前言：在用mfc框架编写应用的时候，如果注意，你会发现在App应用类的InitInstance()函数中，初始化时总有一个 SetRegistryKey("String");  这是什么函数呢，设置记录字符串，不明觉厉，于是用心去查了一下，分享给大家。

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总起：其实很明了，如果你的应用需要使用注册表，则它为你提供了很便利的方法，当然如果不使用系统注册表，这句可以注释掉。

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SetRegistryKey

Causes application settings to be stored in the registry instead of .INI files.

设置MFC程序的注册表访问键，并把读写 ini 文件的成员函数映射到读写注册表。只要调用一下 SetRegistryKey 并指定注册表键值，那么下面6个成员函数，就被映射到进行注册表读取了（有点类似指向切换）

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WriteProfileBinary	Writes binary data to an entry in the application's .INI file.
WriteProfileInt	Writes an integer to an entry in the application's .INI file.
WriteProfileString	Writes a string to an entry in the application's .INI file.

GetProfileBinary	Retrieves binary data from an entry in the application's .INI file.
GetProfileInt	Retrieves an integer from an entry in the application's .INI file.
GetProfileString	Retrieves a string from an entry in the application's .INI file.

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具体用法：

CString strUserName,strPassword;

WriteProfileString("LogInfo","UserName",strUserName); //向注册表HKEY_CURRENT_USER//software//boli's app//LogInfo//分支下写入 UserName 字符串行键值~

WriteProfileString("LogInfo","Password",strPassword);//同上

 strUserName = GetProfileString("LogInfo","UserName");// 这里是读取HKEY_CURRENT_USER//software//boli's app//LogInfo//分支下的 UserName 字符串键值到 strUserName

 strPassword =  GetProfileString("LogInfo","Password"); 

// 如果不是在CWinApp 派生的类中读写注册表，可以直接用：

 strUserName = theApp.GetProfileString("LogInfo","UserName");

 strPassword = theApp.GetProfileString("LogInfo","Password");

// 或 

 strUserName = AfxGetApp()->GetProfileString("LogInfo","UserName");

下面是MFC中的具体实现代码，可以看看是如何实现的：

// CWinApp Settings Helpers

#ifdef AFX_INIT_SEG

#pragma code_seg(AFX_INIT_SEG)

#endif

void CWinApp::SetRegistryKey(LPCTSTR lpszRegistryKey)

{

 ASSERT(m_pszRegistryKey == NULL);

 ASSERT(lpszRegistryKey != NULL);

 ASSERT(m_pszAppName != NULL);

 BOOL bEnable = AfxEnableMemoryTracking(FALSE);

 free((void*)m_pszRegistryKey);

 m_pszRegistryKey = _tcsdup(lpszRegistryKey);

 free((void*)m_pszProfileName);

 m_pszProfileName = _tcsdup(m_pszAppName);

 AfxEnableMemoryTracking(bEnable);

}

void CWinApp::SetRegistryKey(UINT nIDRegistryKey)

{

 ASSERT(m_pszRegistryKey == NULL);

 TCHAR szRegistryKey[256];

 VERIFY(AfxLoadString(nIDRegistryKey, szRegistryKey));

 SetRegistryKey(szRegistryKey);

}

// returns key for HKEY_CURRENT_USER/"Software"/RegistryKey/ProfileName

// creating it if it doesn't exist

// responsibility of the caller to call RegCloseKey() on the returned HKEY

HKEY CWinApp::GetAppRegistryKey()

{

 ASSERT(m_pszRegistryKey != NULL);

 ASSERT(m_pszProfileName != NULL);

 HKEY hAppKey = NULL;

 HKEY hSoftKey = NULL;

 HKEY hCompanyKey = NULL;

 if (RegOpenKeyEx(HKEY_CURRENT_USER, _T("software"), 0, KEY_WRITE|KEY_READ,

  &hSoftKey) == ERROR_SUCCESS)

 {

  DWORD dw;

  if (RegCreateKeyEx(hSoftKey, m_pszRegistryKey, 0, REG_NONE,

   REG_OPTION_NON_VOLATILE, KEY_WRITE|KEY_READ, NULL,

   &hCompanyKey, &dw) == ERROR_SUCCESS)

  {

   RegCreateKeyEx(hCompanyKey, m_pszProfileName, 0, REG_NONE,

    REG_OPTION_NON_VOLATILE, KEY_WRITE|KEY_READ, NULL,

    &hAppKey, &dw);

  }

 }

 if (hSoftKey != NULL)

  RegCloseKey(hSoftKey);

 if (hCompanyKey != NULL)

  RegCloseKey(hCompanyKey);

 return hAppKey;

}

// returns key for:

//      HKEY_CURRENT_USER/"Software"/RegistryKey/AppName/lpszSection

// creating it if it doesn't exist.

// responsibility of the caller to call RegCloseKey() on the returned HKEY

HKEY CWinApp::GetSectionKey(LPCTSTR lpszSection)

{

 ASSERT(lpszSection != NULL);

 HKEY hSectionKey = NULL;

 HKEY hAppKey = GetAppRegistryKey();

 if (hAppKey == NULL)

  return NULL;

 DWORD dw;

 RegCreateKeyEx(hAppKey, lpszSection, 0, REG_NONE,

  REG_OPTION_NON_VOLATILE, KEY_WRITE|KEY_READ, NULL,

  &hSectionKey, &dw);

 RegCloseKey(hAppKey);

 return hSectionKey;

}

UINT CWinApp::GetProfileInt(LPCTSTR lpszSection, LPCTSTR lpszEntry,

 int nDefault)

{

 ASSERT(lpszSection != NULL);

 ASSERT(lpszEntry != NULL);

 if (m_pszRegistryKey != NULL) // use registry

 {

  HKEY hSecKey = GetSectionKey(lpszSection);

  if (hSecKey == NULL)

   return nDefault;

  DWORD dwValue;

  DWORD dwType;

  DWORD dwCount = sizeof(DWORD);

  LONG lResult = RegQueryValueEx(hSecKey, (LPTSTR)lpszEntry, NULL, &dwType,

   (LPBYTE)&dwValue, &dwCount);

  RegCloseKey(hSecKey);

  if (lResult == ERROR_SUCCESS)

  {

   ASSERT(dwType == REG_DWORD);

   ASSERT(dwCount == sizeof(dwValue));

   return (UINT)dwValue;

  }

  return nDefault;

 }

 else

 {

  ASSERT(m_pszProfileName != NULL);

  return ::GetPrivateProfileInt(lpszSection, lpszEntry, nDefault,

   m_pszProfileName);

 }

}

CString CWinApp::GetProfileString(LPCTSTR lpszSection, LPCTSTR lpszEntry,

 LPCTSTR lpszDefault)

{

 ASSERT(lpszSection != NULL);

 ASSERT(lpszEntry != NULL);

 if (m_pszRegistryKey != NULL)

 {

  HKEY hSecKey = GetSectionKey(lpszSection);

  if (hSecKey == NULL)

   return lpszDefault;

  CString strValue;

  DWORD dwType, dwCount;

  LONG lResult = RegQueryValueEx(hSecKey, (LPTSTR)lpszEntry, NULL, &dwType,

   NULL, &dwCount);

  if (lResult == ERROR_SUCCESS)

  {

   ASSERT(dwType == REG_SZ);

   lResult = RegQueryValueEx(hSecKey, (LPTSTR)lpszEntry, NULL, &dwType,

    (LPBYTE)strValue.GetBuffer(dwCount/sizeof(TCHAR)), &dwCount);

   strValue.ReleaseBuffer();

  }

  RegCloseKey(hSecKey);

  if (lResult == ERROR_SUCCESS)

  {

   ASSERT(dwType == REG_SZ);

   return strValue;

  }

  return lpszDefault;

 }

 else

 {

  ASSERT(m_pszProfileName != NULL);

  if (lpszDefault == NULL)

   lpszDefault = _T(""); // don't pass in NULL

  TCHAR szT[4096];

  DWORD dw = ::GetPrivateProfileString(lpszSection, lpszEntry,

   lpszDefault, szT, _countof(szT), m_pszProfileName);

  ASSERT(dw < 4095);

  return szT;

 }

}

BOOL CWinApp::GetProfileBinary(LPCTSTR lpszSection, LPCTSTR lpszEntry,

 BYTE** ppData, UINT* pBytes)

{

 ASSERT(lpszSection != NULL);

 ASSERT(lpszEntry != NULL);

 ASSERT(ppData != NULL);

 ASSERT(pBytes != NULL);

 *ppData = NULL;

 *pBytes = 0;

 if (m_pszRegistryKey != NULL)

 {

  HKEY hSecKey = GetSectionKey(lpszSection);

  if (hSecKey == NULL)

   return FALSE;

  DWORD dwType, dwCount;

  LONG lResult = RegQueryValueEx(hSecKey, (LPTSTR)lpszEntry, NULL, &dwType,

   NULL, &dwCount);

  *pBytes = dwCount;

  if (lResult == ERROR_SUCCESS)

  {

   ASSERT(dwType == REG_BINARY);

   *ppData = new BYTE[*pBytes];

   lResult = RegQueryValueEx(hSecKey, (LPTSTR)lpszEntry, NULL, &dwType,

    *ppData, &dwCount);

  }

  RegCloseKey(hSecKey);

  if (lResult == ERROR_SUCCESS)

  {

   ASSERT(dwType == REG_BINARY);

   return TRUE;

  }

  else

  {

   delete [] *ppData;

   *ppData = NULL;

  }

  return FALSE;

 }

 else

 {

  ASSERT(m_pszProfileName != NULL);

  CString str = GetProfileString(lpszSection, lpszEntry, NULL);

  if (str.IsEmpty())

   return FALSE;

  ASSERT(str.GetLength()%2 == 0);

  INT_PTR nLen = str.GetLength();

  *pBytes = UINT(nLen)/2;

  *ppData = new BYTE[*pBytes];

  for (int i=0;i<nLen;i+=2)

  {

   (*ppData)[i/2] = (BYTE)

    (((str[i+1] - 'A') << 4) + (str[i] - 'A'));

  }

  return TRUE;

 }

}

#ifdef AFX_CORE3_SEG

#pragma code_seg(AFX_CORE3_SEG)

#endif

BOOL CWinApp::WriteProfileInt(LPCTSTR lpszSection, LPCTSTR lpszEntry,

 int nValue)

{

 ASSERT(lpszSection != NULL);

 ASSERT(lpszEntry != NULL);

 if (m_pszRegistryKey != NULL)

 {

  HKEY hSecKey = GetSectionKey(lpszSection);

  if (hSecKey == NULL)

   return FALSE;

  LONG lResult = RegSetValueEx(hSecKey, lpszEntry, NULL, REG_DWORD,

   (LPBYTE)&nValue, sizeof(nValue));

  RegCloseKey(hSecKey);

  return lResult == ERROR_SUCCESS;

 }

 else

 {

  ASSERT(m_pszProfileName != NULL);

  TCHAR szT[16];

  wsprintf(szT, _T("%d"), nValue);

  return ::WritePrivateProfileString(lpszSection, lpszEntry, szT,

   m_pszProfileName);

 }

}

BOOL CWinApp::WriteProfileString(LPCTSTR lpszSection, LPCTSTR lpszEntry,

   LPCTSTR lpszValue)

{

 ASSERT(lpszSection != NULL);

 if (m_pszRegistryKey != NULL)

 {

  LONG lResult;

  if (lpszEntry == NULL) //delete whole section

  {

   HKEY hAppKey = GetAppRegistryKey();

   if (hAppKey == NULL)

    return FALSE;

   lResult = ::RegDeleteKey(hAppKey, lpszSection);

   RegCloseKey(hAppKey);

  }

  else if (lpszValue == NULL)

  {

   HKEY hSecKey = GetSectionKey(lpszSection);

   if (hSecKey == NULL)

    return FALSE;

   // necessary to cast away const below

   lResult = ::RegDeleteValue(hSecKey, (LPTSTR)lpszEntry);

   RegCloseKey(hSecKey);

  }

  else

  {

   HKEY hSecKey = GetSectionKey(lpszSection);

   if (hSecKey == NULL)

    return FALSE;

   lResult = RegSetValueEx(hSecKey, lpszEntry, NULL, REG_SZ,

    (LPBYTE)lpszValue, (lstrlen(lpszValue)+1)*sizeof(TCHAR));

   RegCloseKey(hSecKey);

  }

  return lResult == ERROR_SUCCESS;

 }

 else

 {

  ASSERT(m_pszProfileName != NULL);

  ASSERT(lstrlen(m_pszProfileName) < 4095); // can't read in bigger

  return ::WritePrivateProfileString(lpszSection, lpszEntry, lpszValue,

   m_pszProfileName);

 }

}

BOOL CWinApp::WriteProfileBinary(LPCTSTR lpszSection, LPCTSTR lpszEntry,

 LPBYTE pData, UINT nBytes)

{

 ASSERT(lpszSection != NULL);

 if (m_pszRegistryKey != NULL)

 {

  LONG lResult;

  HKEY hSecKey = GetSectionKey(lpszSection);

  if (hSecKey == NULL)

   return FALSE;

  lResult = RegSetValueEx(hSecKey, lpszEntry, NULL, REG_BINARY,

   pData, nBytes);

  RegCloseKey(hSecKey);

  return lResult == ERROR_SUCCESS;

 }

 // convert to string and write out

 LPTSTR lpsz = new TCHAR[nBytes*2+1];

 UINT i;

 for (i = 0; i < nBytes; i++)

 {

  lpsz[i*2] = (TCHAR)((pData[i] & 0x0F) + 'A'); //low nibble

  lpsz[i*2+1] = (TCHAR)(((pData[i] >> 4) & 0x0F) + 'A'); //high nibble

 }

 lpsz[i*2] = 0;

 ASSERT(m_pszProfileName != NULL);

 BOOL bResult = WriteProfileString(lpszSection, lpszEntry, lpsz);

 delete[] lpsz;

 return bResult;