How to read a value from the Windows registry

Question

Given the key for some registry value (e.g. HKEY_LOCAL_MACHINE\blah\blah\blah\foo) how can I:

1. Safely determine that such a key exists.
2. Programmatically (i.e. with code) get its value.

I have absolutely no intention of writing anything back to the registry (for the duration of my career if I can help it). So we can skip the lecture about every molecule in my body exploding at the speed of light if I write to the registry incorrectly.

Prefer answers in C++, but mostly just need to know what the special Windows API incantation to get at the value is.

Answer 1

Here is some pseudo-code to retrieve the following:

1. If a registry key exists
2. What the default value is for that registry key
3. What a string value is
4. What a DWORD value is

Example code:

Include the library dependency: Advapi32.lib

HKEY hKey; LONG lRes = RegOpenKeyExW(HKEY_LOCAL_MACHINE, L"SOFTWARE\\Perl", 0, KEY_READ, &hKey); bool bExistsAndSuccess (lRes == ERROR_SUCCESS); bool bDoesNotExistsSpecifically (lRes == ERROR_FILE_NOT_FOUND); std::wstring strValueOfBinDir; std::wstring strKeyDefaultValue; GetStringRegKey(hKey, L"BinDir", strValueOfBinDir, L"bad"); GetStringRegKey(hKey, L"", strKeyDefaultValue, L"bad");  LONG GetDWORDRegKey(HKEY hKey, const std::wstring &strValueName, DWORD &nValue, DWORD nDefaultValue) {     nValue = nDefaultValue;     DWORD dwBufferSize(sizeof(DWORD));     DWORD nResult(0);     LONG nError = ::RegQueryValueExW(hKey,         strValueName.c_str(),         0,         NULL,         reinterpret_cast<LPBYTE>(&nResult),         &dwBufferSize);     if (ERROR_SUCCESS == nError)     {         nValue = nResult;     }     return nError; }   LONG GetBoolRegKey(HKEY hKey, const std::wstring &strValueName, bool &bValue, bool bDefaultValue) {     DWORD nDefValue((bDefaultValue) ? 1 : 0);     DWORD nResult(nDefValue);     LONG nError = GetDWORDRegKey(hKey, strValueName.c_str(), nResult, nDefValue);     if (ERROR_SUCCESS == nError)     {         bValue = (nResult != 0) ? true : false;     }     return nError; }   LONG GetStringRegKey(HKEY hKey, const std::wstring &strValueName, std::wstring &strValue, const std::wstring &strDefaultValue) {     strValue = strDefaultValue;     WCHAR szBuffer[512];     DWORD dwBufferSize = sizeof(szBuffer);     ULONG nError;     nError = RegQueryValueExW(hKey, strValueName.c_str(), 0, NULL, (LPBYTE)szBuffer, &dwBufferSize);     if (ERROR_SUCCESS == nError)     {         strValue = szBuffer;     }     return nError; }