n", age);
return 0;
}30Writing through the dereferenced pointer *p changes the original variable age.
Key points
- A pointer stores the memory address of another variable.
- The * symbol both declares a pointer and dereferences it.
- Dereferencing lets you read or modify the pointed-to value.
- An uninitialized pointer is dangerous and should be set to NULL if unused.