Syntax

& cast-expression
* cast-expression

Remarks 

The & and * operators work together to reference and dereference pointers that are passed to functions. 

Referencing operator ( & ) 

Use the reference operator to pass the address of a pointer to a function outside of main(). 

The cast-expression operand must be one of the following:

• a function designator
• an lvalue designating an object that is not a bit field and is not declared with a register storage class specifier

Some non-lvalue identifiers, such as function names and array names, are automatically converted into “pointer-to-X” types when they appear in certain contexts. The & operator can be used with such objects, but its use is redundant and therefore discouraged. 

Consider the following example:

   T t1 = 1, t2 = 2;
   T *ptr = &t1;      // Initialized pointer
   *ptr = t2;           // Same effect as t1 = t2

T *ptr = &t1 is treated as

   T *ptr;
   ptr = &t1;

So it is ptr, or *ptr, that gets assigned. Once ptr has been initialized with the address &t1, it can be safely dereferenced to give the lvalue *ptr. 

Indirection operator ( * ) 

Use the asterisk (*) in a variable expression to create pointers. And use the indirect operator in external functions to get a pointer's value that was passed by reference. 

If the operand is of type pointer to function, the result is a function designator. 

If the operand is a pointer to an object, the result is an lvalue designating that object. 

The result of indirection is undefined if either of the following occur:

• 1. The cast-expression is a null pointer.
• 2. The cast-expression is the address of an automatic variable and execution of its block has terminated.