我应该总是在函数末尾调用 vector clear() 吗?
我有一些使用像这样的向量的简单函数(伪代码):
I have some simple function that uses vector like this (pseudo code):
void someFunc(void) {
std::vector<std::string> contentVector;
// here are some operations on the vector
// should I call the clear() here or this could be ommited ?
contentVector.clear();
}
我应该调用 clear() 还是可以省略?
Should I call the clear() or this could be ommited ?
推荐答案
如果我们看看 cppreference.com std::vector::~vector 的条目说:
If we look at the cppreference.com entry for std::vector::~vector it says:
破坏容器.调用元素的析构函数并释放已使用的存储空间.请注意，如果元素是指针，则指向的对象不会被销毁.
Destructs the container. The destructors of the elements are called and the used storage is deallocated. Note, that if the elements are pointers, the pointed-to objects are not destroyed.
所以不，您不必调用clear.
如果我们要查看草案标准，我们要看看23.2.1一般容器要求4段，它说:
If we want to go to the draft standard, we have to look at section 23.2.1 General container requirements paragraph 4 which says:
在表 96 和 97 中，X 表示包含 T 类型对象的容器类，a 和 b 表示 X 类型的值，[...]
In Tables 96 and 97, X denotes a container class containing objects of type T, a and b denote values of type X,[...]
然后查看具有以下表达式条目的表 96 ― 容器要求:
and then look at Table 96 ― Container requirements which has the following expression entry:
(&a)->~X()
以及以下注意事项:
注意:析构函数应用于a的每个元素；所有内存都被释放.
note: the destructor is applied to every element of a; all the memory is deallocated.
更新
这是 RAII 的实际操作，正如 Bjarne Stroustrup 在为什么 C++ 不提供finally"构造?:
This is RAII in action and as Bjarne Stroustrup says in Why doesn't C++ provide a "finally" construct?:
因为 C++ 支持一种几乎总是更好的替代方法:资源获取即初始化"技术(TC++PL3 第 14.4 节).基本思想是用一个本地对象来表示一个资源，这样本地对象的析构函数就会释放该资源.这样程序员就不会忘记释放资源了.
Because C++ supports an alternative that is almost always better: The "resource acquisition is initialization" technique (TC++PL3 section 14.4). The basic idea is to represent a resource by a local object, so that the local object's destructor will release the resource. That way, the programmer cannot forget to release the resource.
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