Writing/Reading string in Registry in C++

Question

How to write/read a string in windows registry in C++ ?

I am able to write/read DWORD (number) in windows registry using the following code. But, unable to write/read a string value, as it gets stored as chinese like characters in the registry.

void SetVal(HKEY hKey, LPCTSTR lpValue, DWORD data)
{
    LONG nError = RegSetValueEx(hKey, lpValue, NULL, REG_DWORD, (LPBYTE)&data, sizeof(DWORD));

    if (nError)
        cout << "Error: " << nError << " Could not set registry value: " << (char*)lpValue << endl;
}

DWORD GetVal(HKEY hKey, LPCTSTR lpValue)
{
    DWORD data;     DWORD size = sizeof(data);  DWORD type = REG_DWORD;
    LONG nError = RegQueryValueEx(hKey, lpValue, NULL, &type, (LPBYTE)&data, &size);

    if (nError==ERROR_FILE_NOT_FOUND)
        data = 0; // The value will be created and set to data next time SetVal() is called.
    else if (nError)
        cout << "Error: " << nError << " Could not get registry value " << (char*)lpValue << endl;

    return data;
}

Code used to write/read string value (Stored as chinese like characters in the registry):

void SetVal(HKEY hKey, LPCTSTR lpValue, string data)
{
    LONG nError = RegSetValueEx(hKey, lpValue, NULL, REG_SZ, (LPBYTE)&data, sizeof(data));

    if (nError)
        cout << "Error: " << nError << " Could not set registry value: " << (char*)lpValue << endl;
}

string GetVal(HKEY hKey, LPCTSTR lpValue)
{
    string data;     DWORD size = sizeof(data);  DWORD type = REG_SZ;
    LONG nError = RegQueryValueEx(hKey, lpValue, NULL, &type, (LPBYTE)&data, &size);

    if (nError==ERROR_FILE_NOT_FOUND)
        data = "0"; // The value will be created and set to data next time SetVal() is called.
    else if (nError)
        cout << "Error: " << nError << " Could not get registry value " << (char*)lpValue << endl;

    return data;
}

Answer 1

The problem with your code is that you are naively casting string type variables to LPBYTE .

This is your code with corrections:

void SetVal(HKEY hKey, LPCTSTR lpValue, string data)
{
  const char *x = data.c_str();
  LONG nError = RegSetValueEx(hKey, lpValue, NULL, REG_SZ, (LPBYTE)data.c_str(), data.size());

  if (nError)
    cout << "Error: " << nError << " Could not set registry value: " << (char*)lpValue << endl;
}

string GetVal(HKEY hKey, LPCTSTR lpValue)
{
  string data; 
#define MAXLENGTH 100

  char buffer[100];
  DWORD size = sizeof(buffer);
  DWORD type = REG_SZ;

  LONG nError = RegQueryValueEx(hKey, lpValue, NULL, &type, (LPBYTE)buffer, &size);

  if (nError == ERROR_FILE_NOT_FOUND)
  {
    data = "0"; // The value will be created and set to data next time SetVal() is called.
    return data;
  }
  else if (nError)
    cout << "Error: " << nError << " Could not get registry value " << (char*)lpValue << endl;

  data = buffer;
  return data;
}

There is still room for improvement, for example the maximum string length is limited to 100 and the error handling should be improved.

Explanations:

This is your code in SetVal

RegSetValueEx(hKey, lpValue, NULL, REG_DWORD, (LPBYTE)&data, sizeof(DWORD));

• you are naively casting data to LPBYTE .
• sizeof(DWORD) is wrong, because you need to provide the length of the string

This is your code in GetVal :

    string data;
    DWORD size = sizeof(data);
    DWORD type = REG_SZ;
    LONG nError = RegQueryValueEx(hKey, lpValue, NULL, &type, (LPBYTE)&data, &size);

• sizeof(data) when data is a string doesn't make any sense. It is not the length of the string, which at that moment is 0 anyway.
• you are again casting naively string to LPBYTE when calling RegQueryValueEx