C++ Vector Resize函数


Change size

Resizes the container so that it contains ​n​ elements.

If ​n​ is smaller than the current container ​​size​​, the content is reduced to its first ​n​ elements, removing those beyond (and destroying them).

If ​n​ is greater than the current container ​​size​​, the content is expanded by inserting at the end as many elements as needed to reach a size of ​n​. If ​val​ is specified, the new elements are initialized as copies of ​val​, otherwise, they are value-initialized.

If ​n​ is also greater than the current container ​​capacity​​, an automatic reallocation of the allocated storage space takes place.

Notice that this function changes the actual content of the container by inserting or erasing elements from it.


​​void resize (size_type n, value_type val = value_type());​​

改变vector容器的大小。

改变容器的大小使他包含 n n n个元素。




如果 n nn 小于当前容器大小，则内容减少到前n nn个元素，移除后面的元素。
  • 如果 n nn 大于当前容器大小，则在后面插入一些元素至n nn个大小，如果v a l valval被定义则插入v a l valval的复制，否则插入默认值0 00。
  • 如果n nn大于当前容器的容量( c a p a c i t y ) (capacity)(capacity)，则自动进行内容重新分配。

实例

// resizing vector
#include <iostream>
#include <vector>

int main ()
{
  std::vector<int> myvector;

  // set some initial content:
  for (int i=1;i<10;i++) myvector.push_back(i);

  myvector.resize(5);
  myvector.resize(8,100);
  myvector.resize(12);

  std::cout << "myvector contains:";
  for (int i=0;i<myvector.size();i++)
    std::cout << ' ' << myvector[i];
  std::cout << '\n';

  return 0;
}

​结果​

myvector contains: 1 2 3 4 5 100 100 100 0 0 0 0