A default constructor is a parameterless constructor, often generated by the compiler.
Questions tagged [default-constructor]
817 questions
244
votes
3 answers
How is "=default" different from "{}" for default constructor and destructor?
I originally posted this as a question only about destructors, but now I'm adding consideration of the default constructor. Here's the original question:
If I want to give my class a destructor that is virtual, but is
otherwise the same as what…
KnowItAllWannabe
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227
votes
9 answers
Default constructor with empty brackets
Is there any good reason that an empty set of round brackets (parentheses) isn't valid for calling the default constructor in C++?
MyObject object; // ok - default ctor
MyObject object(blah); // ok
MyObject object(); // error
I seem to type…
Martin Beckett
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202
votes
7 answers
Does the default constructor initialize built-in types?
Does the default constructor (created by the compiler) initialize built-in-types?
Siggi
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189
votes
13 answers
Java default constructor
What exactly is a default constructor — can you tell me which one of the following is a default constructor and what differentiates it from any other constructor?
public Module() {
this.name = "";
this.credits = 0;
this.hours = 0;
}
public…
antanis
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187
votes
14 answers
Kotlin with JPA: default constructor hell
As JPA requires, @Entity classes should have a default (non-arg) constructor to instantiate the objects when retrieving them from the database.
In Kotlin, properties are very convenient to declare within the primary constructor, as in the following…
hotkey
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168
votes
11 answers
Why does the default parameterless constructor go away when you create one with parameters
In C#, C++ and Java, when you create a constructor taking parameters, the default parameterless one goes away. I have always just accepted this fact, but now I've started wondering why.
What is the reason for this behavior? Is it just a "safety…
olagjo
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153
votes
3 answers
Conditions for automatic generation of default/copy/move ctor and copy/move assignment operator?
I want to refresh my memory on the conditions under which a compiler typically auto generates a default constructor, copy constructor and assignment operator.
I recollect there were some rules, but I don't remember, and also can't find a reputable…
oompahloompah
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145
votes
5 answers
Default initialization of std::array?
With C++11 std::array, do I have the guarantee that the syntax std::array x; will default-initialize all the elements of the array ?
EDIT: if not, is there a syntax that will work on all arrays (including zero-sized arrays) to initialize all…
Vincent
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137
votes
12 answers
How to disable warning on Sonar: Hide Utility Class Constructor?
I'm getting this warning on Sonar:
Hide Utility Class Constructor:
Utility classes should not have a public or default constructor
My class:
public class FilePathHelper {
private static String resourcesPath;
public static String…
Oomph Fortuity
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105
votes
4 answers
Creating instance of type without default constructor in C# using reflection
Take the following class as an example:
class Sometype
{
int someValue;
public Sometype(int someValue)
{
this.someValue = someValue;
}
}
I then want to create an instance of this type using reflection:
Type t =…
Aistina
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97
votes
3 answers
When is a private constructor not a private constructor?
Let's say I have a type and I want to make its default constructor private. I write the following:
class C {
C() = default;
};
int main() {
C c; // error: C::C() is private within this context (g++)
// error:…
Barry
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82
votes
8 answers
Should we always include a default constructor in the class?
I have been asked this question by a colleague that should we always include a default constructor in a class? If so, why? If no, why not?
Example
public class Foo {
Foo() { }
Foo(int x, int y) {
...
}
}
I am also interested…
Moon
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72
votes
7 answers
Why do C++ objects have a default destructor?
When I don't declare a constructor for example, the compiler will provide me with a default constructor that will have no arguments and no definition (empty body), and thus, will take no action.
So, if I'm finished with an object for example,…
Simplicity
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71
votes
3 answers
Why won't this compile without a default constructor?
I can do this:
#include
int counter;
int main()
{
struct Boo
{
Boo(int num)
{
++counter;
if (rand() % num < 7) Boo(8);
}
};
Boo(8);
return 0;
}
This will compile…
Zebrafish
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58
votes
3 answers
Is default no-args constructor mandatory for Gson?
Gson user guide states that we should define default no-args constructor for any class to work with Gson properly. Even more, in the javadoc on Gson's InstanceCreator class said that exception will be thrown if we try to deserialize instance of…
raindev
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