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Questions tagged [const-cast]

Anything related to the `const_cast` operation in C++, i.e. a form of compile-time conversion where the `const` or `volatile` qualifiers are cast away (removed) from a variable.

Anything related to the const_cast operation in C++, i.e. a form of compile-time conversion where the const or volatile qualifiers are cast away (removed) from a variable.

See CPPreference page on const_cast.

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Is const_cast safe?

I can't find much information on const_cast. The only info I could find (on Stack Overflow) is: The const_cast<>() is used to add/remove const(ness) (or volatile-ness) of a variable. This makes me nervous. Could using a const_cast cause…
Mag Roader
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How to use const_cast?

I have a private variable in my Student class defined as: const int studentNumnber; I am trying to write a copy constructor for the Student and I need to cast away the constness to do this. Unfortunately, I don't understand how to use…
Sarah
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Correct usage(s) of const_cast<>

As a common rule, it is very often considered a bad practice to use const_cast<>() in C++ code as it reveals (most of the time) a flaw in the design. While I totally agree with this, I however wonder what are the cases were using const_cast<>() is…
ereOn
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Idiomatic way to create an immutable and efficient class in C++

I am looking to do something like this (C#). public final class ImmutableClass { public readonly int i; public readonly OtherImmutableClass o; public readonly ReadOnlyCollection r; public ImmutableClass(int i,…
lachy
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31
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7 answers

How to call a non-const function within a const function (C++)

I have a legacy function that looks like this: int Random() const { return var_ ? 4 : 0; } and I need to call a function within that legacy code so that it now looks like this: int Random() const { return var_ ? newCall(4) : 0; } The problem…
Grammin
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Why is (int&)0 ill-formed?

According to [expr.cast]/4, a C-style cast tries the following casts in order: const_cast static_cast static_cast followed by const_cast reinterpret_cast reinterpret_cast followed by const_cast The following cast is…
Brian Bi
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Is it allowed to cast away const on a const-defined object as long as it is not actually modified?

Is the following allowed: const int const_array[] = { 42 }; int maybe_inc(bool write, int* array) { if (write) array[0]++; return array[0]; } int main() { return maybe_inc(false, const_cast(const_array)); } In particular, is it OK to…
BeeOnRope
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Convert const char* to QString

I have to use the output of a function of a type const char* and I need to convert it to QString. Note: inside that function, these are lines of code to return the const char* char* ClassA::getData() const{ return const_cast…
Mahmoud Hassan
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2 answers

C++ difference between adding const-ness with static_cast and const_cast of "this" object?

As per Scott Meyers, to prevent repetition of code in the const version of a getter and the non-const version of a getter, call the const version of the method from the non-const version: static_cast(*this).Methodology(); however, in…
Casey
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Why does const_cast remove constness for a pointer but not for a pointer to a const?

I understand that const_cast works with pointers and references. I'm assuming that the input to const_cast should be a pointer or reference. I want to know why it doesn't remove the constness if the input is a pointer/reference to a const int? The…
r18ul
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Am I right in saying that const_cast followed by modification on a ref-to-const bound to a temporary is okay?

I would like to check my understanding and conclusions on this matter. On IRC, it was asked: Is it acceptable to const_cast a const reference that's bound to a temporary object? Translating: he has a ref-to-const bound to a temporary, and he…
Lightness Races in Orbit
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How to convert "pointer to pointer type" to const?

With the following code void TestF(const double ** testv){;} void callTest(){ double** test; TestF(test); } I get this: 'TestF' : cannot convert parameter 1 from 'double **' to 'const double **' I cannot understand why. Why test cannot…
jimifiki
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C++: Why is const_cast evil?

I keep hearing this statement, while I can't really find the reason why const_cast is evil. In the following example: template void OscillatorToFieldTransformer::setOscillator(const SysOscillatorBase &src) { oscillatorSrc =…
The Quantum Physicist
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What is a multilevel pointer?

When reading about const_cast I came across sentences like the following: Only the following conversions can be done with const_cast. In particular, only const_cast may be used to cast away (remove) constness or volatility. 1) Two possibly…
Claudiu
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Modifying element of const std::vector via const_cast

Does the following program have undefined behavior? #include #include struct Foo { const std::vector x; }; int main() { std::vector v = {1,2,3}; auto f = new Foo{v}; const_cast(f->x[1]) = 42; //…
Arch D. Robison
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