Function return values

If a function is defined as having a return type of void, it should not return a value. C++ only In C++, a function which is defined as having a return type of void, or is a constructor or destructor, must not return a value.

If a function is defined as having a return type other than void, it should return a value. Under compilation for strict C99 conformance, a function defined with a return type must include an expression containing the value to be returned.

C++ only A function defined with a return type must include an expression containing the value to be returned.

When a function returns a value, the value is returned via a return statement to the caller of the function, after being implicitly converted to the return type of the function in which it is defined. The following code fragment shows a function definition including the return statement:

int add(int i, int j)
{
  return i + j; // return statement
}

The function add() can be called as shown in the following code fragment:

int a = 10,
    b = 20;
int answer = add(a, b); // answer is 30

In this example, the return statement initializes a variable of the returned type. The variable answer is initialized with the int value 30. The type of the returned expression is checked against the returned type. All standard and user-defined conversions are performed as necessary.

Each time a function is called, new copies of its variables with automatic storage are created. Because the storage for these automatic variables may be reused after the function has terminated, a pointer or reference to an automatic variable should not be returned. C++ only If a class object is returned, a temporary object may be created if the class has copy constructors or a destructor.