30 April 2014

C++ Pointers & References Cheat Sheet

Tyler Young
Tyler Young @TylerAYoung @tylerayoung@fosstodon.org
Programming Cpp

My dirty little secret: I’ve spent too much time in fancy-pants languages like Java… and Python… and Ruby… and PHP… and Javascript… to remember what the & does all the time.

This is my cheat sheet. Hope it helps you too.

The Golden Rule

If & is used to declare a variable, it makes that variable a reference.

Otherwise, & is used to take the address of a variable.

Pointers

Initialization

int myInteger = 42;
int myIntPointer = &myInteger; // "address of"
cout << *myIntPointer; // prints 42

As a parameter

void foo( std::string * stringPtr ) {
    cout << *stringPtr; // prints "Aloha"
}
std::string s = "Aloha";
foo( &s ); // pass Aloha's address to the pointer

References

Pass-by-value

void foo( int x ) {
    x = 42; // x is passed by value, so no change occurs outside this function
}
int x = 0;
foo(x);
// x == 0

Pass-by-reference

void fooMutate( int &x ) {
    x = 42; // passed by reference, so x changes outside this scope
}

int x = 0;
fooMutate(x);
// x == 42

Declaring a reference (alias)

int x = 0;
int y = &x; // y is now an alias of x
y = 42;
// x == 42