CPen pOldPen=pDC->SelectObject(&Pen);和CPen pOldPen=&Pen有什么区别

elvavadn 2012-05-03 08:57:14

CDC *DC =GDC（）；
CPen Pen;
Pen.CreatePen(PS_SOLID,1,RGB(255,0,0));
CPen *pOldPen=pDC->SelectObject(&Pen);

问题如下：

CPen *pOldPen=pDC->SelectObject(&Pen);
和
CPen *pOldPen=&Pen;

有什么区别 ,为什么不直接用 CPen *pOldPen=&Pen;

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song382364283 2012-07-08

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CPen *pOldPen=pDC->SelectObject(&Pen);
这句是返回旧画笔
CPen *pOldPen=&Pen;
是新画笔存储

cadinfo 2012-05-08

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呵呵，论坛小弟弟

smilenot 2012-05-03

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你没看懂程序的目的啦
看懂了就不会有这样的疑问了

mabaoyes 2012-05-03

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2楼说的准确：
CPen *pOldPen=pDC->SelectObject(&Pen);//把画笔（Pen）与DC关联，并返回原来与DC关联的画笔。
而CPen *pOldPen=&Pen; 只是取Pen,功能完全不同。

Eleven 2012-05-03

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SelectObject(&pen);返回先前的CPen类对象的指针
A pointer to the object being replaced. This is a pointer to an object of one of the classes derived from CGdiObject, such as CPen, depending on which version of the function is used. The return value is NULL if there is an error. This function may return a pointer to a temporary object. This temporary object is only valid during the processing of one Windows message. For more information, see CGdiObject::FromHandle.

zhouzhipen 2012-05-03

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CPen *pOldPen=pDC->SelectObject(&Pen);//把画笔（Pen）与DC关联，并返回原来与DC关联的画笔。
所以pDC->SelectObject(&Pen)返回的并不是&Pen，而是原来与之关联的画笔。

BombZhang 2012-05-03

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CPen *pOldPen=pDC->SelectObject(&Pen);
SelectObject返回的是前面正在使用的Pen，所以叫oldpen。也就是说SelectObject用参数Pen替换了原来使用的pen，替换后把原来使用的pen返回备份，当新的pen不再使用后再用SelectObject替换回来。

三条猫 2012-05-03

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CPen *pOldPen=pDC->SelectObject(&Pen);
是把当前设备描述表使用的pen返回给你,并设置你传入的pen.

向立天 2012-05-03

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系统中总会有一个画笔
当你选入新笔的时候会把老笔返回
用完后你要把老笔回复
这样别的程序会继续使用
否则会造成混乱

用C++写的一个简单的界面演示系统 void CMiniDrawDoc::AddFigure (CFigure *PFigure) { m_FigArray.Add (PFigure); SetModifiedFlag (); } CFigure *CMiniDrawDoc::GetFigure (int Index) { if (Index m_FigArray.GetUpperBound ()) return 0; return (CFigure *)m_FigArray.GetAt (Index); } int CMiniDrawDoc::GetNumFigs () { return m_FigArray.GetSize (); } void CMiniDrawDoc::DeleteContents() { // TODO: Add your specialized code here and/or call the base class int Index = m_FigArray.GetSize (); while (Index--) delete m_FigArray.GetAt (Index); m_FigArray.RemoveAll (); CDocument::DeleteContents(); } void CMiniDrawDoc::OnEditClearAll() { // TODO: Add your command handler code here DeleteContents (); UpdateAllViews (0); SetModifiedFlag (); } void CMiniDrawDoc::OnUpdateEditClearAll(CCmdUI* pCmdUI) { // TODO: Add your command update UI handler code here pCmdUI->Enable (m_FigArray.GetSize ()); } void CMiniDrawDoc::OnEditUndo() { // TODO: Add your command handler code here int Index = m_FigArray.GetUpperBound (); if (Index > -1) { delete m_FigArray.GetAt (Index); 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PDC->SelectObject (POldBrush); }

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void CCube1View::cube_def( ) { int i,j; CDC *pDC=GetDC(); CPen pen; pen.CreatePen(PS_SOLID,1,RGB(255,255,255)); CPen *poldpen=pDC->SelectObject(&pen); for(i=0;iMoveTo(b[i].x,b[i].y); for(j=1;jLineTo(b[i+j].x,b[i+j].y); pDC->LineTo(b[i].x,b[i].y); } for(i=0;iMoveTo(b[i].x,b[i].y); pDC->LineTo(b[i+4].x,b[i+4].y); }

背景类源代码： CClockBackground::~CClockBackground() { } void CClockBackground::Draw(CDC *pDC) { CPen penMain(PS_SOLID, 1, m_crMain), penOther(PS_SOLID, 1, m_crOther); CBrush brMain(m_crMain), brOther(m_crOther); CPen *pOldPen = pDC->SelectObject(&penOther); CBrush *pOldBrush = pDC->SelectObject(&brMain); CPoint ptCenter = m_rcRegion.CenterPoint(); int nRadius = m_nRadius - 8; for(int i = 0; i < 60; i++) { CPoint ptEnd = ptCenter; ptEnd.Offset((int)(nRadius * sin(2*PI*(i%60)/60)), (int)(-nRadius*cos(2*PI*(i%60)/60))); CRect rcDot(-2, -2, 2, 2); rcDot.OffsetRect(ptEnd); pDC-> Ellipse(rcDot); } pDC -> SelectObject(&penMain); pOldBrush = pDC -> SelectObject(&brOther); for(i = 0; i < 12; i++) { CPoint ptEnd = ptCenter; double fRadian = 2 * PI * (i % 12) / 12; ptEnd.Offset((int)(nRadius)*sin(fRadian), (int)(-nRadius*cos(fRadian))); CRect rcDot(-3, -3, 3, 3); rcDot.OffsetRect(ptEnd); pDC->Rectangle(rcDot); } pDC -> SelectObject(pOldPen); pDC -> SelectObject(pOldBrush); }

VC++绘图程序设计实例 void CMyView::DrawPolyfaces() {// 此函数用来绘出整个多个多面体立体图形 int StNo, I, J, P, Stvj; CPoint point[LimAt]; CRgn rgn; CPen pen(PS_SOLID,2,(COLORREF)1); CDC*pDC=GetDC(); CPen *pOldPen=pDC->SelectObject(&pen); CBrush brush(RGB(255,255,255)); // CBrush brush(RGB(255,0,0)); // CBrush* pOldBrush=pDC->SelectObject(&brush); for ( I = 1; I <= VisFcNo; ++I ) { P = Pri[I]; TestOk = InvisibleFace(P); // 返回平面可见性检测标志 if ( TestOk==0 ) // 如果可见 { StNo = Fc[P][0]; // CPoint point[StNo]; for ( J = 1; J <= StNo; J++ ) {// 构造调用函数fillpoly()所用的顶点数组 Stvj = Fc[P][J]; point[J-1].x = StSn[Stvj][0]; point[J-1].y = StSn[Stvj][1]; } point[StNo]=point[0]; pDC->Polyline(point,StNo+1); // 画出多边形 rgn.CreatePolygonRgn(point,StNo+1,ALTERNATE); //多边形填充 pDC->FillRgn(&rgn,&brush); rgn.Detach(); if ( Atinv[P]==1 ) EraseInvisibleedge(P); // 擦除不可见边 } } pDC->SelectObject(pOldPen); ReleaseDC(pDC);

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