学步园

写了一个小程序，测试了一下vector是如何分配内存的：

Code: Select all

#include <iostream>
#include <vector>
#include <string>
using namespace std;

int main()
{
    vector<string> vec1;
    cout << "Vector size is:  " << vec1.size() << ", capacity is: " << vec1.capacity() << endl;

    for (int i=0; i<30; i++) {
        vec1.push_back("String 1");
        cout << "Vector size is:  " << vec1.size() << ", capacity is: " << vec1.capacity() << endl;
    }

    vec1.reserve(50);
    vec1.push_back("String 2");
    vec1.push_back("String 3");
    cout << "Vector size is:  " << vec1.size() << ", capacity is: " << vec1.capacity() << endl;

    return 0;
}

程序的输出是：

Vector size is: 0, capacity is: 0
Vector size is: 1, capacity is: 1
Vector size is: 2, capacity is: 2
Vector size is: 3, capacity is: 4
Vector size is: 4, capacity is: 4
Vector size is: 5, capacity is: 8
Vector size is: 6, capacity is: 8
Vector size is: 7, capacity is: 8
Vector size is: 8, capacity is: 8
Vector size is: 9, capacity is: 16
Vector size is: 10, capacity is: 16
Vector size is: 11, capacity is: 16
Vector size is: 12, capacity is: 16
Vector size is: 13, capacity is: 16
Vector size is: 14, capacity is: 16
Vector size is: 15, capacity is: 16
Vector size is: 16, capacity is: 16
Vector size is: 17, capacity is: 32
Vector size is: 18, capacity is: 32
Vector size is: 19, capacity is: 32
Vector size is: 20, capacity is: 32
Vector size is: 21, capacity is: 32
Vector size is: 22, capacity is: 32
Vector size is: 23, capacity is: 32
Vector size is: 24, capacity is: 32
Vector size is: 25, capacity is: 32
Vector size is: 26, capacity is: 32
Vector size is: 27, capacity is: 32
Vector size is: 28, capacity is: 32
Vector size is: 29, capacity is: 32
Vector size is: 30, capacity is: 32
Vector size is: 32, capacity is: 50

所以，可以看出，这个平台上，vector的内存分配策略是1, 2, 4, 8, 16, 32......
g++的版本信息是：
g++ (GCC) 3.4.6 20060404 (Red Hat 3.4.6-9)