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]
587 questions
211
votes
3 answers
Return type of '?:' (ternary conditional operator)
Why does the first return a reference?
int x = 1;
int y = 2;
(x > y ? x : y) = 100;
While the second does not?
int x = 1;
long y = 2;
(x > y ? x : y) = 100;
Actually, the second did not compile at all - "not lvalue left of assignment".
Yola
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89
votes
9 answers
Why doesn't a+++++b work?
int main ()
{
int a = 5,b = 2;
printf("%d",a+++++b);
return 0;
}
This code gives the following error:
error: lvalue required as increment operand
But if I put spaces throughout a++ + and ++b, then it works fine.
int main ()
{
int a =…
Barshan Das
- 3,451
- 3
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- 44
74
votes
3 answers
C++: is return value a L-value?
Consider this code:
struct foo
{
int a;
};
foo q() { foo f; f.a =4; return f;}
int main()
{
foo i;
i.a = 5;
q() = i;
}
No compiler complains about it, even Clang. Why q() = ... line is correct?
John
- 2,177
- 18
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53
votes
4 answers
How to determine programmatically if an expression is rvalue or lvalue in C++?
What's the best way to determine if an expression is a rvalue or lvalue in C++? Probably, this is not useful in practice but since I am learning rvalues and lvalues I thought it would be nice to have a function is_lvalue which returns true if the…
Giuseppe Pes
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41
votes
3 answers
Why and when does the ternary operator return an lvalue?
For a long time I thought that the ternary operator always returns an rvalue. But to my surprise it doesn't. In the following code I don't see the difference between the return value of foo and the return value of the ternary operator.
#include…
Soulimane Mammar
- 1,099
- 8
- 17
39
votes
6 answers
Function that accepts both lvalue and rvalue arguments
Is there a way to write a function in C++ that accepts both lvalue and rvalue arguments, without making it a template?
For example, suppose I write a function print_stream that reads from an istream and prints the data that was read to the screen,…
HighCommander4
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35
votes
1 answer
Is std::move(*this) a good pattern?
In order to make this code with C++11 reference qualifiers work as expected I have to introduce a std::move(*this) that doesn't sound right.
#include
struct A{
void gun() const&{std::cout << "gun const&" << std::endl;}
void gun()…
alfC
- 10,293
- 4
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- 88
32
votes
1 answer
Expression must be a modifiable L-value
I have here char text[60];
Then I do in an if:
if(number == 2)
text = "awesome";
else
text = "you fail";
and it always said expression must be a modifiable L-value.
Mysterigs
- 333
- 1
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- 8
32
votes
4 answers
Rvalue Reference is Treated as an Lvalue?
I posted this answer: https://stackoverflow.com/a/28459180/2642059 Which contains the following code:
void foo(string&& bar){
string* temp = &bar;
cout << *temp << " @:" << temp << endl;
}
Is bar an rvalue or an lvalue?
I ask because I…
Jonathan Mee
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- 241
31
votes
1 answer
How to change the value of an NSMutableArray at a particular index
[array objectAtIndex:i] doesn't work as an L value, so it can't be used to set the object at index i.
node ninja
- 28,340
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31
votes
3 answers
what is return type of assignment operator?
I am just starting C++. I am a bit confused about the return type of assignment and dereference operator. I am following the book C++ Primer. At various occasions, the author says that the return type of assignment operator is reference to the type…
oczkoisse
- 1,273
- 2
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- 30
30
votes
3 answers
Why pre-increment operator gives rvalue in C?
In C++, pre-increment operator gives lvalue because incremented object itself is returned, not a copy.
But in C, it gives rvalue. Why?
Happy Mittal
- 3,477
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30
votes
3 answers
Are literal strings and function return values lvalues or rvalues?
Just wonder if a literal string is an lvalue or an rvalue. Are other literals (like int, float, char etc) lvalue or rvalue?
Is the return value of a function an lvalue or rvalue?
How do you tell the difference?
Tim
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29
votes
3 answers
Why is it not a compiler error to assign to the result of a substr call?
I just discovered the most baffling error and I don't understand why the compiler did not flag it for me. If I write the following:
string s = "abcdefghijkl";
cout << s << endl;
s.substr(2,3) = "foo";
s.substr(8,1) = '.';
s.substr(9,1) = 4;
cout…
blahedo
- 834
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27
votes
2 answers
C++0x const RValue reference as function parameter
I am trying to understand why someone would write a function that takes a const rvalue reference.
In the code example below what purpose is the const rvalue reference function (returning "3").
And why does overload resolution preference the const…
MW_dev
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