Function ReadRegString

source/util.cpp:1901–1950

DWORD ReadRegString(HKEY aRootKey, LPTSTR aSubkey, LPTSTR aValueName, LPTSTR aBuf, DWORD aBufSize, DWORD aFlag)
// Returns the length of the string (0 if empty).
// Caller must ensure that size of aBuf is REALLY aBufSize (even when it knows aBufSize is more than
// it needs) because the API apparently reads/writes parts of the buffer beyond the string it writes!
// Caller must ensure that aBuf isn't NULL because it doesn't seem worth having a "give me the size only" mode.
// This is because the API might return a size that omits the zero terminator, and the only way to find out for
// sure is probably to actually fetch the data and check if the terminator is present.
{
	HKEY hkey;
	if (RegOpenKeyEx(aRootKey, aSubkey, 0, KEY_QUERY_VALUE | aFlag, &hkey) != ERROR_SUCCESS)
	{
		*aBuf = '\0';
		return 0;
	}
	DWORD buf_size = aBufSize * sizeof(TCHAR); // Caller's value might be a constant memory area, so need a modifiable copy.
	LONG result = RegQueryValueEx(hkey, aValueName, NULL, NULL, (LPBYTE)aBuf, &buf_size);
	RegCloseKey(hkey);
	if (result != ERROR_SUCCESS || !buf_size) // Relies on short-circuit boolean order.
	{
		*aBuf = '\0'; // MSDN says the contents of the buffer is undefined after the call in some cases, so reset it.
		return 0;
	}
	buf_size /= sizeof(TCHAR); // RegQueryValueEx returns size in bytes.
	// Otherwise success and non-empty result.  This also means that buf_size is accurate and <= to what we sent in.
	// Fix for v1.0.47: ENSURE PROPER STRING TERMINATION. This is suspected to be a source of crashing.
	// MSDN: "If the data has the REG_SZ, REG_MULTI_SZ or REG_EXPAND_SZ type, the string may not have been
	// stored with the proper null-terminating characters. Therefore, even if the function returns
	// ERROR_SUCCESS, the application should ensure that the string is properly terminated before using
	// it; otherwise, it may overwrite a buffer. (Note that REG_MULTI_SZ strings should have two
	// null-terminating characters.)"
	// MSDN: "If the data has the REG_SZ, REG_MULTI_SZ or REG_EXPAND_SZ type, this size includes any
	// terminating null character or characters."
	--buf_size; // Convert to the index of the last character written.  This is safe because above already checked that buf_size>0.
	if (aBuf[buf_size] == '\0') // It wrote at least one zero terminator (it might write more than one for Unicode, or if it's simply stored with more than one in the registry).
	{
		while (buf_size && !aBuf[buf_size - 1]) // Scan leftward in case more than one consecutive terminator.
			--buf_size;
		return buf_size; // There's a tiny chance that this could the wrong length, namely when the string contains binary zero(s) to the left of non-zero characters.  But that seems too rare to be worth calling strlen() for.
	}
	// Otherwise, it didn't write a terminator, so provide one.
	++buf_size; // To reflect the fact that we're about to write an extra char.
	if (buf_size >= aBufSize) // There's no room for a terminator without truncating the data (very rare).  Seems best to indicate failure.
	{
		*aBuf = '\0';
		return 0;
	}
	// Otherwise, there's room for the terminator.
	aBuf[buf_size] = '\0';
	return buf_size; // There's a tiny chance that this could the wrong length, namely when the string contains binary zero(s) to the left of non-zero characters.  But that seems too rare to be worth calling strlen() for.
}