Question

1. A function can return a value of type T in one of several different ways. Which of these is correct? If correct, give a short declaration of a function that returns its value by these mechanism. Comment on the const methods of function return value. Comment on when there is danger involved in returning a reference of any kind from a function. Finally, which one of these returns an l-value and which an r-value?
   1. By value
   2. By lazy evaluation.
   3. By reference
   4. By const value
   5. By const reference

Answer 1

A function can return value a value of type T in one of several different ways . Which one these is correct

All of them are correct.

Give a short declaration of a function that returns its value by these mechanism:

1. By value

T test(T t)

{

return t;

}

2. By const value

  

const T test(const T t)

{

...

return t;

}

3. By reference

T& test(T& t)

{

...

return *t;

}

4. By const reference

const T& test(const T& t)

{

...

return *t;

}

5. By lazy evaluation

T get()

{

if (calculated)

{

return result;

}

calculated = true;

return result = function();

}

Comment on const method of function return value

A function becomes const when the const keyword is used in the function’s declaration. The idea of const functions is not to allow them to modify the object on which they are called.

A const member function can be called by any type of object. Non-const functions can be called by non-const objects only.

Here is the syntax of const member function in C++ language,

datatype function_name const();
In the below code we have made i as constant, hence if we try to change its value, we will get compile time error. Though we can use it for substitution for other variables.

int main
{
const int i = 17;
const int j = i + 17;
i++;
}

Comment on where there is danger involved in returning a reference of any kind from a function.

Never return any kind of reference of a local / Temporary variable.

Which one of these returns and L value and which  is an R value.

by value -- R-value

lazy evalution-- It can return L-value or R-value (based on implementation)

reference-- L-value

const value-- R-value

const reference--- L-value