MFC中怎样读取一个JPG文件或BMP位图文件

在MFC中如何读取并显示jpg文件

//picture.h
#pragma once
#include <atlbase.h>
class CPicture {
public:
    CPicture();
    ~CPicture();
    // Load frm various sosurces
    BOOL Load(LPCTSTR pszPathName);
    BOOL Render(CDC* pDC, CRect rc=CRect(0,0,0,0),
    LPCRECT prcMFBounds=NULL) const;
    CSize GetImageSize(CDC* pDC=NULL) const;
    operator IPicture*() { return m_spIPicture; }
    void GetHIMETRICSize(OLE_XSIZE_HIMETRIC& cx, OLE_YSIZE_HIMETRIC& cy) const {
        cx = cy = 0;
        const_cast<CPicture*>(this)->m_hr = m_spIPicture->get_Width(&cx);
        ASSERT(SUCCEEDED(m_hr));
        const_cast<CPicture*>(this)->m_hr = m_spIPicture->get_Height(&cy);
        ASSERT(SUCCEEDED(m_hr));
    }
    void Free() {
        if (m_spIPicture) { m_spIPicture.Release();}
    }

//picture.cpp
#include "stdafx.h"
#include "Picture.h"
#ifdef _DEBUG
#define new DEBUG_NEW
#undef THIS_FILE
static char THIS_FILE[] = __FILE__;
#endif
CPicture::CPicture()
{}
CPicture::~CPicture()
{}

BOOL CPicture::Load(LPCTSTR pszPathName)
{
    CFile file;
    if (!file.Open(pszPathName,CFile::modeRead|CFile::shareDenyWrite))
        return FALSE;
    BOOL bRet = Load(file);
    file.Close();
    return bRet;
}

BOOL CPicture::Render(CDC* pDC, CRect rc, LPCRECT prcMFBounds) const
{
    ASSERT(pDC);
    if (rc.IsRectNull()) {
        CSize sz = GetImageSize(pDC);
        rc.right = sz.cx;
        rc.bottom = sz.cy;
    }
    long hmWidth,hmHeight; // HIMETRIC units
    GetHIMETRICSize(hmWidth, hmHeight);
    m_spIPicture->Render(*pDC, rc.left, rc.top, rc.Width(), rc.Height(),
        0, hmHeight, hmWidth, -hmHeight, prcMFBounds);
    return TRUE;
}

CSize CPicture::GetImageSize(CDC* pDC) const
{
    if (!m_spIPicture)
        return CSize(0,0);
    LONG hmWidth, hmHeight; // HIMETRIC units
    m_spIPicture->get_Width(&hmWidth);
    m_spIPicture->get_Height(&hmHeight);
    CSize sz(hmWidth,hmHeight);
    if (pDC==NULL) {
        CWindowDC dc(NULL);
        dc.HIMETRICtoDP(&sz); // convert to pixels
    } else {
    pDC->HIMETRICtoDP(&sz);
    }
    return sz;
}

//最后在CView类的OnDraw方法中加入调用：
void CShowImageView::OnDraw(CDC* pDC)
{
   CShowImageDoc* pDoc = GetDocument();
   ASSERT_VALID(pDoc);
   CPicture* ppic = new CPicture();
   std::string filename("C:\\mypic.jpg");
   int slength = (int)filename.length() + 1;
   int len = MultiByteToWideChar(CP_ACP, 0, filename.c_str(), slength, 0, 0); 
   wchar_t* buf = new wchar_t[len];
   MultiByteToWideChar(CP_ACP, 0, filename.c_str(), slength, buf, len);
   std::wstring r(buf);
   delete[] buf;
   ppic->Load(r.c_str());
   ASSERT(ppic);
   if (*ppic) {
     CRect rc(0,0,500,500);
     ppic->Render(pDC,rc);
   }
 }
protected:
    CComQIPtr<IPicture>m_spIPicture;
    // ATL smart pointer to IPicture
    HRESULT m_hr;  // last error code
};