C++ 如何快速清空vector以及釋放vector內存？

平時我們在寫代碼時候，有思考過要主動去釋放vector的內存嗎？

1、對於數據量不大的vector，沒有必要自己主動釋放vector，一切都交給操作系統。

2、但是對於大量數據的vector，在vector里面的數據被刪除后，主動去釋放vector的內存就變得很有必要了！

 

讀者可以新建一個控制台程序，把代碼運行起來看輸出，且看代碼：

 

#include <iostream>
#include <vector>
#include <string>
#include <Windows.h>
#include <Psapi.h>
#pragma comment(lib, "Psapi.lib")

using namespace std;

//GetCurPorcessMemory
bool GetCurProcessMemory(HANDLE handle, std::wstring& workingSize, std::wstring& peakWorkingSize)
{
    //HANDLE handle = GetCurrentProcess();
    PROCESS_MEMORY_COUNTERS pmc;
    if (GetProcessMemoryInfo(handle, &pmc, sizeof(pmc)))
    {
        int size = pmc.WorkingSetSize/1024;
        wchar_t buf[10] = {0};
        _ltow(size, buf, 10);
        workingSize = std::wstring(buf);

        size = pmc.PeakWorkingSetSize/1024;
        _ltow(size, buf, 10);
        peakWorkingSize = std::wstring(buf);

        return true;
    }
    return false;
}

int _tmain(int argc, _TCHAR* argv[])
{
    std::wstring wszWorking, wszPeakWorking;
    vector<string> ary;

    for (int i=0; i<1000000; i++)
    {
        ary.push_back("hello vector");
    }

    wchar_t wch;
    wcin >> wch;

    GetCurProcessMemory(GetCurrentProcess(), wszWorking, wszPeakWorking);// 此時檢查內存情況
    wcout << "Working : " << wszWorking.c_str() << " PeakWorking : " << wszPeakWorking.c_str() << endl;

    wcin >> wch;

    //
    ary.clear();
    wcout << "vector clear" << endl;
    wcout << "vector capacity " << ary.capacity() << endl;
    GetCurProcessMemory(GetCurrentProcess(), wszWorking, wszPeakWorking);// 此時再次檢查
    wcout << "Working : " << wszWorking.c_str() << " PeakWorking : " << wszPeakWorking.c_str() << endl;

    wcin >> wch;
    //vector<string>(ary).swap(ary);
    ary.swap(vector<string>(ary));
    wcout << "vector swap" << endl;
    wcout << "vector capacity " << ary.capacity() << endl;// 此時容量為0
    GetCurProcessMemory(GetCurrentProcess(), wszWorking, wszPeakWorking);// 檢查內存
    wcout << "Working : " << wszWorking.c_str() << " PeakWorking : " << wszPeakWorking.c_str() << endl;

    wcout << "vector size : " << ary.size() << endl;//0

    //getchar();
    system("pause");

    return 0;
}