Cannot read string from Windows registry

Question

My goal is to get the current SetupPath of the installed Outlook Version.

I use the following code in order to achieve that:

HKEY hKey;

LONG lReturn = RegOpenKeyEx(HKEY_LOCAL_MACHINE,
    _T("SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\App Paths\\OUTLOOK.EXE"),
    0L,
    KEY_ALL_ACCESS,
    &hKey);

if (lReturn == ERROR_SUCCESS)
{
    CString strData;
    DWORD   dwSize = 1024;
    DWORD   dwType;

    lReturn = RegQueryValueEx(hKey,
        _T("Path"),
        0L,
        &dwType,
        (BYTE *)strData.GetBufferSetLength((int)dwSize),
        &dwSize);

    if (lReturn == ERROR_SUCCESS)
    {
        cout << strData;
    }
    else {
        cout << "Read DWORD failed";
    }
}
else {
    cout << "Open Key failed";
}

RegCloseKey(hKey);

But however this won't work. It fails at opening the Key.

EDIT

I found that the "open key failed" Output was simply an Acces Denied caused by non admin rights. But however if i run it in Admin mode the output is a Hexadecimal Value which will change everytime.

Answer 1

First, since you are using C++, consider making your coding life simpler, defining a simple class that automatically calls RegCloseKey() on the open key.

Then, when you open the key, consider the minimum flag you need for access: in particular, this sounds like KEY_READ in your case.

Moreover, I would call RegGetValue() instead of RegQueryValueEx(), as the former makes sure that the returned string is NUL-terminated (simplifying your code a little bit).

Moreover, when you print the CString, consider calling its GetString() method, to get the const wchar_t* C-style string pointer, instead of passing the CString object to cout.

Finally, I've simplified your code using wchar_t instead of TCHAR.

Compilable code follows (I used VS2015 and tested it on Windows 10):

#include <Windows.h>
#include <atlbase.h>
#include <atlstr.h>
#include <iostream>
using namespace std;

class ScopedKey
{
public:
    explicit ScopedKey(HKEY hKey)
        : m_hKey(hKey)
    {
    }

    ~ScopedKey()
    {
        ::RegCloseKey(m_hKey);
    }

    HKEY Get() const
    {
        return m_hKey;
    }

    // Ban copy
    ScopedKey(const ScopedKey&) = delete;
    ScopedKey& operator=(const ScopedKey&) = delete;

private:
    HKEY m_hKey;
};

int main()
{
    constexpr int kExitOk = 0;
    constexpr int kExitError = 1;

    //
    // Open the registry key
    // 
    HKEY hKey;
    LONG retCode = ::RegOpenKeyEx(
        HKEY_LOCAL_MACHINE,
        L"SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\App Paths\\OUTLOOK.EXE",
        0,
        KEY_READ,
        &hKey
    );

    if (retCode != ERROR_SUCCESS)
    {
        wcout << "RegOpenKeyEx() failed; error code = " << retCode << '\n';
        return kExitError;
    }

    // Auto-close the registry key
    ScopedKey key(hKey);


    //
    // Get the size of the path string
    //
    const wchar_t* valueName = L"Path";
    DWORD dataSizeInBytes = 0;
    retCode = ::RegGetValue(
        hKey, 
        nullptr, 
        valueName, 
        RRF_RT_REG_SZ, 
        nullptr, 
        nullptr, 
        &dataSizeInBytes
    );
    if (retCode != ERROR_SUCCESS)
    {
        wcout << "RegGetValue() failed; error code = " << retCode << '\n';
        return kExitError;
    }


    //
    // Read the path string from the registry
    // 
    const DWORD sizeInWchars = dataSizeInBytes / sizeof(wchar_t);
    CStringW str;
    wchar_t* buffer = str.GetBuffer(sizeInWchars);
    retCode = ::RegGetValue(
        hKey,
        nullptr,
        valueName,
        RRF_RT_REG_SZ,
        nullptr,
        buffer,
        &dataSizeInBytes
    );
    if (retCode != ERROR_SUCCESS)
    {
        wcout << "RegGetValue() failed; error code = " << retCode << '\n';
        return kExitError;
    }
    str.ReleaseBuffer();

    wcout << L"Path = [" << str.GetString() << L"]\n";

    // Auto-closed at end of scope
    // ::RegCloseKey(hKey);

    return kExitOk;
}

Output:

Path = [C:\Program Files (x86)\Microsoft Office\Root\Office16\]

---

In addition, you can even use RegGetValue() to automatically open (and close) the registry key for you, e.g.:

#include <Windows.h>
#include <atlbase.h>
#include <atlstr.h>
#include <iostream>
using namespace std;

int main()
{
    constexpr int kExitOk = 0;
    constexpr int kExitError = 1;

    //
    // Get the size of the path string
    //
    const wchar_t* subKey = L"SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\App Paths\\OUTLOOK.EXE";
    const wchar_t* valueName = L"Path";
    DWORD dataSizeInBytes = 0;
    LONG retCode = ::RegGetValue(
        HKEY_LOCAL_MACHINE,
        subKey,
        valueName,
        RRF_RT_REG_SZ,
        nullptr,
        nullptr,
        &dataSizeInBytes
    );
    if (retCode != ERROR_SUCCESS)
    {
        wcout << "RegGetValue() failed; error code = " << retCode << '\n';
        return kExitError;
    }

    //
    // Read the path string from the registry
    // 
    const DWORD sizeInWchars = dataSizeInBytes / sizeof(wchar_t);
    CStringW str;
    wchar_t* buffer = str.GetBuffer(sizeInWchars);
    retCode = ::RegGetValue(
        HKEY_LOCAL_MACHINE,
        subKey,
        valueName,
        RRF_RT_REG_SZ,
        nullptr,
        buffer,
        &dataSizeInBytes
    );
    if (retCode != ERROR_SUCCESS)
    {
        wcout << "RegGetValue() failed; error code = " << retCode << '\n';
        return kExitError;
    }
    str.ReleaseBuffer();

    wcout << L"Path = [" << str.GetString() << L"]\n";

    return kExitOk;
}