WinReg v10.0.0

High-level C++ Wrapper Around the Low-level Windows Registry C-interface API

by Giovanni Dicanio

The Windows Registry C-interface API is very low-level and hard to use.

I developed some C++ wrappers around this low-level Win32 API, to raise the semantic level, using C++ classes like std::wstring, std::vector, etc. instead of raw C-style buffers and low-level mechanisms.

For example, the REG_MULTI_SZ registry type associated to double-NUL-terminated C-style strings is handled using a much easier higher-level vector<wstring>. My C++ code does the translation between high-level C++ STL-based stuff and the low-level Win32 C-interface API.

Moreover, Win32 error codes are translated to C++ exceptions. However, note that if you prefer checking return codes, there are also methods that follow this pattern (e.g. TryXxxx() methods like TryOpen(), TryGetDwordValue(), TryGetStringValue(), etc.).

The Win32 registry value types are mapped to C++ higher-level types according the following table:

Win32 Registry Type	C++ Type
REG_DWORD	DWORD
REG_QWORD	ULONGLONG
REG_SZ	std::wstring
REG_EXPAND_SZ	std::wstring
REG_MULTI_SZ	std::vector<std::wstring>
REG_BINARY	std::vector<BYTE>, std::span<const BYTE> (input-only)

This code is currently developed using Visual Studio 2022 with C++20 features enabled (/std:c++20). I have no longer tested the code with previous compilers. The code compiles cleanly at warning level 4 (/W4) in 64-bit builds.

This is a header-only C++ library (clients should include the main public header WinReg/WinReg.hpp).

If you use Visual Studio, you can configure the IDE to find the library headers using the standard way:

Solution Explorer → right-click the project → Properties → Configuration Properties → C/C++ → General → Additional Include Directories.

Then click the drop-down next to Additional Include Directories → Edit...

and add the path, for example: $(SolutionDir)WinReg\Include

(Note that there is no backslash after $(SolutionDir))

WinRegTest.cpp contains some demo/test code for the library: check it out for some sample usage.

The library exposes four main classes:

• RegKey: a tiny efficient wrapper around raw Win32 HKEY handles
• RegException: an exception class to signal error conditions
• RegResult: a tiny wrapper around Windows Registry API LSTATUS error codes, returned by some Try methods (like RegKey::TryOpen())
• RegExpected<T>: an object that contains a value of type T (e.g. a DWORD read from the registry) on success, or an instance of a RegResult-wrapped return code on error

There are many member functions inside the RegKey class, that wrap several parts of the native C-interface Windows Registry API, in a convenient higher-level C++ way.

For example, you can simply open a registry key and get registry values with C++ code like this:

RegKey  key{ HKEY_CURRENT_USER, L"SOFTWARE\\SomeKey" };

DWORD   dw = key.GetDwordValue (L"SomeDwordValue");
wstring s  = key.GetStringValue(L"SomeStringValue");

NOTE: If the specified registry key does not exist, a new one is created by the constructor. If you want open-existing-only behavior, consider using the Open() or TryOpen() methods.

You can also open a registry key using a two-step construction process:

RegKey key;
key.Open(HKEY_CURRENT_USER, L"SOFTWARE\\SomeKey");

The above code will throw an exception on error. If you prefer to check return codes, you can do that as well, using a TryXxxx() method, e.g.:

RegKey key;
RegResult result = key.TryOpen(HKEY_CURRENT_USER, L"SOFTWARE\\SomeKey");
if (! result)
{
    //
    // Open failed.
    //
    // You can invoke the RegResult::Code and RegResult::ErrorMessage methods
    // for further details.
    //
    ...
}

You can also enumerate all the values under a given key with simple C++ code like this:

auto values = key.EnumValues();

for (const auto & v : values)
{
    //
    // Process current value:
    //
    //   - v.first  (wstring) is the value name
    //   - v.second (DWORD)   is the value type
    //
    ...
}

You can simplify the above iteration code using structured bindings, as well:

auto values = key.EnumValues();

for (const auto & [valueName, valueType] : values)
{
    //
    // Use valueName and valueType
    //
    ...
}

You can also check if a key contains a given value or even a subkey, invoking the RegKey::ContainsValue() and RegKey::ContainsSubKey() methods, e.g.:

if (key.ContainsValue(L"Connie"))
{
    // The key contains the value named "Connie"
    ...
}

You can also use the RegKey::TryGet...Value() methods, that return RegExpected<T> instead of throwing an exception on error:

//
// RegKey::TryGetDwordValue() returns a RegExpected<DWORD>;
// the returned RegExpected contains a DWORD on success, 
// or a RegResult instance on error.
//
// 'res' is a RegExpected<DWORD> in this case:
//
const auto res = key.TryGetDwordValue(L"SomeDwordValue");
if (res.IsValid())  // or simply:  if (res)
{
    //
    // All right: Process the returned value ...
    //
    // Use res.GetValue() to access the stored DWORD.
    //
}
else
{
    //
    // The method has failed: 
    //
    // The returned RegExpected contains a RegResult with an error code.
    // Use res.GetError() to access the RegResult object.
    //
}

The library also supports reading raw binary data for Registry types that are unsupported or less documented (e.g. REG_RESOURCE_LIST, REG_FULL_RESOURCE_DESCRIPTOR, etc.), via the RegKey::GetRawValue() and RegKey::TryGetRawValue() methods.

Version Note: WinReg v5.1.1 is the latest version in which the TryGetXxxValue() methods return std::optional<T> (discarding the information about the error code). Starting from v6.0.0, the TryGetXxxxValue() methods return RegExpected<T> (which keeps the error information on failure).

Note that many methods are available in two forms: one that throws an exception of type RegException on error (e.g. RegKey::Open()), and another that returns an error status object of type RegResult (e.g. RegKey::TryOpen()) instead of throwing an exception. In addition, as indicated above, some methods like the RegKey::TryGet...Value() ones return RegExpected instead of throwing exceptions; in case of errors, the returned RegExpected contains a RegResult storing the error code.

You can take a look at the test code in WinRegTest.cpp for some sample usage.

The library stuff lives under the winreg namespace.

Thanks to everyone who contributed to this project with some additional features and constructive comments and suggestions.

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Improvements in v10.0.0

• Fixed wrong positions of [[nodiscard]] in some places (see e.g. https://giodicanio.com/2026/10/12/where-to-put-nodiscard-a-silent-trap-with-msvc/).
• Furtherly simplified comparison code using new C++20 features.
• Fixed ConnectRegistry() and TryConnectRegistry(), invoking Close() only after the connection is successfully opened.
• RegTypeToString() now returns a const wchar_t* instead of creating new wstring objects every time it's invoked (with potential dynamic memory allocations). Moreover, the list of recognized registry types has been extended.
• SetQwordValue() and TrySetQwordValue() now get the ULONGLONG data parameter by value instead of const&.
• Get rid of the trailing '\r\n' returned by FormatMessage() in RegResult::ErrorMessage().
• Add _ASSERTE(IsValid()) in places like QueryReflectionKey() and similar reflection methods where it was missing.
• Added a safety check in ScopedLocalFree::AddressOf() to free any allocated memory before returning write access to the pointer member.
• Simplified the InfoKey structure code using member initialization.
• Simplified code using C++20's std::in_range() instead of custom code in SafeCast.hpp.
• Improved parsing behavior of double-NUL-terminated strings, including some edge cases.
• Improved RegKey's methods ContainsSubKey() and TryContainsSubKey().

Improvements in v8.0.0

• Moved the codebase to C++20 (this is the first release targeting C++20).
• Added std::span<const BYTE> overloads for some RegKey methods, like SetBinaryValue() and TrySetBinaryValue().
• Used "spaceship operator" for comparing RegKey objects instead of previous "classic" relational operator overloads.