Value initialization of nested structs does not work properly

Question

I have this struct definitions:

struct inner
{
    int i;
    std::string str;
};

struct outer
{
    inner member[32];
};

Now I want to create a value-initialized instance of outer, so I write

outer o = {};

With GCC, this works just fine: all inner.i are zeroed and all inner.str are empty. But on VS2013, only the inner.str are empty; all inner.i contain garbage i.e. are not properly initialized.

Without the std::string member, the zero-initialization of inner.i works with VS2013.

What does the standard say on this? I always assumed {} initializes everything, either by zeroing or by calling the default constructor. Am I wrong or is this a very bad bug in VS2013?

orlp orlp · Accepted Answer · 2015-11-20T11:03:12

This is simply aggregate initialization:

If the number of initializer clauses is less than the number of members or initializer list is completely empty, the remaining members are initialized by their default initializers, if provided in the class definition, and otherwise (since C++14) by empty lists, which performs value-initialization.

Value initialization means that every element of member is value-initialized, which in turn means that i should be zero.

So yes, this is a VS2013 bug.

Value initialization of nested structs does not work properly

1 Answers