C++ lvalue_rvalue

Table of contents

int GetValue() {
  int value = 10;
  fmt::print("GetValue() {}\n", value);
  return value;
}

int& GetValue2() {
  static int value = 10;
  fmt::print("GetValue2() {}\n", value);
  return value;
}

void SetValue(int value) { fmt::print("SetValue({})\n", value); }


This function only accept lvalues.
//-- This function only accept lvalues.

void SetValue2(int& value) { fmt::print("SetValue2({})\n", value); }


The `const` changes the behavior here to accept rvalues too.
//-- The `const` changes the behavior here to accept rvalues too.

void SetValue3(const int& value) { fmt::print("SetValue3({})\n", value); }

void PrintName(string& lvalue) {
  fmt::print("Full name is: {} lvalue\n", lvalue);
}

void PrintName2(string&& rvalue) {
  fmt::print("Full name is: {} rvalue\n", rvalue);
}

  int a = GetValue();
  fmt::print("value returned by GetValue() is {}\n", a);

  // GetValue() = 10; // this operation is not possible
  GetValue2() = 20;  // lvalue is ok
  fmt::print("Value stored into function GetValue2() is {}\n", GetValue2());

  int b = 10;    // b is a lvalue  10 is a rvalue
  SetValue(b);   // call with lvalue
  SetValue(10);  // call with rvalue (temporary object)

  SetValue2(b);  // call with lvalue
  // SetValue2(10);  // this operation is not possible
  SetValue3(10);  // ok, the compiler will create a temporary variable and get a
                  // reference for it.
                  // int temp = 10; SetValue(temp);

  string firstName = "Geraldo";
  string lastName = "Ribeiro";
  string fullName = firstName + lastName;

  PrintName(fullName);  // ok lvalue
  // PrintName(firstName + lastName); // not ok, rvalue
  //  again in change the function signature to accept const string& will works
  PrintName2(firstName + lastName);  // ok rvalue
  // PrintName2(fullName); // not ok, lvalue

## Possible output


```txt
GetValue() 10
value returned by GetValue() is 10
GetValue2() 10
GetValue2() 20
Value stored into function GetValue2() is 20
SetValue(10)
SetValue(10)
SetValue2(10)
SetValue3(10)
Full name is: GeraldoRibeiro lvalue
Full name is: GeraldoRibeiro rvalue

References

• ▶️lvalues and rvalues in C++
• title