vector 扩容函数有哪些？

reserve 和 resize。
reserve如果预留的空间，不够则继续分配。
resize如果预留空间不够，也会继续分配内存，并且会调用构造函数。

  1. #include<iostream>
  2. #include<vector>
  3. using namespace std;
  4. int main() {
  5.     vector<int> v1(10);
  6.     cout<<v1.size()<<endl; // 10
  8.     v1.resize(20);
  9.     cout<<v1.size()<<endl; // 20
  11.     v1.reserve(30);
  12.     cout<<v1.size()<<endl; // 20
  13. }

两个vector快速交换赋值

swap，直接交换容器内元素的地址，不会重新构造。

  1. #include <iostream>
  2. #include <vector>
  4. int main ()
  5. {
  6.   std::vector<int> foo (3,100);   // three ints with a value of 100
  7.   std::vector<int> bar (5,200);   // five ints with a value of 200
  10.   std::cout << "foo contains:";
  11.   for (unsigned i=0; i<foo.size(); i++)
  12.     std::cout << ' ' << foo[i];
  13.   std::cout << '\n';
  15.   std::cout << "bar contains:";
  16.   for (unsigned i=0; i<bar.size(); i++)
  17.     std::cout << ' ' << bar[i];
  18.   std::cout << '\n';
  20.   cout<<&foo[0]<<endl;
  21.   foo.swap(bar);
  23.   std::cout << "foo contains:";
  24.   for (unsigned i=0; i<foo.size(); i++)
  25.     std::cout << ' ' << foo[i];
  26.   std::std::cout << '\n';
  28.   std::cout << "bar contains:";
  29.   for (unsigned i=0; i<bar.size(); i++)
  30.     std::cout << ' ' << bar[i];
  31.   std::cout << '\n';
  32.   std::cout<<&bar[0]<<endl;
  33.   return 0;
  34. }
  1. foo contains: 100 100 100
  2. bar contains: 200 200 200 200 200
  3. 0x7ff040400020
  4. foo contains: 200 200 200 200 200
  5. bar contains: 100 100 100
  6. 0x7ff040400020