【动手出真知】vector reverse & resize_vector reverse resize-优快云博客

本文链接：https://blog.youkuaiyun.com/weixin_44629630/article/details/137873376

本文详细介绍了C++中vector的resize和reserve方法，对比了它们对size和capacity的影响，重点强调了resize会改变大小并可能触发容量扩展，而reserve则只预分配空间但不会改变当前元素数量。

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reverse vs resize
reserve: size-内容不变，指定的reserve参数 > size 变化，<size 不变
resize: 截掉/扩充vector，if（resize参数 < capacity）capacity不变，else{ vector扩容，capacity肯定改变}
capacity vs size
要分清哦

#include <string>
#include <iostream>
#include <vector>

using namespace std;

int main()
{
    std::cout << "\n=======测试resize===\n" << endl;

    vector<int> v1{1, 2, 3, 4, 5};
    std::cout << "v1 source data is : " << "\n";
    for (auto& v : v1)
    {
        std::cout << v << " ";
    }
    std::cout << "\n" << " v1.size=" << v1.size() << " v1.capacity=" << v1.capacity() << endl;

    std::cout << "after resize to 2" << endl;
    v1.resize(2); //尺寸由5改变为2，多余字符被截掉了,只剩下1 2 
    for (auto& v : v1)
    {
        std::cout << v << " ";
    }
    std::cout << " v1.size=" << v1.size() << " v1.capacity=" << v1.capacity() << endl;

    std::cout << "after resize to 12" << endl;
    v1.resize(12, 10000); //尺寸由2改变为12,填充10000
    for (auto& v : v1)
    {
        std::cout << v << ", ";
    }
    std::cout << "\n" << " v1.size=" << v1.size() << " v1.capacity=" << v1.capacity() << endl;
    v1.push_back(88);
    std::cout << "\n" << "v1扩容， v1.size=" << v1.size() << " v1.capacity=" << v1.capacity() << endl;



    std::cout << "\n=======测试reverse===\n" << endl;

    vector<int> v2{1, 2, 3, 4, 5};
    std::cout << "v2 source data is : " << "\n";
    for (auto& v : v2)
    {
        std::cout << v << ", ";
    }
    std::cout << "\n" << " v2.size=" << v2.size() << " v2.capacity=" << v2.capacity() << endl;

    std::cout << "after reserve to 2" << endl;
    v2.reserve(2); // size-内容不变，指定的reserve参数 > size 变化，<size 不变
    for (auto& v : v2)
    {
        std::cout << v << ", ";
    }
    std::cout << "\n" << " v2.size=" << v2.size() << " v2.capacity=" << v2.capacity() << endl;
    //std::cout << "after resize to 12" << endl;
    //v2.resize(12, 0);
    //std::cout << "\n" << " v2.size=" << v2.size() << " v2.capacity=" << v2.capacity() << endl;

    std::cout << "\nafter reserve to 12" << endl;
   
    v2.reserve(12); //size-内容不变，指定的reserve参数 > size 变化，<size 不变
    for (auto& v : v2)
    {
        std::cout << v << ", ";
    }
    std::cout << "\n" << " v2.size=" << v2.size() << " v2.capacity=" << v2.capacity() << endl;

    return 0;
}