请你回答一下STL里resize和reserve的区别？

“`” resize()：改变当前容器内含有元素的数量(size())，eg: vectorv; v.resize(len);v的size变为len,如果原来v的size小于len，那么容器新增（len-size）个元素，元素的值为默认为0.当v.push_back(3);之后，则是3是放在了v的末尾，即下标为len，此时容器是size为len+1；

<pre><code>#include <iostream>#include <vector>using namespace std;int main() { vector<int> a; a.reserve(100); a.resize(50); cout<<a.size()<<"" ""<<a.capacity()<<endl; //50 100 a.resize(150); cout<<a.size()<<"" ""<<a.capacity()<<endl; //150 200 a.reserve(50); cout<<a.size()<<"" ""<<a.capacity()<<endl; //150 200 a.resize(50); cout<<a.size()<<"" ""<<a.capacity()<<endl; //50 200 }</code></pre>

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