new 语句中类型名后面加一对括号和不加有什么区别
new 语句中类型名后面加一对括号和不加有什么区别
ClearSeve
发布于 2022-02-10 20:50:53
发布于 2022-02-10 20:50:53
问题
如果 Test 就是一个很普通的类，那么下面的两句代码有什么不同么？
Test* test = new Test;
Test* test = new Test();回答
确实会有些差异。
- C++ 1998 中，有两种初始化类型：zero 和 default 初始化。
- C++ 2003 中，多了一种：value 初始化。
假设有以下代码，
struct A { int m; }; // POD
struct B { ~B(); int m; }; // non-POD, compiler generated default ctor
struct C { C() : m() {}; ~C(); int m; }; // non-POD, default-initialising mC++98 中，
- new A – indeterminate value
- new A() – zero-initialize
- new B – default construct (B::m is uninitialized)
- new B() – default construct (B::m is uninitialized)
- new C – default construct (C::m is zero-initialized)
- new C() – default construct (C::m is zero-initialized
C++03 中，
- new A – indeterminate value
- new A() – value-initialize A, which is zero-initialization since it’s a POD.
- new B – default-initializes (leaves B::m uninitialized)
- new B() – value-initializes B which zero-initializes all fields since its default ctor is compiler generated as opposed to user-defined.
- new C – default-initializes C, which calls the default ctor.
- new C() – value-initializes C, which calls the default ctor.
本文参与?腾讯云自媒体分享计划，分享自作者个人站点/博客。
原始发表：2022年1月24日，如有侵权请联系 cloudcommunity@tencent.com 删除
评论
登录后参与评论
推荐阅读
目录