Show value name and data using RegEnumValue - c++

Question

I have the following code:
#include <Windows.h>
#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
using namespace std;
int main(int argc, wchar_t*argv[])
{
std::locale::global(std::locale("spanish"));
/*Declaración de variables*/
HKEY hKey = HKEY_CURRENT_USER;
LPCTSTR lpSubKey = TEXT("Software\\Microsoft\\Windows\\CurrentVersion\\Explorer\\RunMRU");
DWORD ulOptions = 0;
REGSAM samDesired = KEY_READ | KEY_WRITE;
HKEY phkResult;
DWORD dwIndex = 0;
TCHAR lpValueName[16383];
DWORD lpcchValueName = 16383;
LPTSTR lpData="";
long OpenK = RegOpenKeyEx(hKey, lpSubKey, ulOptions, samDesired, &phkResult);
if (OpenK == ERROR_SUCCESS)
{
long R = RegEnumValue(phkResult, dwIndex, lpValueName, &lpcchValueName, NULL, NULL,(LPBYTE)lpData, NULL);
if (R == ERROR_SUCCESS)
{
cout << "The value and data is: \n" << lpValueName << ": " << lpData << endl;
//printf(TEXT("(%d) %s\n"), lpValueName);
}
else
cout << "Error: " << R << endl;
}
else if (OpenK == ERROR_FILE_NOT_FOUND)
{
cout << "La sub-clave RunMRU no existe." << endl;
}
else if (OpenK == ERROR_ACCESS_DENIED)
{
cout << "Acceso denegado al abrir la sub-clave RunMRU." << endl;
}
else
{
cout << "Error al abrir la clave de registro. Código: " << OpenK << endl;
}
system("Pause");
}
I am trying to show both, the Value name, and its Data using the RegEnumValue in the first if (The value and data is:) but I can only show the Value name.
Is there any way to do that? I'm trying to figure out how to use the lpData, but I can't because I only receive error 87 (Incorrect parameters) or nothing (If I set NULL instead).

Answer 1

You're not providing a suitable buffer for RegEnumValue() to store the data.
LPTSTR lpData="";
This is just a string literal, of at most 2 bytes in size, and is almost certainly not writable anyway. You need to allocate an area of memory and pass that to RegEnumValue() to read the data back for each value.
Your first step should be to use RegQueryInfoKey() to find out how big the largest data value is. I showed you how to use this function in a previous answer to query the size of the largest value name - the process is the same. See the docs for RegQueryInfoKey() to find out which parameter provides the data size.
Once you know how big your largest item of data is, allocate a buffer for it:
void* pData = malloc(dwLargestValueSize);
// remember this buffer needs to be freed at the end with free()
You then pass that buffer, plus a value indicating its size, to RegEnumValue().
Something else you need to be aware of is that registry values can be different types - REG_DWORD, REG_SZ, etc, and the data you get back from RegEnumValue() is the raw data. RegEnumValue() can also return a value indicating the type of data and if you're to properly interpret it, you absolutely need to check this as well.

Answer 2

Changes to your code to get a string value into lpData:
#define MAX_DATA_LENGTH 16383
char* lpData = new char[MAX_DATA_LENGTH];
DWORD lpDataLength = MAX_DATA_LENGTH;
RegEnumValue(phkResult, dwIndex, lpValueName, &lpcchValueName, NULL, NULL, (unsigned char*)lpData, &lpDataLength);