Cpp pointers & references

Pointers refer to the memory address a value is stored in. Passing a pointer as an argument, rather than the actual variable is generally a MUCH cheaper operation than copying the entire value into a new memory block.

Pointers

Using Pointers

int number_22  = 22;  // the number 22 is assigned the memory cell #1076
cout << &number_22;   // prints the POINTER, the memory-address of the variable
cout << *1076;        // prints 22. '*' indicates the value is a memory-address

struct User{
    string name;
    int age;
};		
User will;                         // create empty user `will`
int * ptr_will = &will             // create pointer to `will`s memory addr

ptr_will->name = "Will Pittman";  // set attr using a pointer
*will.age = 200;                  // set attr using a pointer (also valid)

Creating Pointers

int    * myvariable;			// creates a pointer of type 'int'
string * myvariable;			// creates a pointer of type 'string'

Nesting Pointers

It is possible to make pointers point to other pointers. When initializing a variable to store the pointer, you require one * per level away from the actual pointer.

int *   mystr;		// a pointer, mystr
int **  mystr;		// a pointer, referencing a pointer
int *** mystr;		//	a pointer, referencing a pointer, referencing a pointer

Arithmetic

See pointer arithmetics on http://www.cplusplus.com/doc/tutorial/pointers/, it is explaned very well.

Pointers can be added to or subtracted from. Pointer addition adds in units in the size of the pointer. Say we had a float which occupied 3bits. Adding 1 to it would add 3. Adding 1 a second time would add 6, etc.

References

Pointers and references are very similar. The difference is

• a pointer must be dereferenced in order to be used. (it points to the memory addr)
• a reference is a copy of the variable. It does not need to be dereferenced to be used (it points to the value, without using extra space)

General Use

int i = 3;
int * pointer  = &i;   // &i refers to the address, (the pointer is made to refer to i's address)
int &reference = i;    // 'reference' can now be used interchangeably with i (without using more memory)

As Arguments

In order to mark an argument as a reference, you use a suffix of & after the type.

void my_func ( int& var_name ){
	cout << var_name;;
}