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* [Bug c++/63717] New: Value-initialization performs defaut-initialization when =default is outside the class declaration
@ 2014-11-02 22:50 morwenn29 at hotmail dot fr
2014-11-03 0:58 ` [Bug c++/63717] " morwenn29 at hotmail dot fr
2014-11-03 9:16 ` morwenn29 at hotmail dot fr
0 siblings, 2 replies; 3+ messages in thread
From: morwenn29 at hotmail dot fr @ 2014-11-02 22:50 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63717
Bug ID: 63717
Summary: Value-initialization performs defaut-initialization
when =default is outside the class declaration
Product: gcc
Version: 4.9.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: morwenn29 at hotmail dot fr
I have this minimal test case:
struct foo
{
unsigned value;
foo();
foo(unsigned value):
value(value)
{}
};
foo::foo()
= default;
int main()
{
foo bar{};
}
In this test case, foo bar{}; should zero-initialize bar and thus
zero-initialize value (see http://stackoverflow.com/q/26699720/1364752 for a
discussion about that). However, value is sometimes initialized with garbage
instead of being initialized with 0. Here is the assembly produced by the
example above:
push %ebp
mov %esp,%ebp
and $0xfffffff0,%esp
sub $0x10,%esp
call 0x402060 <__main>
lea 0xc(%esp),%eax
mov %eax,%ecx
call 0x401610 <foo::foo()>
mov $0x0,%eax
leave
ret
As you can see, the default constructor of foo is called, but value is not
zero-initialized here. However, if we move = default in the class declaration:
struct foo
{
unsigned value;
foo() = default;
foo(unsigned value):
value(value)
{}
};
foo::foo()
= default;
int main()
{
foo bar{};
}
Then, the produced assembly is not the same anymore and value is properly
zero-initialized as expected:
push %ebp
mov %esp,%ebp
and $0xfffffff0,%esp
sub $0x10,%esp
call 0x402050 <__main>
movl $0x0,0xc(%esp) ; init value (?)
mov $0x0,%eax
leave
ret
I am not really good at reading assembly but I fixed my problem by moving the
=default into the class instead separating the declaration of the default
constructor and its definition. If I correctly read both the standard and the
assembly, I am pretty sure that this is a GCC bug.
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug c++/63717] Value-initialization performs defaut-initialization when =default is outside the class declaration
2014-11-02 22:50 [Bug c++/63717] New: Value-initialization performs defaut-initialization when =default is outside the class declaration morwenn29 at hotmail dot fr
@ 2014-11-03 0:58 ` morwenn29 at hotmail dot fr
2014-11-03 9:16 ` morwenn29 at hotmail dot fr
1 sibling, 0 replies; 3+ messages in thread
From: morwenn29 at hotmail dot fr @ 2014-11-03 0:58 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63717
--- Comment #1 from Morwenn <morwenn29 at hotmail dot fr> ---
I forgot to remove the outside-class =default in the second example, it should
be:
struct foo
{
unsigned value;
foo() = default;
foo(unsigned value):
value(value)
{}
};
int main()
{
foo bar{};
}
Sorry for that.
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug c++/63717] Value-initialization performs defaut-initialization when =default is outside the class declaration
2014-11-02 22:50 [Bug c++/63717] New: Value-initialization performs defaut-initialization when =default is outside the class declaration morwenn29 at hotmail dot fr
2014-11-03 0:58 ` [Bug c++/63717] " morwenn29 at hotmail dot fr
@ 2014-11-03 9:16 ` morwenn29 at hotmail dot fr
1 sibling, 0 replies; 3+ messages in thread
From: morwenn29 at hotmail dot fr @ 2014-11-03 9:16 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63717
Morwenn <morwenn29 at hotmail dot fr> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution|--- |INVALID
--- Comment #2 from Morwenn <morwenn29 at hotmail dot fr> ---
Not a bug actually, sorry for that (that makes two "sorry" in two messages). I
read again [dcl.fct.def.default] and it appears that I was wrong; I totally
missed the "first declaration" part in the following statement:
A function is user-provided if it is user-declared and not explicitly defaulted
or
deleted on its first declaration.
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2014-11-03 9:16 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
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2014-11-02 22:50 [Bug c++/63717] New: Value-initialization performs defaut-initialization when =default is outside the class declaration morwenn29 at hotmail dot fr
2014-11-03 0:58 ` [Bug c++/63717] " morwenn29 at hotmail dot fr
2014-11-03 9:16 ` morwenn29 at hotmail dot fr
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