ExpandEnvironmentStrings - Changing Environment Variables

// Changing Environment Variables
int _ExpandEnvironmentStrings( LPTSTR pText )
{
    TCHAR* p1 = _tcschr( pText, _T('%') );
    if( p1 == NULL )
        return -1;

    TCHAR* p2 = _tcschr( p1 +1, _T('%') );
    if( p2 == NULL )
        return -1;

    TCHAR provi[MAX_PATH +1];
    provi[0] = TCHAR(0);
    TCHAR env[MAX_PATH +1];
    p1 = pText;
    TCHAR* d = provi;
    while( *p1 != TCHAR(0) )
    {
        if( *p1 != _T('%') )
        {
            *d++ = *p1++;
            continue;
        }

        // find %
        p2 = _tcschr( p1 +1, _T('%') );
        if( p2 == NULL )
            return -1;

        lstrcpyn( env, p1 +1, int(p2 - p1) );
        TCHAR newEnv[MAX_PATH +1];
        DWORD res = ::GetEnvironmentVariable( env, newEnv, MAX_PATH );
        if( res > 0 )
        {
            lstrcpy( d, newEnv );
            d += lstrlen( newEnv );
        }
        p1 = p2 +1;
    }
    *d = TCHAR(0);

    if( lstrlen( provi ) != 0 )
    {
        lstrcpy( pText, provi );
    }

    return 0;
}