CODEWITHSUNDEEP
c++c++11
Stefan Weiser
Stefan Weiser

Reputation: 2292

Non-static data member initialization

Are there any differences between the following three structure definitions according to the C++ standard?

struct Foo
{
    int a;
};

struct Foo
{
    int a{};
};

struct Foo
{
    int a{0};
};

The last two are C++11.

Upvotes: 10

Views: 1321

Answers (3)

Praetorian
Praetorian

Reputation: 109119

Given the first definition, if you create an instance of Foo with automatic storage duration, a will be uninitialized. You can perform aggregate initialization to initialize it.

Foo f{0};  // a is initialized to 0

The second and third definitions of Foo will both initialize the data member a to 0.

In C++11, neither 2 nor 3 are aggregates, but C++14 changes that rule so that they both remain aggregates despite adding the brace-or-equal-initializer.

Upvotes: 9

Konstantin Myachin
Konstantin Myachin

Reputation: 11

First one is POD type. Member a is initialized by 0.

Upvotes: 1

Mohit Jain
Mohit Jain

Reputation: 30489

struct Foo
{
    int a;
}bar;

bar.a is uninitialized if not in global scope or not-static.

struct Foo
{
    int a{};
}bar;

bar.a is initialized to 0

struct Foo
{
    int a{0};
}bar;

bar.a is initialized to 0

So constructs 2 and 3 are same. 1 is different.

For more details, you may want to read Initialization and Class Member Initialization

Upvotes: 4

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