为什么在这里没有调用构造函数（Visual Studio C ++ 2013）？ [英] Why is there no calling of the constructor here (Visual Studio C++ 2013)?

问题描述

我在visual studio 2013中有一个简短的代码段来测试我正在编写的控件：

I have a short code segment here with visual studio 2013 to test my controls that I am writing:

//void CbmpLoadView::OnRButtonDown(UINT nFlags, CPoint point)
void CbmpLoadView::OnRButtonDown(UINT nFlags, CPoint point)
{

	TestCDCDirectControls t1();
	int x2;
	x2 = 2;  // break pont set here
}

//TestCDCDirectControls.h

class TestCDCDirectControls : public CDCDirectControls
	{
	public:
		CDCDirectControls CDC_c1;

		TestCDCDirectControls(); //declare the initializer
		inline ~TestCDCDirectControls(){ return; };  // default destructor just return
	};

和

and

//TestCDCDirectControls.cpp

#include "stdafx.h"

#include "CDCDirectControls.h"
#include "TestCDCDirectControls.h"

/*This class is used to test the CDCDirectControls to make sure that they are working.  When an instance is created, it tests the CDC Direct Controls */
TestCDCDirectControls::TestCDCDirectControls(){
		int x;   
		x = 1; //I have the debug break point set here
		return;
};

我在TestCDCDirectControls上面的行中设置了调试点.cpp停在那里。但似乎永远不会调用构造函数，因为当我按下鼠标右键时，它会在调试行停止：

I have the debug point set at the line above in "TestCDCDirectControls.cpp" to stop there. But it seems that the constructor is never called, because when I press the right mouse button, it stops at the debug line:

x2 = 2;

但它永远不会停在调试行：

But it never stops at the debug line:

x=1;

发生了什么，如何让它停在调试行

What is going on, and how can I get it to stop at the debug line

x=1;

？





答案：我调整了这样的代码，一切都按预期工作，在t1内创建一个方法，以便它做了一些事情。我很高兴这个问题相对容易通过。

?


Answer: I adjusted the code like this and everything worked as expected, creating a method inside t1 so that it did something. I am glad that issue was relatively easy to get through.

//void CbmpLoadView::OnRButtonDown(UINT nFlags, CPoint point)
void CbmpLoadView::OnRButtonDown(UINT nFlags, CPoint point)
{

	TestCDCDirectControls t1;
	int x2;
	x2 = 2;
	x2 = t1.ReturnX1();

}

特别需要创建方法;如果我将方法ReturnX1注释掉，那么构造函数不再被调用（至少没有达到调试点）！

Creating the method was specifically required; if I commented the method ReturnX1 out, then the constructor was not called again (at least the debug point was not reached)!

推荐答案

因为

Because

TestCDCDirectControls t1();

声明一个名为t1的函数，返回TestCDCDirectControls类型的值。另请参见标准C ++ [ ^ ]。

因为声明了一个函数不会实例化任何东西，也不会执行任何构造函数。



另一方面，在你的第二次试验中

declares a function named "t1" returning a value of type "TestCDCDirectControls". See also Standard C++[^].
And because declaring a function does not instantiate anything, also no constructor will be executed.

On the otherhand in your second Trial

TestCDCDirectControls t1;

确实定义了类型为TestCDCDirectControls的变量t1，因此将执行TestCDCDirectControls的构造函数



所以最后不要再添加x2 = t1.ReturnX1（）;是解决方案，只需以正确的方式定义变量t1即可解决您的问题。



对不起我的英语，无论如何我希望这会有所帮助。

really defines a variable "t1" of type "TestCDCDirectControls" and therefore constructor of "TestCDCDirectControls" will be executed

So finally not your Addition of "x2 = t1.ReturnX1();" was the solution, simply defining the variable "t1" in a correct way solved your issue.

Sorry for my english, anyway I hope this helps.

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