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### Preamble
C++ initializes objects in three stages:
1. Optionally, zero-initializes the object fields.
2. Member-initializes fields that are explicitly set.
3. If applicable, calls a constructor.
The following expressions:
x = new T[N];
x = new T;
T x;
only member-initialize and call a default constructor. Stage 1 is skipped,
because () braces are omitted.
This is known as default-initialization.
Apart from Stage 2, the following:
x = new T[N]();
x = new T();
const T &x = T();
Is known as value-initialization:
If no default constructor is present, infer zero-initialization.
Otherwise, the default constructor is called.
Note that it's not possible to write `T x();`, as it is ambiguous to a function
call.
Since C++11, it's also possible to zero initialize objects with '{}' braces:
x = new T[N]{};
x = new T{};
T x{};
This also both zero-initializes and calls a default constructor.
There is no much difference in between empty-braced () and {}. Both call a
default constructor or initializer-list constructor, when available. Having both
constructors is ambiguous.
Scalars (i.e. fundamental data types) and POD types have no constructor.
Therefore, stage 2 for them is skipped.
Other than that, there is no much difference in the result
Exambles:
new char[123] -- would return an uninitialized array of char.
new char[123]() -- forces zero-initialization
new char[123]{} -- forces zero-initialization
new char[123]{123} -- forces zero-initialization, and also value-initializes
the first element to 123
struct A {
int x = 0xaf;
int y;
}
All of the following:
A a;
A *a = new A;
A *a = new A[123];
Causes member A::x be initialized to 0xaf, since it happens at
value-initialization stage. A::y is left uninitialized.
A *a = new A[123] {};
and other similars result in {.x=0xaf, .y=0}.
### In this commit
Change all the calls to thd->calloc() to new(thd) T[N]{}, or new(thd) T{}.
POD types will be zero-initialized, so a special attention should be put to
classes with default constructors.
Among all uses, two cases of interest were found:
1. TABLE_LIST: has a default constructor TABLE_LIST() = default. This infers
zero-initialization behavior (i.e. as if there's no constructor).
2. USER_AUTH: has a default constructor, that initializes all fields. Strings
are initialized to "", which is fine.
3. Security_context: had a custom default constructor, initializing only two
fields. It was removed, and fields are made member-initialized.
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|---|---|---|
| .. | ||
| mysql-test/storage_engine | ||
| CMakeLists.txt | ||
| ha_myisammrg.cc | ||
| ha_myisammrg.h | ||
| myrg_close.c | ||
| myrg_create.c | ||
| myrg_def.h | ||
| myrg_delete.c | ||
| myrg_extra.c | ||
| myrg_info.c | ||
| myrg_locking.c | ||
| myrg_open.c | ||
| myrg_panic.c | ||
| myrg_queue.c | ||
| myrg_range.c | ||
| myrg_records.c | ||
| myrg_rfirst.c | ||
| myrg_rkey.c | ||
| myrg_rlast.c | ||
| myrg_rnext.c | ||
| myrg_rnext_same.c | ||
| myrg_rprev.c | ||
| myrg_rrnd.c | ||
| myrg_rsame.c | ||
| myrg_static.c | ||
| myrg_update.c | ||
| myrg_write.c | ||