A wrapper for UTF-8 Windows apps.

The Windows API is based on UTF-16 encoded wide text. For example, the API function CommandLineToArgvW that parses a command line, only exists in wide text version. But the introduction of support for UTF-8 as the process code page in the May 2019 update of Windows 10 now greatly increases the incentive to use UTF-8 encoded narrow text internally in in Windows GUI applications, i.e. using UTF-8 as the C++ execution character set also in Windows.

This article presents a minimal example of that (a message box with international text, using Windows’ char based API wrappers); shows one way to configure Windows with UTF-8 as the ANSI code page default; and shows how to build such a program with the MingGW g++ and Visual C++ toolchains.

This is discussed in that order in the following sections:

  1. A minimal example.
  2. The header wrappers.
  3. Configuring Windows with UTF-8 as the ANSI code page default.
  4. An application manifest resource specifying UTF-8.
  5. Building with MinGW g++ and with Visual C++.

I apologize for the less than perfect formatting and possible odd things. Every time I edit WordPress removes all instances of the text <windows.h> and wreaks havoc on the rest. This article was originally written as a GitHub-compatible markdown file but it turned out that markdown syntax highlighting, and a lot more, didn’t work in WordPress, so the text had to be very manually re-expressed as a sequence of WordPress “blocks”.

1. A minimal example.

With a suitable wrapper for <windows.h> the C++ code of a program that displays a Windows message box with international text can now be as simple as this:

minimal.cpp

#include <header-wrappers/winapi/windows-h.utf8.hpp>

auto main()
    -> int
{
    const auto& text    = "Every 日本国 кошка loves Norwegian blåbærsyltetøy, nom nom!";
    const auto& title   = "Some Norwegian, Russian & Chinese text in there:";
    MessageBox( 0, text, title, MB_ICONINFORMATION | MB_SETFOREGROUND );
}

Result when the program is built with a specification of UTF-8 as process code page, or alternatively is run in a Windows installation configured with UTF-8 as the ANSI code page default:

Image of OK messagebox

In contrast, here is what it looks like when a corresponding program using <windows.h> directly is built without a specification of UTF-8 as process code page and the Windows ANSI default is codepage 1252, Windows ANSI Western, as in the old days:

Image of ungood Windows ANSI Western messagebox

2. The header wrappers.

The wrapper <header-wrappers/winapi/windows-h.utf8.hpp> supports this new “like ordinary C++” kind of Windows application:

  • it increases the C++-compatibility of <windows.h> by suppressing the min and max macro definitions via option NOMINMAX and by asking for more strictly typed declarations via option STRICT, plus it reduces the size of this gargantuan include (e.g. just now from 80 287 lines to 54 426 lines, with MinGW g++), via option WIN32_LEAN_AND_MEAN,
  • it makes the char based …A-functions such as MessageBoxA available without suffix, i.e. for that example as just MessageBox, by ensuring that option UNICODE is not defined, and
  • it asserts that the effective process codepage is UTF-8, which it might or might not be.

header-wrappers/winapi/windows-h.utf8.hpp

#pragma once
#undef UTF8_WINAPI
#define UTF8_WINAPI
#include "windows-h.hpp"

namespace uuid_0985060C_1AAD_453C_B3F9_A2E543F4CF1E {
    struct Winapi_envelope
    {
        Winapi_envelope()
        {
            static const bool dummy = winapi_h_assert_utf8_codepage();
        }
    };
    
    static const Winapi_envelope ensured_globally_single_utf8_assertion{};
}  // namespace uuid_0985060C_1AAD_453C_B3F9_A2E543F4CF1E

The little complexity above could be avoided by using a C++17 inline variable. It would be more in the C++ spirit of coding to absolutely maximum performance and least verbosity, when there is a choice. However, many people are still stuck with earlier C++ standards, and though a fallback using static instead could be automatically provided, the header would then require Visual C++ 2019 users to add option /Zc:__cplusplus, which is not presently supported by the Visual Studio GUI.

Except for that issue the wrapper is designed to be a trivial top-level wrapper so that one can replace it with one’s own equally trivial top-level wrapper, for example in order to communicate a “not UTF-8 process code page” failure to the user in manner of one’s own choosing.

To wit, the wrapper delegates the first two points to a more basic wrapper <header-wrappers/winapi/windows-h.hpp>, which goes like this:

header-wrappers/winapi/windows-h.hpp

#pragma once
#ifdef MessageBox
#   error "<windows.h> has already been included, possibly with undesired options."
#endif

#include <assert.h>
#ifdef _MSC_VER
#   include <iso646.h>                  // Standard `and` etc. also with MSVC.
#endif

#ifndef _WIN32_WINNT
#   define _WIN32_WINNT     0x0600      // Windows Vista as earliest supported OS.
#endif
#undef WINVER
#define WINVER _WIN32_WINNT

#define IS_NARROW_WINAPI() \
    ("Define UTF8_WINAPI please.", sizeof(*GetCommandLine()) == 1)

#define IS_WIDE_WINAPI() \
    ("Define UNICODE please.", sizeof(*GetCommandLine()) > 1)

// UTF8_WINAPI is a custom macro for this file. UNICODE, _UNICODE and _MBCS are MS macros.
#if defined( UTF8_WINAPI) and defined( UNICODE )
#   error "Inconsistent encoding options, both UNICODE (UTF-16) and UTF8_WINAPI (UTF-8)."
#endif

#undef UNICODE
#undef _UNICODE
#ifdef UTF8_WINAPI
#   define _MBCS        // Mainly for 3rd party code that uses it for platform detection.
#else
#   define UNICODE
#   define _UNICODE     // Mainly for 3rd party code that uses it for platform detection.
#endif
#undef NOMINMAX
#define NOMINMAX
#undef STRICT
#define STRICT
#undef WIN32_LEAN_AND_MEAN
#define WIN32_LEAN_AND_MEAN
// After this an `#include <winsock2.h>` will actually include that header.

#include <windows.h>

inline auto winapi_h_assert_utf8_codepage()
    -> bool
{
    #ifdef __GNUC__
        #pragma GCC diagnostic push
        #pragma GCC diagnostic ignored "-Wunused-value"
    #endif
    assert(( "The process codepage isn't UTF-8 (old Windows?).", GetACP() == 65001 ));
    #ifdef __GNUC__
        #pragma GCC diagnostic pop
    #endif
    return true;
}

2. Configuring Windows with UTF-8 as the ANSI code page default.

For portability the program should best be built with UTF-8 process code page specified as an application manifest resource. Alternatively it will work to configure Windows with UTF-8 as the Windows ANSI default, provided it’s Windows 10 with the update of May 2019, or later. But probably few if any ordinary users will want to configure their Windows, or to let a program do that just in order to run that program.

You as developer may however find the convenience of UTF-8 as the Windows ANSI default, highly desirable.

It worked for me to change the item ACP to value 65001, in the semi-documented registry key

Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Nls\CodePage

You can change the value e.g. via the “regedit” GUI utility, or the reg command. You must then reboot Windows for the change to take effect.

And voilà! 🙂

But wait! …

Before doing that let’s build the program with a manifest that specifies UTF-8 as process code page. That way the program will work on any post-May-2019 Windows 10 installation, not just “it works on my computer!”. The <windows.h> wrapper shown above ensures that it will not mistakenly run and present gibberish on an earlier Windows version.

4. An application manifest resource specifying UTF-8.

An application manifest is an UTF-8 encoded XML file that, if properly magically named, can be just shipped with the application, but that’s best embedded as a resource in the executable.

The following manifest specifies both UTF-8 as process code page, and that the app uses version 6.0 or later of the Common Controls DLL, as opposed to an earlier version that has the same DLL name. The Common Controls DLL version gives a modern look and feel to buttons, menus, list, edit fields etc. Why that’s not the default, or why it requires this heavy machinery to specify, would be mystery if Microsoft were an ordinary company.

Anyway, the text:

resources/application-manifest.xml

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<assembly manifestVersion="1.0" xmlns="urn:schemas-microsoft-com:asm.v1">
    <assemblyIdentity type="win32" name="UTF-8 message box" version="1.0.0.0"/>
    <application>
        <windowsSettings>
            <activeCodePage xmlns="http://schemas.microsoft.com/SMI/2019/WindowsSettings"
                >UTF-8</activeCodePage>
        </windowsSettings>
    </application>
    <dependency>
        <dependentAssembly>
            <assemblyIdentity
                type="win32"
                name="Microsoft.Windows.Common-Controls"
                version="6.0.0.0"
                processorArchitecture="*"
                publicKeyToken="6595b64144ccf1df"
                language="*"
                />
        </dependentAssembly>
    </dependency>
</assembly>

Beware: at the time of writing there could be no whitespace such as space or newline on either side of the “UTF-8” activeCodePage value, and it had to be all uppercase.

5. Building with MinGW g++ and with Visual C++.

One way to include that text as a resource in the executable is to use a general resource script:

resources.rc

#include <windows.h>
1 RT_MANIFEST "resources/application-manifest.xml"

Here the 1 is the resource id, and the RT_MANIFEST is the resource type (as I recall from years ago RT_MANIFEST is defined as small integer, probably just 1).

With the MinGW GNU tools this script is compiled by windres into an apparently ordinary object file, which is just linked with the main program object file:

[G:\code\minimal_gui\binaries]
> set CFG=-std=c++17 -Wall -pedantic-errors

[G:\code\minimal_gui\binaries]
> g++ %CFG% ..\minimal.cpp -c -o minimal.o

[G:\code\minimal_gui\binaries]
> windres ..\resources.rc -o resources.o

[G:\code\minimal_gui\binaries]
> g++ minimal.o resources.o -mwindows

Here the -mwindows option specifies the GUI subsystem for the executable, so that Windows doesn’t pop up a console window when one runs the program from Windows Explorer.

With Microsoft’s tools the script is compiled by rc into a special binary resource format in a .res file, which is just linked with the main program object file. Options can be passed to the compiler cl.exe via the environment variable CL, and to the linker link.exe via the environment variable LINK. Using an obscure linker option is unfortunately necessary for building a GUI subsystem executable with a standard C++ main function with this toolchain:

[G:\code\minimal_gui\binaries]
> set CL=^
More? /nologo ^
More? /utf-8 /EHsc /GR /FI"iso646.h" /std:c++17 /Zc:__cplusplus /W4 ^
More? /wd4459 /D _CRT_SECURE_NO_WARNINGS /D _STL_SECURE_NO_WARNINGS

[G:\code\minimal_gui\binaries]
> cl ..\minimal.cpp /c
minimal.cpp

[G:\code\minimal_gui\binaries]
> rc /nologo /fo resources.res ..\resources.rc

[G:\code\minimal_gui\binaries]
> set LINK=/entry:mainCRTStartup

[G:\code\minimal_gui\binaries]
> link /nologo minimal.obj resources.res user32.lib /subsystem:windows /out:b.exe

Microsoft now also has special tools (or maybe a special tool) to handle application manifests, but I haven’t used that.

UTF-8 in the Windows API

The May 2019 update of Windows 10 introduced the possibility of setting the ActiveCodePage property of an executable to UTF-8. This is done via the application manifest. The documentation is super-vague on the technical details and history, and in usual Microsoft fashion the functionality is obscured and the little desirable kill-a-gnat can only be done by costly nuclear bombing, so to speak — why let something simple be simple if it can be wrapped in military standard complexity?

But it means that with Visual C++ 2019 one can now use UTF-8 encoding for GUI applications, and for the output of console programs, without any encoding conversions in the code.

In particular, with UTF-8 active process codepage the arguments of main now come handily UTF-8 encoded, which means that they can now represent general filenames also in Windows. Hurray! Yippi!

However, interactive console input of UTF-8 is still limited to ASCII at the API-level. And the MinGW g++ 9.2 compiler’s default standard library implementation doesn’t support UTF-8 in the C and C++ locale machinery, e.g in setlocale, probably because it employs an old version of Microsoft’s runtime library. That means that FILE* or iostreams UTF-8 console output with MinGW g++ 9.2 only works for the default “C” locale.

I experimented by setting the ANSI codepage default in the registry to 65001, the UTF-8 codepage number. After rebooting the console windows came up with active codepage 65001, even though the OEM codepage default was the same old one (850 in my case). That indicates an effort on Microsoft’s part to support UTF-8 all the way in Windows, which if so is fantastically good.


An example application manifest.

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<assembly manifestVersion="1.0" xmlns="urn:schemas-microsoft-com:asm.v1">
    <assemblyIdentity type="win32" name="UTF-8 app example" version="6.0.0.0"/>
    <application>
        <windowsSettings>
            <activeCodePage xmlns="http://schemas.microsoft.com/SMI/2019/WindowsSettings"
                >UTF-8</activeCodePage>
        </windowsSettings>
    </application>
    <dependency>
        <dependentAssembly>
            <assemblyIdentity
                type="win32"
                name="Microsoft.Windows.Common-Controls"
                version="6.0.0.0"
                processorArchitecture="*"
                publicKeyToken="6595b64144ccf1df"
                language="*"
                />
        </dependentAssembly>
    </dependency>
</assembly>

The second assemblyIdentity part has nothing to do with the UTF-8 support, it just corrects a practically unusable default for the look and feel of buttons etc. Essentially this manifest corrects the two “wrong” defaults: the narrow text encoding, and the look ’n feel. From within an application with this manifest it looks as both CP_ACP (the global default) and CP_THREAD_ACP (the mysterious thread codepage) are UTF-8, codepage 65001.

In my experimentation UTF-8 had to be specified in uppercase, and it did not work with whitespace such as space or newline at either side.


An example resource script:

#include <windows.h>
1 RT_MANIFEST "resources/application-manifest.xml"

Why COW was deemed ungood for std::string.

COW, short for copy on write, is a way to implement mutable strings so that creating strings and logically copying strings, is reduced to almost nothing; conceptually they become free operations like no-ops.

Basic idea: to share a data buffer among string instances, and only make a copy for a specific instance (the copy on write) when that instance’s data is modified. The general cost of this is only an extra indirection for accessing the value of a string, so a COW implementation is highly desirable. And so the original C++ standard, C++98, and its correction C++03, had special support for COW implementations, and e.g. the g++ compiler’s std::string implementations used COW.

So why was that support dropped in C++11?

In particular, would the same reason or reasons apply to a reference counted immutable string value class?

As we’ll see it does not, it’s just a severe mismatch between the std::string design and the ideal COW requirements. But it took a two hour car trip, driving 120 kms on winter roads, for my memory to yet again cough up the relevant scenario where Things Go Wrong™. I guess it’s like the “why can’t I assign a T** to a T const** question; it’s quite counter-intuitive.

Basic COW string theory: the COPOW principle.

A COW string has two possible states: exclusively owning the buffer, or sharing the buffer with other COW strings.

It starts out in state owning. Assignments and copying initializations can make it sharing. Before executing a “write” operation it must ensure that it’s in owning state, and a transition from sharing to owning involves copying the buffer contents to a new and for now exclusively owned buffer.

With a string type designed for COW any operation will be either non-modifying, a “read” operation, or directly modifying, a “write” operation, which makes it is easy to determine whether the string must ensure state owning before executing the operation.

With a std::string, however, references, pointers and iterators to mutable contents are handed out with abandon. Even a simple value indexing of a non-const string, s[i], hands out a reference that can be used to modify the string. And so for a non-const std::string every such hand-out-free-access operation can effectively be a “write” operation, and would have to be regarded as such for a COW implementation (if the current C++ standard had permitted a COW implementation, which it doesn’t).

I call this the principle of copy on possibility of write, or COPOW for short. It’s for strings that aren’t designed for COW. For a COW-oriented design applying COPOW reduces to pure COW.

A code example showing how COW works.

To keep the size of the following example down I don’t address the issue of constant time initialization from literal, but just show how assignment and copy initialization can be reduced to almost nothing:

#include <cppx-core/_all_.hpp>  // https://github.com/alf-p-steinbach/cppx-core

using C_str = const char*;      // Is also available in cppx.

namespace my
{
    $use_cppx( Raw_array_of_, Size );
    $use_std( begin, end, make_shared, vector, shared_ptr );

    class Cow_string
    {
        using Buffer = vector<char>;

        shared_ptr<Buffer>      m_buffer;
        Size                    m_length;

        void ensure_is_owning()
        {
            if( m_buffer.use_count() > 1 )
            {
                m_buffer = make_shared<Buffer>( *m_buffer );
            }
        }

    public:
        auto c_str() const
            -> C_str
        { return m_buffer->data(); }

        auto length() const
            -> Size
        { return m_length; }

        auto operator[]( const Size i ) const
            -> const char&
        { return (*m_buffer)[i]; }

        auto operator[]( const Size i )
            -> char&
        {
            ensure_is_owning();
            return (*m_buffer)[i];
        }

        template< Size n >
        Cow_string( Raw_array_of_<n, const char>& literal ):
            m_buffer( make_shared<Buffer>( literal, literal + n ) ),
            m_length( n - 1 )
        {}
    };
}  // namespace my

Here assignment is the default-generated assignment operator that just assigns the data members m_buffer and m_length, which are a shared_ptr and an integer, and ditto for copy initialization.

And apparently this code abides by the COPOW principle, so it should be safe…

The problem: UB by adding code that just copies.

Consider the following usage code, it’s perfectly fine:

auto main() -> int
{
    my::Cow_string s = "Du store Alpakka!";
    const C_str p = s.c_str();

    // In this block the contents of `s` are not modified.
    {
        $use_std( ignore );
        const char first_char = s[0];
        ignore = first_char;
    }

    $use_std( cout, endl );
    cout << p << endl;
}

This code is fine because the COW string is already in state owning when s[0] is executed on the non-const s. So all that the initialization of first_char does is to copy a char value. Fine.

But if a maintainer innocently just introduces a logical copy of the string value, which is what COW primarily optimizes, and which certainly doesn’t change the conceptual value, then mayhem ensues:

auto main() -> int
{
    my::Cow_string s = "Du store Alpakka!";
    const C_str p = s.c_str();

    // In this block the contents of `s` are not modified.
    {
        $use_std( ignore );
        my::Cow_string other = s;
        ignore = other;

        const char first_char = s[0];
        ignore = first_char;
    }

    $use_std( cout, endl );
    cout << p << endl;      //! Undefined behavior, p is dangling.
}

Uh oh.

Since s here is in state sharing, the COPOW principle makes the s[0] operation copy the shared buffer, to become owning. Then at the end of the block the only remaining owner of the original buffer, the other string, is destroyed, and destroys the buffer. Which leaves the p pointer dangling.

For a custom string type like Cow_string this is a user error. The type is just badly designed, so that it’s very easy to inadvertently use it incorrectly. But for a std::string it’s formally a bug in the COW implementation, a bug showing that COPOW is just not enough.

For a std::string, if the standard had permitted a COW implementation, to avoid the above calamity it would be necessary to transition to the owned state, incurring an O(n) copying of string data, every place that a reference, pointer or iterator is handed out, regardless of const-ness of the string. One could maybe call that copy on handing out any reference, COHOAR. It greatly reduces the set of cases where COW has an advantage. The C++ standardization committee deemed that cost too high, the remaining advantages of COW too low, to continue supporting COW. So,

  • the C++03 wordings that supported COW were removed;
  • wording was introduced, especially a general O(1) complexity requirement for [] indexing, that disallowed COW; and
  • functionality such as string_view was added, that relies on having pointers to string buffers, and that itself hands out references.

What about threads?

It’a common misconception that COW std::strings would be incompatible with multi-threading, or that making it compatible would make it inefficient, because with COW ordinary copying of a string doesn’t yield an actual copy that another thread can access freely.

In order to allow string instances that are used by different threads, to share a buffer, just about every access function, including simple [] indexing, would need to use a mutex.

However, a simple solution is to just not use ordinary copy initialization or assignment to create a string for another thread, but instead a guaranteed content copying operation such as std::string::substr, or initialization from iterator pair. The C++11 standard could have gone in this other direction. It could, in principle, have added to the existing C++03 support for COW strings, noting that COHOAR, not just COPOW, is required, and added a dedicated deep-copy operation or deep-copy support type plus wording about thread safety.

What about reference counted immutable strings?

An immutable string is a string type such as the built in string types in Java, C# or Python, where the available operations don’t support string data modification. Strings can still be assigned. One just can’t directly change the string data, like changing “H” to ”J“ in “Hello”.

Immutable strings can and in C++ typically will share their string data via reference counting, just as with COW strings. As with COW strings they support amortized constant time initialization from literal, ditto superfast copy assignment and copy initialization, and in addition, if strings don’t need to be zero-terminated they support constant time substring operations. They’re highly desirable.

So, is the problem shown above, a showstopper for immutable strings in C++?

Happily, no. The problem comes about because std::string hands out references, pointers and iterators that can be used to change the string data without involving std::string code, i.e. without its knowledge. That can’t happen with an immutable string.

And figuring out this, whether there was a showstopper, and whether std::string_view (that hands out references) could be used freely in code that would deal with immutable strings, was the reason that I delved into the question of COW std::string again. At one point, long ago, I knew, because I participated in some debates about it, but remembering the problematic use case wasn’t easy. It’s just not intuitive to me, that adding an operation that just copies, can create UB…

Non-crashing Python 3.x output in Windows

Non-crashing Python 3.x output in Windows

Problem

The following little Python 3.x program just crashes with CPython 3.3.4 in a default-configured English Windows:

crash.py3
#encoding=utf-8
print( "Blåbærsyltetøy!")
H:\personal\web\blog alf on programming at wordpress\001\test>chcp 437
Active code page: 437

H:\personal\web\blog alf on programming at wordpress\001\test>type crash.py3 | display_utf8
#encoding=utf-8
print( "Blåbærsyltetøy!")

H:\personal\web\blog alf on programming at wordpress\001\test>crash.py3
Traceback (most recent call last):
  File "H:\personal\web\blog alf on programming at wordpress\001\test\crash.py3", line 2, in 
    print( "Blåbærsyltet\xf8y!")
  File "C:\Program Files\CPython 3_3_4\lib\encodings\cp437.py", line 19, in encode
    return codecs.charmap_encode(input,self.errors,encoding_map)[0]
UnicodeEncodeError: 'charmap' codec can't encode character '\xf8' in position 12: character maps to 

H:\personal\web\blog alf on programming at wordpress\001\test>_

Here codepage 437 is the original IBM PC character set, which is the default narrow text interpretation in an English Windows console window.

A partial solution is to change the default console codepage to Windows ANSI, which then at least for CPython matches the encoding for output to a pipe or file, and it’s nice with consistency. But also this has a severely limited character set, with possible crash behavior for any unsupported characters.

Direct console output

Unicode text limited to the Basic Multilingual Plane (essentially original 16-bits Unicode) can be output to a Windows console via the WriteConsoleW Windows API function.

The standard Python ctypes module provides access to the API:

Direct_console_io.py
import ctypes
class Object: pass

winapi = Object()
winapi.STD_INPUT_HANDLE     = -10
winapi.STD_OUTPUT_HANDLE    = -11
winapi.STD_ERROR_HANDLE     = -12
winapi.GetStdHandle         = ctypes.windll.kernel32.GetStdHandle
winapi.CloseHandle          = ctypes.windll.kernel32.CloseHandle
winapi.WriteConsoleW        = ctypes.windll.kernel32.WriteConsoleW

class Direct_console_io:
    def write( self, s ) -> int:
        n_written = ctypes.c_ulong()
        ret = winapi.WriteConsoleW(
            self.std_output_handle, s, len( s ), ctypes.byref( n_written ), 0
            )
        return n_written.value

    def __del__( self ):
        if not winapi: return       # Looks like a bug in CPython 3.x
        winapi.CloseHandle( self.std_error_handle )
        winapi.CloseHandle( self.std_output_handle )
        winapi.CloseHandle( self.std_input_handle )

    def __init__( self ):
        self.dependency = winapi
        self.std_input_handle   = winapi.GetStdHandle( winapi.STD_INPUT_HANDLE )
        self.std_output_handle  = winapi.GetStdHandle( winapi.STD_OUTPUT_HANDLE )
        self.std_error_handle   = winapi.GetStdHandle( winapi.STD_ERROR_HANDLE )

Implementing input is left as an exercise for the reader.

Overriding the standard streams to use direct i/o and UTF-8.

In addition to the silly crashing behavior, the standard streams in CPython 3.x, like sys.stdout, default to Windows ANSI for output to file or pipe. In Python 2.7 this could be reset to more useful UTF-8 by reloading the sys module in order to get back a dynamically removed method that could set the default encoding. No longer in Python 3.x, so this code just creates new stream objects:

Utf8_standard_streams.py
import io
import sys
from Direct_console_io import Direct_console_io

class Dcio_raw_iobase( io.RawIOBase ):
    def writable( self ) -> bool:
        return True

    def write( self, seq_of_bytes ) -> int:
        b = bytes( seq_of_bytes )
        return self.dcio.write( b.decode( 'utf-8' ) )

    def __init__( self ):
        self.dcio = Direct_console_io()

class Dcio_buffered_writer( io.BufferedWriter ):
    def write( self, seq_of_bytes ) -> int:
        return self.raw_stream.write( seq_of_bytes )

    def flush( self ):
        pass

    def __init__( self, raw_iobase ):
        super().__init__( raw_iobase )
        self.raw_stream = raw_iobase

# Module initialization:
def __init__():
    using_console_input = sys.stdin.isatty()
    using_console_output = sys.stdout.isatty()
    using_console_error = sys.stderr.isatty()

    if using_console_output:
        raw_io = Dcio_raw_iobase()
        buf_io = Dcio_buffered_writer( raw_io )
        sys.stdout = io.TextIOWrapper( buf_io, encoding = 'utf-8' )
        sys.stdout.isatty = lambda: True
    else:
        sys.stdout = io.TextIOWrapper( sys.stdout.detach(), encoding = 'utf-8-sig' )

    if using_console_error:
        raw_io = Dcio_raw_iobase()
        buf_io = Dcio_buffered_writer( raw_io )
        sys.stderr = io.TextIOWrapper( buf_io, encoding = 'utf-8' )
        sys.stderr.isatty = lambda: True
    else:
        sys.stderr = io.TextIOWrapper( sys.stderr.detach(), encoding = 'utf-8-sig' )
    return

__init__()

Disclaimer: It’s been a long time since I fiddled with Python, so possibly I’m breaking a number of conventions plus doing things in some less than optimal way. But this was the first path I found through the jungle of apparently arbitrary io class derivations etc. It worked well enough for my purposes (in a little script to convert NRK’s HTML-format subtitles to SubRip format), so, I gather it can be useful also for you – at least as a basis for more robust and/or more general code.

2013 in review

The WordPress.com stats helper monkeys prepared a 2013 annual report for this blog.

Here’s an excerpt:

The concert hall at the Sydney Opera House holds 2,700 people. This blog was viewed about 10,000 times in 2013. If it were a concert at Sydney Opera House, it would take about 4 sold-out performances for that many people to see it.

Click here to see the complete report.

2012 in review

The WordPress.com stats helper monkeys prepared a 2012 annual report for this blog.

Here’s an excerpt:

600 people reached the top of Mt. Everest in 2012. This blog got about 10,000 views in 2012. If every person who reached the top of Mt. Everest viewed this blog, it would have taken 17 years to get that many views.

Click here to see the complete report.

C++11 features in Visual C++, yeah!

Recently Microsoft surprised me – positively! – with supporting newfangled C++11 features in the November CTP of their Visual C++ 11.0 compiler:

  • Variadic templates
  • Uniform initialization and initializer_lists
  • Delegating constructors
  • Raw string literals
  • Explicit conversion operators
  • Default template arguments for function templates

The library has not yet been updated to take advantage, but still this means that it’s now possible to avoid macro hell for things such as makeUnique (but unforutunately not yet for e.g. platform-specific Unicode strings, no support yet for the newfangled literals).

On the other hand, Visual C++ implements the regexp library, while g++ does not. And Visual C++ has working exceptions, while AFAIK the dang[1] compiler still has not. So this may just look as if Visual C++ is now overtaking g++ and the dang compiler in the race to support the C++11 standard! 🙂

[1] As Brian Keminghan remarked, dang if I can remember its name!

Liskov’s substitution principle in C++ <

Part I of III: The LSP and value assignment.

Abstract:
Liskov’s principle of substitution, a principle of generally good class design for polymorphism, strongly implies the slicing behavior of C++ value assignment. Destination value slicing can cause a partial assignment, which can easily break data integrity. Three solutions are (1) static checking of assignment, (2) dynamic checking of assignment, and (3), generally easiest, prohibiting assignment, then possibly providing cloning functionality as an alternative.

Contents:

  • > A short review of the LSP.
  • > How the LSP (almost) forces slicing in C++.
  • > The danger of slicing: type constraint violations.
  • > The possible design alternatives wrt. providing value assignment.
  • > How to provide assignment with STATIC CHECKING of type constraints.
  • > How to provide assignment with DYNAMIC CHECKING of type constraints.
  • > How to provide CLONING as an alternative to assignment.

Continue reading

ResultOf a function with C++11

Using std::result_of requires you to specify the function argument types. Which is not very practical when you don’t know the function signature. Happily @potatoswatter (David Krauss) over at Stack Overflow pointed out to me that std::function provides the desired functionality:

template< class Func >
struct ResultOf
{
    typedef typename std::function<
        typename std::remove_pointer<Func>::type
        >::result_type T;
};

Mainly, this saves one from writing a large number of partial specializations for Visual C++ 10.0, which lacks support for C++11 variadic templates.

– Enjoy!