L-value represents the address of the value. "L" stands for the left side, because the address it is what is required when the variable appears on the left side of an assignment operation.
Questions tagged [lvalue]
661 questions
4
votes
5 answers
What's the deal with temporary objects and references?
One can frequently read that you cannot bind normal lvalue reference to temporary object. Because of that one can frequently see methods of class A taking const A& as a parameter when they don't want to involve copying. However such construct is…
Argbart
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4
votes
2 answers
How to pass lvalue to function taking rvalue only without templates
My question is simple
#include
using namespace std;
template
void f(T&& i) {
cout << i << endl;
}
void g(int&& i) {
cout << i << endl;
}
int main() {
int i = 0;
f(i); // works fine
…
Ankit Rohilla
- 95
- 5
4
votes
2 answers
Why my object still gets copied when I tried to return a reference
class Obj {
public:
Obj(int aa, int bb): a(aa), b(bb) {}
Obj(const Obj& o) {a = o.a; b = o.b;std::cout << "copying" << std::endl;}
Obj(Obj&& o) {a = o.a; b = o.b;std::cout << "moving" << std::endl;}
int a;
int b;
};
const Obj&…
coin cheung
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- 25
4
votes
2 answers
"Expression resolves to an unused l-value" vs "Expression is unused"
Consider the following code:
class Foo {
let bar = "Hello world!"
init () {
self // Warning: Expression of type 'Foo' is unused
self.bar // Error: Expression resolves to an unused l-value
}
func test () {
…
John Montgomery
- 6,739
- 9
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- 68
4
votes
5 answers
Why rvalue reference as return type can't be initialization of non-const reference?
I read this question and I know that an rvalue referenec is an lvalue.
However, for this code, example 1,
int &&fun() {
return 1;
}
int main() {
int &a = fun();
}
When I compile it:
error: invalid initialization of non-const reference of…
namasikanam
- 256
- 3
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4
votes
3 answers
C++ lvalues and rvalues in template functions
I took sample from http://www.cplusplus.com/reference/utility/forward:
// forward example
#include // std::forward
#include // std::cout
// function with lvalue and rvalue reference overloads:
void overloaded (const…
J. S.
- 425
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4
votes
2 answers
CPP Reference in Constructor and Function
Am bit confused on the below code. `
class sample
{
public:
sample() { }
sample( sample& Obj ) { }
};
void fun( sample& Obj ) { }
int main()
{
sample s(sample());
fun( sample() );
return 0;
}
am getting the below…
Prasath Shanmugakani
- 129
- 5
4
votes
2 answers
Universal reference template type always evaluate to lvalue
My code:
#include
#include
#include
void store(std::string & val)
{
std::cout << "lvalue " << val << '\n';
}
void store(std::string && val)
{
std::cout << "rvalue " << val << '\n';
}
template void…
demalegabi
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4
votes
5 answers
Why ++(*p) is not giving l-value required error?
#include
int main()
{
int arr[] = {1, 2, 3, 4, 5};
int *p = arr;
++*p;
p += 2;
printf("%d", *p);
return 0;
}
Why is this code not giving any compile time error,My doubt is ++*p is evaluated as ++(*p) and *p will be…
Geeta
- 91
- 1
4
votes
1 answer
c++ is const pointer to literal valid?
I know lvalues can be converted into const reference. I'm curious if I can get a pointer to those lvalues.
If I write
const int* p = &3; //ERROR: lvalue required as unary operand '&'
I get this error. However,
const int* p = &((const int&)3);
this…
eivour
- 1,678
- 12
- 20
4
votes
2 answers
C++ - lvalue required as left operand of assignment
Consider the following code:
#include
using namespace std;
class X
{
int i;
public:
X(int ii = 0);
};
X::X(int ii) { i = ii; }
int a;
X f1() { return X(); }
int f2() { return a; }
int main() {
f1() = X(1);
f2() =…
George Cernat
- 1,323
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4
votes
5 answers
Is always the address of a reference equal to the address of origin?
This looks a very basic topic but very important to me.
The following example shows that the address of a reference variable is equal to the address of the original variable. I know this is what we can expect from the concept of C/C++. However, is…
ar2015
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4
votes
2 answers
Why does std::forward converts lvalue and rvalue to rvalue reference?
I suppose I am confused with std::forward.
My function which uses std::forward is following, but it is much simplified and modified to make explanation easily.
// This is an example code to explain my question simply.
template
mora
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4
votes
0 answers
How to programmatically check if an expression is r-value or l-value in C (possibly non-standard)
Suppose I would like to write a preprocessor macro which would have a conditional branch inside built on whether an argument to that macro is l-value or r-value. Is that achievable with C (not C++, not C11), possibly with GCC extensions?
Wojciech Migda
- 738
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4
votes
1 answer
"error: lvalue required as left operand of assignment" in conditional operator
I'm new to C and today I learnt "?" operator which is the short type of if-else statement. However, when I execute this code:
int b;
int x;
b=3<2?x=12:x=34;
I get an error "error: lvalue required as left operand of assignment". I don't understand…
F. Eser
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