1 #include <iostream>
 2 #include <vector>
 3 
 4 using namespace std;
 5 
 6 int main()
 7 {
 8     vector<int> v1(10);
 9 
10     std::cout << "v1 size : " << v1.size() << std::endl;
11     std::cout << "v1 capacity : " << v1.capacity() << std::endl;
12     
13     v1.reserve(20);
14     
15     std::cout << "v1 size : " << v1.size() << std::endl;
16     std::cout << "v1 capacity : " << v1.capacity() << std::endl;
17     
18     return 0;
19 }

此函数用来改变容量大小，运行结果如下：

 

 capacity扩大到了20，size不变。