C++ 如何快速清空vector以及释放vector内存？

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平时我们在写代码时候，有思考过要主动去释放vector的内存吗？

1、对于数据量不大的vector，没有必要自己主动释放vector，一切都交给操作系统。

2、但是对于大量数据的vector，在vector里面的数据被删除后，主动去释放vector的内存就变得很有必要了！

读者可以新建一个控制台程序，把代码运行起来看输出，且看代码：

#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);// 此时检查内存情况
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);// 此时再次检查
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;// 此时容量为0
GetCurProcessMemory(GetCurrentProcess(), wszWorking, wszPeakWorking);// 检查内存
wcout << "Working : " << wszWorking.c_str() << " PeakWorking : " << wszPeakWorking.c_str() << endl;
wcout << "vector size : " << ary.size() << endl;//0
//getchar();
system("pause");
return 0;
}