c++ - 向量的两个特征之间的区别

Question

有什么区别：

std::vector::erase

和

std::vector::clear

我想要做的是摆脱所有元素，位置，包括内存地址并且没有抛出异常。

vector<array<double,1000>> S1(1000);

最后我想摆脱 1000*2 创建的内存地址。

Answer 1

erase gets rid of elements selectively by position. clear gets rid of all elements unconditionally, and can be considered syntactic sugar for a call to v.erase(v.begin(),v.end());

Answer 2

The only sure way to release the memory that I can think of is to swap with a temporary vector:

vector<array<double,1000>> S1(1000);
...
vector<array<double,1000>>().swap(S1);

Although this might look strange at first, it is a known, widely used idiom.

In C++11, moving from the original vector might be an option, although it is not guaranteed to clear the memory or even clear the vector (I cannot think of a reason why an implementation wouldn't do that though):

{
  vector<array<double,1000>> tmp(std::move(S1));
} // tmp dies on exiting scope, memory is cleared

Altenratively, a call to std::vector::shrink_to_fit could result in memory de-allocation, but there are no guarantees:

S1.clear();
S1.shrink_to_fit();

Answer 3

擦除可让您指定开始和结束位置，而清除则清除整个向量。

http://www.cplusplus.com/reference/vector/vector/erase/

http://www.cplusplus.com/reference/vector/vector/clear/

Answer 4

v.erase(v.begin(),v.end()) 等价于 v.clear() 其中 v 是任何向量的对象。这里 clear 将用于删除所有向量元素，但 erase 可以用来删除任何特定元素或元素范围。

Answer 5

该函数clear()清空向量。该函数erase()删除选择性元素（有几个重载）。erase(v.begin(), v.end());相当于调用clear();. 创建的内存仍将保留以备将来使用。如果你想确保释放所有这些内存，那么如果你有 C++11 编译器，请调用v.clear();and then 。v.shrink_to_fit()（实际上并不能保证内存会被释放，这只是一个请求，但我不知道有任何编译器不会释放内存。）如果您不符合 C++11，请使用替代方案std::vector<std::array<double,1000>>().swap(v);. 这被称为缩小以适应成语。