Questions tagged [const-reference]
131 questions
12
votes
1 answer
Passing rvalue reference to const lvalue reference paremeter
I am trying to understand C++11 rvalue references and how to use them for optimal performance in my code.
Let's say we have a class A that has a member pointer to a large amount of dynamically allocated data.
Furthermore, a method foo(const A& a)…
Sven
- 143
- 1
- 1
- 7
11
votes
2 answers
Implicit conversion : const reference vs non-const reference vs non-reference
Consider this code,
struct A {};
struct B { B(const A&) {} };
void f(B)
{
cout << "f()"<
Nawaz
- 353,942
- 115
- 666
- 851
11
votes
3 answers
Why can a const reference to a string parameter take string literals?
Why can a const reference to a string parameter take string literals? String literals, like "hello", are not variables, so why is this code valid?
class CVector {
public:
int x, y;
CVector() {};
~CVector() { delete ptr;…
user7982333
11
votes
4 answers
Binding const& of temporary: No compiler warning?
I have a TestClass with a const& member variable. I know from various places and own experiences that it is a bad idea to initialize this const& with the reference to a temporary value. So I was quite suprised that the following code will compile…
user3520187
- 168
- 7
10
votes
5 answers
Reference initialization in C++
Can anybody explain to me why there is a difference between these two statements?
class A{};
const A& a = A(); // correct
A& b = A(); // wrong
It says
invalid initialization of non-const reference of type A& from a…
skydoor
- 25,218
- 52
- 147
- 201
9
votes
2 answers
Variadic template specialization with const reference
How to specialize variadic template function that has const reference for an argument?
Example:
template
T foo(Args... args) = delete;
template<> int foo(int a, const char* str, const Test& t) { .... } // Fails to…
Bected
- 153
- 7
9
votes
7 answers
How to return a const QString reference in case of failure?
consider the following code:
const QString& MyClass::getID(int index) const
{
if (i < myArraySize && myArray[i]) {
return myArray[i]->id; // id is a QString
} else {
return my_global_empty_qstring; // is a global empty…
moala
- 5,094
- 9
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- 66
9
votes
2 answers
What exactly happens when returning const reference to a local object?
struct A {
A(int) : i(new int(783)) {
std::cout << "a ctor" << std::endl;
}
A(const A& other) : i(new int(*(other.i))) {
std::cout << "a copy ctor" << std::endl;
}
~A() {
std::cout << "a dtor" <<…
Alexander
- 779
- 8
- 17
8
votes
2 answers
Prevent temporary from extending its lifetime?
This may be impossible, but I was wondering if it was possible to keep a temporary from ever lasting past its original expression. I have a chain of objects which point to parent objects, and a member function which will create a child object, a…
zounds
- 773
- 8
- 17
8
votes
3 answers
Why does this call by reference create a new instance?
Im calling a method foo by const ref:
// method, which is being called
void foo(const Entity & ent);
// call
Entity* e = new Entity;
foo(e); // wrong: missing * but compiles
This piece of code does not only compile, it creates a new instance of…
atamanroman
- 11,607
- 7
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- 81
8
votes
4 answers
Warning C4172: Returning a reference to const std::string bound to a local variable. How safe is it?
I was just building one of our projects at work and I see a new function was added:
const std::string& ClassName::MethodName() const
{
return "";
}
The compiler gives a warning:
Warning C4172: returning address of local variable or temporary
I…
Armen Tsirunyan
- 130,161
- 59
- 324
- 434
7
votes
1 answer
Best practice for getters with ref-qualifier
The following code causes undefined behaviour:
class T
{
public:
const std::string& get() const { return s_; }
private:
std::string s_ { "test" };
}
void breaking()
{
const auto& str = T{}.get();
// do sth with "str" <--…
Tim
- 143
- 1
- 5
7
votes
1 answer
Visual Studio is not creating temporary object when typecasting?
I'm using Visual Studio Express 2013 and is fooling around a bit trying to learn about different things in C++.
I stumbled upon an interesting bug in the compiler where it doesn't seem to create a temporary object when explicitly type casting to the…
dnfs
- 73
- 5
6
votes
1 answer
Is the lifetime of a C++ temporary object created in ?: expression extended by binding it to a local const reference?
It is not clear to me whether the lifetime of a temporary object would be extended by binding it to a const reference in a ?: expression:
class Foo {...};
Foo *someLValue = ...;
const Foo& = someLValue ? *someLValue : Foo();
Is the lifetime of…
Palo
- 1,051
- 8
- 12
6
votes
2 answers
const reference to a temporary object becomes broken after function scope (life time)
While asking this question, I learned const reference to a temporary object is valid in C++:
int main ()
{
int a = 21;
int b = 21;
//error: invalid initialization of non-const reference
//int & sum = a + b;e [...]
//OK
int const &…
oHo
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