vector笔记

vector笔记 

Posted on  10/06/2012 | 被浏览了  339 次

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#include <cstdio> #include <vector>   using namespace std;   int main() {      vector < int > a;      printf ( "size:%d capacity:%d\n" , a.size(), a.capacity());      a.push_back(1);      printf ( "size:%d capacity:%d\n" , a.size(), a.capacity());      a.push_back(1);      printf ( "size:%d capacity:%d\n" , a.size(), a.capacity());      a.push_back(1);      printf ( "size:%d capacity:%d\n" , a.size(), a.capacity());      a.push_back(1);      printf ( "size:%d capacity:%d\n" , a.size(), a.capacity());      a.push_back(1);      printf ( "size:%d capacity:%d\n" , a.size(), a.capacity());      a.push_back(1);      printf ( "size:%d capacity:%d\n" , a.size(), a.capacity());      a.push_back(1);      printf ( "size:%d capacity:%d\n" , a.size(), a.capacity());      a.push_back(1);      printf ( "size:%d capacity:%d\n" , a.size(), a.capacity());      a.clear();      printf ( "size:%d capacity:%d\n" , a.size(), a.capacity()); }

输出：

size:0 capacity:0
size:1 capacity:1
size:2 capacity:2
size:3 capacity:4
size:4 capacity:4
size:5 capacity:8
size:6 capacity:8
size:7 capacity:8
size:8 capacity:8
size:0 capacity:8

验证2个事实：

1.vector每次容量不够的时候，会申请一个双倍的内存空间，然后被旧的数据拷的新的地方，并释放旧内存。

2.vector在clear之后（或erase很多元素之后），并不会释放内存。