Temporary Variable in C++

最新推荐文章于 2023-03-16 12:51:41 发布

airekans

最新推荐文章于 2023-03-16 12:51:41 发布

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分类专栏： C++ 文章标签： include struct c++

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#include "TestTempVar.h"
#include <iostream>

using namespace std;

namespace {
	struct TempClass
	{
		TempClass() : privateCount(count) { ++count; cout << "TempClass " << privateCount <<" ctor" << endl;  }
		~TempClass() { cout << "TempClass " << privateCount << " dtor" << endl; }

		TempClass(const TempClass& t)
		{
			privateCount = count++;
			cout << "TempClass " << privateCount << " copy ctor" << endl;
		}

		TempClass& operator= (TempClass& t)
		{ 
			if (&t != this) 
			{
				privateCount = count++;
			}
			cout << "TempClass " << privateCount << " operator=" << endl;
			return *this;
		}
		
	private:
		static int count;
		int privateCount;
	};
	
	int TempClass::count = 1;

	void testInput(TempClass& t)
	{
		cout << "testInput begin" << endl;
	
		cout << "testInput return" << endl;
	}

	TempClass testReturn()
	{

		cout << "testReturn return" << endl;
		return TempClass();
	}

	TempClass& testReturnRef()
	{

		cout << "testReturn return" << endl;
		return TempClass();
	}
}


void testTemporaryVariable()
{

	cout << "TempClass();" << endl;
	TempClass(); 
	cout << "TempClass(); done" << endl << endl;

	cout << "TempClass& t = TempClass();" << endl;
	TempClass& t = TempClass();
	cout << "TempClass& t = TempClass(); done" << endl << endl;

	cout << "testInput(TempClass());" << endl;
	testInput(TempClass());
	cout << "testInput(TempClass()); done" << endl << endl;

	cout << "TempClass result = testReturn();" << endl;
	TempClass result = testReturn();
	cout << "TempClass result = testReturn(); done" << endl << endl;

	cout << "TempClass& refResult = testReturn();" << endl;
	TempClass& refResult = testReturn();
	cout << "TempClass& refResult = testReturn(); done" << endl << endl;

	cout << "TempClass& refResult2 = testReturnRef();" << endl;
	TempClass& refResult2 = testReturnRef();
	cout << "TempClass& refResult2 = testReturnRef(); done" << endl << endl;
}

直接上代码和输出，大家就明白其中的原理了。

输出：

TempClass();
TempClass 1 ctor
TempClass 1 dtor
TempClass(); done


TempClass& t = TempClass();
TempClass 2 ctor
TempClass& t = TempClass(); done


testInput(TempClass());
TempClass 3 ctor
testInput begin
testInput return
TempClass 3 dtor
testInput(TempClass()); done


TempClass result = testReturn();
testReturn return
TempClass 4 ctor
TempClass result = testReturn(); done


TempClass& refResult = testReturn();
testReturn return
TempClass 5 ctor
TempClass& refResult = testReturn(); done


TempClass& refResult2 = testReturnRef();
testReturn return
TempClass 6 ctor
TempClass 6 dtor
TempClass& refResult2 = testReturnRef(); done


TempClass 5 dtor
TempClass 4 dtor
TempClass 2 dtor