static variable construction in C++
How do compilers know how to correctly handle this code?
struct Foo
{
int bar;
Foo()
{
bar = 3;
}
Foo& operator=(const Foo& other)
{
bar = other.bar;
return *this;
}
int SetBar(int newBar)
{
return bar = newBar;
}
};
static Foo baz;
static Foo someOtherBaz = baz;
static int placeholder = baz.SetBar(4);
What wou开发者_如何转开发ld the final value of someOtherBaz.bar
be?
The value of someOtherBaz.bar
would be 3.
Static objects within a translation unit are constructed in the order they appear within the TU (note, there is no defined order of static object in different translation units).
- First,
baz
will be constructed with the default constructor. This will setbaz.bar
to 3. - Next
someOtherBaz
will be constructed via the copy constructor. Since no copy constructor was defined, a default copy constructor will be used which will just copy each field. SosomeOtherBaz.bar
will be given the value of 3. - Finally, to construct
placeholder
,baz.SetBar
will be called which will also change the value ofbaz
(but notsomeOtherBaz
since they are independent objects; while you createdsomeOtherBaz
based on the value ofbaz
, they are different objects so can change independently).
So, at the end, you'll have:
baz.bar: 4
someOtherBaz.bar: 3
placeholder: 4
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