Podcast
Questions and Answers
What is the error in the code int* y = &330;?
What is the error in the code int* y = &330;?
- The pointer y is not initialized.
- The address of a constant cannot be taken.
- The constant 330 is not a valid memory location.
- The address-of operator (&) requires an lvalue. (correct)
What is the purpose of the '&' symbol in the line int& foo() { return globalvar;}?
What is the purpose of the '&' symbol in the line int& foo() { return globalvar;}?
- It is the address-of operator.
- It is used to declare a pointer.
- It is the dereference operator.
- It defines the type of what's returned (a reference). (correct)
Why does the code foo() = 10; compile successfully?
Why does the code foo() = 10; compile successfully?
- Because foo() returns a pointer.
- Because foo() returns an lvalue reference. (correct)
- Because foo() returns an integer.
- Because foo() returns a constant.
What is an lvalue in C++?
What is an lvalue in C++?
What is the result when trying to declare a reference to a numeric constant?
What is the result when trying to declare a reference to a numeric constant?
What is the purpose of a reference in C++?
What is the purpose of a reference in C++?
What happens when passing a temporary rvalue to a function that takes a reference as an argument?
What happens when passing a temporary rvalue to a function that takes a reference as an argument?
What is the difference between an lvalue and an rvalue?
What is the difference between an lvalue and an rvalue?
Why can't you take the address of a temporary value?
Why can't you take the address of a temporary value?
What is an rvalue in C++?
What is an rvalue in C++?
Why can't a reference be declared for a numeric constant?
Why can't a reference be declared for a numeric constant?
Why does the code int x = 1; int* y = &x; compile successfully?
Why does the code int x = 1; int* y = &x; compile successfully?
What would be the consequence of allowing a reference to a numeric constant?
What would be the consequence of allowing a reference to a numeric constant?
Why does the compiler prevent the declaration of a reference to a numeric constant?
Why does the compiler prevent the declaration of a reference to a numeric constant?
What is the primary requirement for the operand on the left side of the assignment operator?
What is the primary requirement for the operand on the left side of the assignment operator?
What does the Rvalue concept do in an assignment operation?
What does the Rvalue concept do in an assignment operation?
Why would the assignment '30 = Age' result in an error?
Why would the assignment '30 = Age' result in an error?
What is the most common place to encounter the terms 'lvalue' and 'rvalue'?
What is the most common place to encounter the terms 'lvalue' and 'rvalue'?
What happens to the value previously stored in a variable when a new assignment is made?
What happens to the value previously stored in a variable when a new assignment is made?
What is the purpose of the distinction between 'lvalue' and 'rvalue' in programming?
What is the purpose of the distinction between 'lvalue' and 'rvalue' in programming?
Study Notes
Lvalue and Rvalue
- Lvalue refers to the left side of the assignment operator, which must be modifiable, usually a variable.
- Rvalue refers to the right side of the assignment operator, which pulls or fetches the value of the expression or operand.
Example of Lvalue and Rvalue
Age = 39is an example of an assignment whereAgeis an Lvalue and39is an Rvalue.
Restrictions on Lvalue and Rvalue
- The statement
30 = Ageis invalid because30is an Rvalue and cannot be on the left side of the assignment operator.
Lvalue and Rvalue in Compiler Error Messages
- The terms Lvalue and Rvalue are often encountered in compiler error and warning messages.
Definition of Lvalue and Rvalue
- An Lvalue is a value that can be assigned to, such as a variable, while an Rvalue is a value that can be assigned.
Functions Returning Lvalues
- A function can return an Lvalue, allowing the function call to be assigned to.
int& foo()is an example of a function that returns an Lvalue.
Converting Lvalues to RValues
- Lvalues can be converted to Rvalues, but not vice versa.
- In the example
int x = 1;,xis an Lvalue, but the addition operator wants an Rvalue.
Lvalues and References
- A reference is an Lvalue that points to an existing memory location.
int& yref = 10;is an invalid statement because a reference cannot be assigned to a numeric constant.
Passing Rvalues to Functions
- Passing a temporary Rvalue to a function that takes a reference as an argument is invalid.
void fnc(int& x) { } int main() { fnc(10); }is an example of invalid Rvalue to Lvalue conversion.
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Description
This quiz covers the concepts of Lvalue and Rvalue in programming languages, including their introduction and applications in assignment operators.
