Win 95及NT的注册数据库(Registry)是系统中非常重要的组成部分。在Win32 API中有一组Reg函数来处理这些问题。其一般的读写过程如下：
 
    1、使用RegOpenKeyEx或RegCreateKeyEx函数打开或创建一个键；
    2、如果上一步成功，使用RegQueryValueEx读取子键的值，使用RegSetValueEx设置子键值，使用RegEnumKey获得所有子键，使用RegDeleteKey删除一个键；
    3、完成操作后使用RegCloseKey关闭键。
    下面这段程序打开HKEY_CURRENT_USER\Software\Zeal SoftStudio\AskPro FTP\LastTime键，然后读取WOL子键的值。

    HKEY hkey;
    char sz[256];
    DWORD dwtype, sl = 256;
    
    RegOpenKeyEx(HKEY_CURRENT_USER,
    "Software\\Zeal SoftStudio\\AskPro FTP\\LastTime",
    NULL, KEY_ALL_ACCESS, &hkey);
    RegQueryValueEx(hkey, "WOL", NULL, &dwtype, (LPBYTE)sz, &sl);
    RegCloseKey(hkey);
    MFC程序可以使用CRegKey类读写注册表。VB中调用API的办法可以参考QA000226 "如何访问Windows系统注册表"。

    打开注册键
    LONG RegOpenKeyEx( HKEY hKey,  // handle to open key

    LPCTSTR lpSubKey,              // address of name of subkey to open
    DWORD ulOptions,               // reserved =0
    REGSAM samDesired,             // security access mask
    PHKEY phkResult                // address of handle to open key
    );

    例:
    HKEY hd;
    hd=HKEY_LOCAL_MACHINE;
    char* Regkeyname="SoftWare\\Xy123\\Poker\\";
    LONG a=RegOpenKeyEx(hd,Regkeyname,0,KEY_READ,&hd);   //成功返回ERROR_SUCCESS,否则返回错误代码
 

    关闭注册键
    LONG RegCloseKey( HKEY hKey // handle to key to close );
例:
     RegCloseKey(HKEY_LOCAL_MACHINE);
OR:  RegCloseKey(hd);
建立注册键
LONG RegCreateKeyEx( HKEY hKey, // handle to an open key
      LPCTSTR lpSubKey, // address of subkey name
      DWORD Reserved, // reserved =0
      LPTSTR lpClass, // address of class string
      DWORD dwOptions, // special options flag
      REGSAM samDesired, // desired security access

      LPSECURITY_ATTRIBUTES lpSecurityAttributes, // address of key security         structure
      PHKEY phkResult, // address of buffer for opened handle
      LPDWORD lpdwDisposition // address of disposition value buffer );
例:
   char *sclass="";  //类名指定为空
   DWORD nbf=0;    //接受返回值,指明是建立新键还是打开已有的键.(经试验总是返回REG_OPENED_EXISTING_KEY.
   LONG II=RegCreateKeyEx(hd,Regkeyname,0,sclass,REG_OPTION_NON_VOLATILE,
                KEY_READ|KEY_WRITE,NULL,&hd,&nbf);

//REG_OPTION_NON_VOLATILE 指明键永久保留.安全结构指明NULL,自动获得一默认值
//成功返回ERROR_SUCCESS,否则返回错误代码
枚举键值
LONG RegEnumValue( HKEY hKey, // handle to key to query
      DWORD dwIndex, // index of value to query
      LPTSTR lpValueName, // address of buffer for value string
      LPDWORD lpcbValueName, // address for size of value buffer
      LPDWORD lpReserved, // reserved =NULL
      LPDWORD lpType, // address of buffer for type code

      LPBYTE lpData, // address of buffer for value data
      LPDWORD lpcbData // address for size of data buffer);
例:
   DWORD dinx=0;
   char valuename[70];  //分配数值名称缓冲区
   strcpy(valuename,"DeskPattern");  //随便指定哪个键值名
   DWORD nsize=69;  //数值名称缓冲区大小
   DWORD k=REG_SZ;  //指明数据类型
   unsigned char vari[70]; //分配数值缓冲区
   DWORD ncbvari=69; //数值缓冲区大小
   dinx=0; //从0开始

   while((II=RegEnumValue(hd,dinx,valuename,&nsize,NULL,&k,vari,&ncbvari))
          != ERROR_NO_MORE_ITEMS)
   {
       dinx++;//索引 +1,准备取下一个值
       nsize=69; //恢复原来大小
       ncbvari=69;
   }
成功后返回值0,各变量返回后设置如下:
valuename=数值名称,以0结尾;如 : DeskColor
nsize=数值名称长度, 9
k=REG_SZ  DeskColor 的类型为 REG_SZ
vari=键值,32768 DeskColor="32768",
ncbvari=键值长度 REG_SZ包括结尾0,=6,
读取键值
LONG RegQueryValueEx( HKEY hKey, // handle to key to query

       LPTSTR lpValueName, // address of name of value to query
       LPDWORD lpReserved, // reserved
       LPDWORD lpType, // address of buffer for value type
       LPBYTE lpData, // address of data buffer
       LPDWORD lpcbData // address of data buffer size );
例:
   RegQueryValueEx(hd,valuename,NULL,&k,vari,&ncbvari);
变量定义及成功后各变量设置值同RegEnumValueEx
写键值
LONG RegSetValueEx( HKEY hKey, // handle to key to set value for
       LPCTSTR lpValueName, // name of the value to set

       DWORD Reserved, // reserved
       DWORD dwType, // flag for value type
       CONST BYTE *lpData, // address of value data
       DWORD cbData // size of value data );
例:
   strcpy(valuename,"Hello");
   unsigned char vari[10];
   DWORD k=REG_SZ;
   strcpy((char*)vari,"1234567")
   RegSetValueEx(hd,valuename,0,k,vari,7);
成功后在Poker下增加一个键值 Hello : REG_SZ : 1234567
写整型变量：
int hi=8;
RegSetValueEx(pj,valuename,0,REG_BINARY,(unsigned char*)&hi,sizeof(int));

成功后在Poker下增加一个键值 Hello2 : REG_BINARY :08 00 00 00

void AddEventSource()
{
    HKEY hk;
    DWORD dwData;
    UCHAR szBuf[80];

    // Add your source name as a subkey under the Application
    // key in the EventLog registry key.

    if (RegCreateKey(HKEY_LOCAL_MACHINE,
            "SYSTEM\\CurrentControlSet\\Services\
            \\EventLog\\Application\\SamplApp", &hk))
        ErrorExit("Could not create the registry key.");

    // Set the name of the message file.

    strcpy(szBuf, "%SystemRoot%\\System\\SamplApp.dll");

    // Add the name to the EventMessageFile subkey.

    if (RegSetValueEx(hk,             // subkey handle
            "EventMessageFile",       // value name
            0,                        // must be zero
            REG_EXPAND_SZ,            // value type
            (LPBYTE) szBuf,           // pointer to value data
            strlen(szBuf) + 1))       // length of value data

        ErrorExit("Could not set the event message file.");

    // Set the supported event types in the TypesSupported subkey.

    dwData = EVENTLOG_ERROR_TYPE | EVENTLOG_WARNING_TYPE |
        EVENTLOG_INFORMATION_TYPE;

    if (RegSetValueEx(hk,      // subkey handle
            "TypesSupported",  // value name
            0,                 // must be zero
            REG_DWORD,         // value type
            (LPBYTE) &dwData,  // pointer to value data

            sizeof(DWORD)))    // length of value data
        ErrorExit("Could not set the supported types.");

    RegCloseKey(hk);
}

以下代码把注册表自启动shell的键值改写为C:\DK1\ATM\HARP\ExAtmShell.exe:

         HKEY hkey;
LONG res;
DWORD datatype=REG_SZ;
unsigned char szvalue[_MAX_PATH];
strcpy((char*)szvalue,"C:\\DK1\\ATM\\HARP\\ExAtmShell.exe");

res =::RegOpenKeyEx(HKEY_LOCAL_MACHINE,
"SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion\\Winlogon\\", 0,
KEY_WRITE|KEY_READ, &hkey);

if(res!=ERROR_SUCCESS)
{
AfxMessageBox("aaa");
return;
}
res = ::RegSetValueEx(hkey, "Shell", 0, datatype, szvalue, strlen(LPCSTR(szvalue)));

RegCloseKey(hkey);
if(res==ERROR_SUCCESS)
::AfxMessageBox("你已经成功地将注册表自启动shell的键值设置为C:\\DK1\\ATM\\HARP\\ExAtmShell.exe");
else
::AfxMessageBox("设定失败:目标位置不存在这样的键!");