c – 新分配的std :: vector元素是否初始化为0？

[C++11: 23.3.6.3/9]: void resize(size_type sz);

Effects: If sz <= size(),equivalent to erase(begin() + sz,end());. If size() < sz,appends sz - size() value-initialized elements to the sequence.

对于int和long,这意味着0：

[C++11: 8.5/7]: To value-initialize an object of type T means:

• if T is a (possibly cv-qualified) class type (Clause 9) with a user-provided constructor (12.1),then the default constructor for T is called (and the initialization is ill-formed if T has no accessible default constructor);
• if T is a (possibly cv-qualified) non-union class type without a user-provided constructor,then the object is zero-initialized and,if T’s implicitly-declared default constructor is non-trivial,that constructor is called.
• if T is an array type,then each element is value-initialized;
• otherwise,the object is zero-initialized.

An object that is value-initialized is deemed to be constructed and thus subject to provisions of this International Standard applying to “constructed” objects,objects “for which the constructor has completed,” etc.,even if no constructor is invoked for the object’s initialization.

但请注意,这并不是在向量的末尾讨论“保留”空间.此空间不包含任何有效元素,零初始化或其他.此答案和标准措辞仅讨论在执行调整大小时未获得新元素的显式值时获得的元素.