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When am I supposed to use the default keyword in C++11?

Is it now considered bad to write

struct Foo {

};

and one should write

struct Foo {

  Foo() = default;


};

?

Elizafox
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user695652
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4 Answers4

2

Think of a case when the default constructor will not be provided by the compiler. Then you can use = default to tell the compiler to create a default constructor for you anyway.

Otherwise (and unless you need a special default constructor) there's no reason to specify a default constructor in any way (with or without = default).

In your example, there's no need for the "explicit" = default constructor. It's more a question of style.

Some programmer dude
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  • Thanks, yes in that scenario I understand the benefit of it. But if I really just have above Foo struct, what is now considered clearer omitting the ctr or be more specific and declare it default? – user695652 Jul 29 '16 at 20:17
2

As mentioned here, a default constructor is not generated when you create a constructor with arguments. In those cases, using the default keyword generates the default constructor for the class.

However, consider very carefully whether the object you're dealing with really should have a default constructor; that is, if the default initialisation of other objects is the right thing to do. Keep in mind that POD members are not initalised by default and may contain garbage data without data member initalisers.

Community
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Elizafox
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2

This seems to be an opinion based question. However, it seems that the first option is most commonly used, as the second option is more verbose, and programmers tend not to use default unless a default operation must be deleteed.

DeepCoder
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0

If you provide an explicit non-default constructor, you won't get the compiler provided default. In that case, you may used the default keyword to force the compiler to provide it.

The other case is if you'd like to make sure your default constructor has a specific protection level. For example, you may want to make sure your default constructor is private or protected.

ChrisG0x20
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