Was at a PHP meetup where the group was discussing Docker. Members and the presenter knew certain Linux distributions had a smaller footprint for use with Docker. I was surprised to find out they really didn't know why that was. One of the key factors is the C runtime library. Basic C runtime libraries just cover the functions and data structures that are part of the ISO C standard. Many C runtime libraries also add functions and data structures that are part of the POSIX standard as documented by the Open Group. Some C runtime libraries are rather bloated and provide a wide variety of functions (even beyond those documented by the ISO C and POSIX standards). Others provide a bare minimum. Some, especially those targeting embedded systems are designed for efficiency. Others are designed for functionality. Some provide no Unicode support (locale 'C' only). Some like musl, concentrate on UTF-8 support. Some try to support a large variety of characters sets and internationalization features. All these factors can affect code size and efficiency when compiling programs.

Alpine Linux previously used the uclibc runtime library and now uses the musl library. Most major Linux distributions use glibc. It was a big step, but a positive one when Debian (and Ubuntu) made the switch to eglibc. The choice of C runtime library can make a huge difference for the operating system.

For Windows developers, if you're using MinGW, the GNU compiler on Windows, you're using the Microsoft runtime libraries. The original version of MinGW used crtdll.dll but later versions use msvcrt.dll. Windows systems typically have one of these runtime libraries already installed. So while, you can't distribute Microsoft's libraries, you really don't have to. At least one is already on any particular Windows system. It gets even more complicated because different versions of Windows have different versions of msvcrt (such as msvcr70.dll, msvcr80.dll). MinGW uses a subset of the runtime functions based on Visual Studio 6.0. There are ways to access runtime functions from later versions of Visual Studio, but the application becomes less portable to various versions of Windows. Cygwin which also works on Windows, avoids the problem of dealing with multiple Windows runtime libraries and dlls and provides better POSIX compatibility for their runtime library by using a runtime library based on newlib.

There are a wide variety of runtime libraries designed for embedded systems. They're typical more compact and less bloated than a library like glibc and many are easier to port to various platforms. Of the runtime libraries available for embedded systems that are highly portable, I thought the newlib design was interesting. newlib is currently maintained by Red Hat. There are a limited number of syscalls (typically functionality provided by the kernel) that one needs to provide code for to get the library to work. Newlib uses a combination of public domain and BSD style licenses. Cygwin uses a runtime library derived from newlib, but adds several POSIX functions. It also uses a GNU GPL license. That means whenever you distribute programs linked with their runtime library you must also distribute the source code in order to be compliant with the GPL license.

As mentioned, the standard C library on most Linux distributions is glibc which was developed by the Free Software Foundation. The glibc project was slow to take patches and is a rather large library, so some distributions switched to eglibc which is binary compatible with glibc. The binary compatibility makes it easy to switch between the two. Some Linux distributions wanted to avoid bloated C libraries and work well on low resource or older systems. They chose uclibc which was designed for embedded systems. When I worked with a uclibc based distribution, I found myself making several patches to Open Source programs just to get them to compile. Many Linux distributions such as Alpine Linux are now using musl. It's designed for efficiency and standards compliance including full POSIX standards compliance.

musl was designed to work with a Linux kernel. So unlike choices such as newlib, it is not easy to port to other operating systems. The midipix project is endeavoring to create a POSIX compatible layer for Windows, so that musl will work out of the box on that system. Musl uses a MIT license. The midipix project will use a more restrictive license similar to Cygwin. Many basic embedded system libraries tend to use less restrictive licenses like MIT and BSD so that they will be adopted by companies. However, project or company adapts a C library to a particular system and adds a lot of functionality, they typically tend to use GNU GPL or other more restrictive licenses. Many projects dual license in hopes of selling companies a commercial license with less restrictions.

Google developed the Bionic C library for it's Android operating systems. It has a BSD license. It's also designed to work on low resource systems so it tends to offer less functionality than other C libraries such as glibc. It has partial POSIX support.

I've been hitting many limitations with the MinGW runtime libraries when it comes to porting. Alternatives such as Cygwin's or midipix's runtime libraries would overcome the issues. However, the licenses are much more restrictive. I know I definitely wanted more POSIX compatibility on Windows than MinGW offers out of the box. As a cross-platform programmer, it would be nice to take whatever C runtime library I end up with on Windows and reuse it on Linux and other systems. I looked at C runtime libraries for embedded systems which typically port well. Of those, newlib seemed the most interesting, because according to some of the documentation it only requires 17 syscalls to port it to an operating system. Some Windows CE compiler ports use newlib with added functionality for the Windows CE operating system to derive a working C/C++ compiler. When I investigated the newlib code, I did not particularly like the design, especially the way it handled threading by providing standard and threaded versions of functions. The implementation of file I/O looked like it had been modified several times and at this point could use a major refactoring. When I read some of the comments in that section of the code, I felt very uncomfortable using the library. I wanted a simple, clean, basic design that I can add to.

Another option I looked at was PDClib. I love the idea of a public domain library. MinGW original licensed their WIN32 and runtime code (which integrates with Microsoft's code) as public domain.
PDCLib was based on an earlier Public Domain library project originally at Sourceforge. I tried PDClib on Windows (which the developer says he uses it with), but I was unable to get file I/O to work properly. I contacted the developer to see if he needed with the project, but he really didn't seem to need any assistance at the time. PDClib only supports standard C functions. It does not provide any POSIX functionality. So, it would have limited usage as is for running most Open Source programs.

A number of original operating systems use their own C runtime libraries. I figure, if they can reinvent the wheel and create a C runtime library for their particular purposes, so can I.

I've been coding functions that are typically part of the C runtime library in order to provide better porting support for Windows. I wrote a C11 compatible thread library, several BSD and POSIX string functions, some POSIX file functions, etc. That left me with the dilemma of how best to integrate the additions with the runtime library. They really should be part of the library and part of the C standard headers. I currently have them implemented as supplemental libraries that have to be added separately. It's easier to test and integrate on various operating systems that way. Ideally, it would be nice to have everything accessible as one library though.

I'm very familiar in the various methods of connecting to the kernel in Windows. Some projects such as midipix just use ntdll.dll. Other projects connect to other Microsoft dlls such as kernel32.dll. One can use LoadLibrary, GetProcAddress to connect t a dll or if the library is already linked in, one can skip LoadLibrary. A few Open Source projects I've seen actually implement the LoadLibrary functionality from scratch. I'm not as familiar with the techniques to connect to the Linux, BSD and other kernels and would love to find more clear documentation on this subject. If you run across any good materials, please let me know ( http://www.distasis.com/connect.htm ). Linux uses techniques such as vdso, vsyscall, syscall to call kernel functions.

I find it fascinating to consider the design trade-offs of various C runtime libraries. With that in mind, here's a list of some of the C runtime library options:


Linux from Scratch build instructions (including musl)
BSD regular expression library
(Musl regular expression support was forked from this library.)

Original Public Domain C library:
libTom Public Domain libraries for math and cryptographics functions
(Some of musl's functions were forked from these.)



Windows CE cross-compiler:


I've been looking for useful, efficient, user-friendly alternatives to build tools like GNU autotools and cmake. I've even created lists of build tool alternatives at various wikis and sites related to programming and compilers. If there's interest, I can post some of that information here along with pros and cons of various tools. I think, during my searches, I've found some good alternatives for my own projects and to use with my own build script generator.

If you're looking for build tools for your own projects, you may want to try the following tools. I'm also doing some active development and patching to some of the tools and would be interested in comparing notes with others on ways to use and improve them (see below for details).

GNU autotools is probably the most popular build system for most C/C++ programs. So, what's wrong with it? Just to build a C program, you need two interpreters (m4 and Perl). You also need autoconf, automake and make. The input to these programs is not necessarily intuitive to a C programmer. Many C programs, especially those using Qt make use of cmake which has less dependencies, but I've also found it less than intuitive. What if you want to build a system from scratch. You can get make to build without any other build tools. I've done it. From there, you can work to build the rest of the gnu autotools toolchain. To build cmake, you need to bootstrap the build using another instance of cmake. So where do you get the original build of cmake for the system? There is a way to build cmake with gnu autotools, but I've found it rather buggy.

After looking through several make alternatives, I really have not found a good replacement for it. The syntax takes some getting used to, but I've been able to find ways to get it do whatever I need it to do. There are situations where make is very inefficient, but there are work-arounds. Efficiency really depends on how well you craft your makefiles. I attempted to find some alternatives to the GNU version of make. BSD make has very different syntax, so only the simplest make scripts work with both tools. I find GNU make used more often than BSD make for building Open Source projects and it has features that were never added to BSD make. There's a Perl implementation of make, but that requires a Perl interpreter. My main issue with GNU make is that it is only supported on certain platforms. I sent in a bug report about GNU make not working properly on native Windows and I even sent in a patch. The developers were not interested in supporting native Windows. They thought it was enough that there were versions that worked with Cygwin and msys. Unfortunately, I've yet to find an alternative to make that handles the GNU makefile sysntax and doesn't require installation of an interpreter.

I've decided that until I can find anything better, I will continue to use GNU make. Since it is Free Software, I can modify the code to work on other systems that GNU make developers don't care to support. I can distribute the modified version if I distribute the source code. So, I use a modified version of GNU make that fixes platform specific bugs that I've encountered.

After searching through many alternatives, I've found a wonderful replacement to configure/autoconf. It's also more compact and I find it more intuitive than cmake. It's called CDetect. It's written in C and is comprised of only 3 files. The project is no longer actively developed. However, I've been making several modifications of my own to get it to suit my projects' needs. I've implemented some of the items on the original developers To Do lists. I'm still making modifications as I find features that are lacking, but it makes a useful replacement to configure. I've converted some of the Open Source projects I build from source regularly to use CDetect and custom makefiles instead of their build systems. If you're building from source, such as with a Linux from Scratch system, using CDetect means you don't need Perl, and several other programs installed just to build a C/C++ program.

Freedesktop.org advocates the use of pkg-config. It's used by many GNU projects as well. While I originally thought it was yet another complication when building from source, I've found pkg-config rather useful in simplifying build scripts. You don't have to worry about finding the right library, pkg-config can tell you where to find it. If you're cross-compiling, you can get have two sets of directories with pkg-config information, one for cross-compiled libraries and one for regular libraries. Change the path in an environment variable and your build script knows where to find the appropriate libraries. What I really didn't like about pkg-config was the complexity of the program and that it required a circular dependency with glib. I don't even want glib on my system at this point. Luckily, there is an alternative with friendly licensing called pkgconf. It's a drop in replacement for pkg-config. It's very helpful in finding where the right libraries are on a system. I've gone from never using pkg-config to use pkgconf in almost all my build scripts.

So, between CDetect, pkgconf and make, I now have all the tools I need to use with my build system in order to build the Open Source programs and libraries I use most in an automated fashion. The tools are all written in C, so they require no special interpreters or other languages just to build them.

If you'd like to try out CDetect with my patches or see some of the build scripts I'm using with these tools, check out the archive link on my LM BLD system page:

I've added several features to my patched version of CDetect. Check the notes.txt file for details. I'm currently making some new modifications and would love input from other developers/users. If you'd like to make suggestions or compare notes, please contact me through the CppDesign mailing list or my web site:
GUI libraries

I've written articles on cross platform screen libraries including one for the C/C++ Users Journal. I've also done a lot of searching and evaluation of cross-platform GUI libraries. You can take a look at my comparison article on screen libraries at http://www.distasis.com/cpp/scrlib.htm

The following list does not cover every GUI library out there, but it gives a good sample of what's available. Most are C++ libraries but there are a few C libraries for those wanting to work only with C.

My personal preferences at this point are SDL (1 and 2), pdcurses and FLTK because they're lightweight and work on a large variety of systems including mobile devices.

URLs are accurate as of when this was posted. However, they can change over time. You can use a search engine or archive.org wayback tool to find pages that have been moved or backups of older versions of pages.

FLTK - Fast Light ToolKit (C++)

Fox Toolkit (C++)

wxWidgets (C++)

SDL - SDL 1 and SDL 2
Simple DirectMedia Layer - C cross-platform multimedia library

C++ library

SMFL - simple and fast multimedia library

C library
Works with Windows console, X11, SDL 1 and 2

pdcurses win32a
C library
A PDCurses fork for Win32 (not console mode).

Expansive C++ GUI toolkit - source includes many libraries including a browser example using Webkit.

C console library. Works on POSIX systems and Windows.

I learned a great deal about Win32 C++ programming from the book that created this framework:

Borland's Object Windows C++ Library for the modern age

C++ cross-platform rapid application development framework

C++ library

C++11 GUI library

Toolkit for platform-independent graphical user interface programming in the C language.
Works with Windows and X Windows

Anti-Grain Geometry
C++ free graphics library for Windows and X11. Includes SVG viewer.

Crazy Eddie's GUI System C++ library providing windowing and widgets for graphics APIs/engines

Portable C++ gaming library for Allegro, SDL and/or OpenGL

C/C++ GUI library for OpenGL and DirectX applications.

C Cross-platform toolkit for graphical applications.
Difficult to build on some systems and some versions can be buggy.

LibUFO Universal Form Objects, C++ core library for forms.

C++ V GUI library and IDE (VIDE).

Multi-platform toolkit for building graphical user interfaces. with API in three languages: C, Lua and LED.

Milkymist GUI toolkit
C GUI library

Mini Interative Interface Toolkit Library

Funny tool kit, a C cross-platform embedded GUI
I'm working on several projects. One of my goals is to be able to port any of the SDL 1.2.x programs I use so they'll work with SDL 1.2.15 or with SDL 2.x. So far, I've added SDL 2 support to PDCurses. I believe some or all of those patches made it back into the official version. Other programs I've added SDL2 support for include bard, picaxo, sfontview, unifontview, perigee, SDL_Draw, pong, drac, yahtzee. More are in the works including Tuxmath. Bard is a lightweight epub reader with text to speech support. Picaxo is a lightweight graphics viewer. Sfontview is a lightweight TrueType font viewer. Unifontview is a font viewer that shows a font's entire character set including Unicode characters supported. Perigee is a graphics slideshow program. SDL_Draw is a graphics library for simple line drawing with SDL. I'm currently using it with wavetools to do the line drawing for a lightweight wave file viewer. The wave file viewer also builds with SDL 1.2.x or SDL 2.x.

Code/patches for many of the modifications I've made are available from a link at:
I'll be adding more modifications to various projects over time. Feel free to write if you're interesting in discussing a particular SDL 2 conversion further.


May. 5th, 2016 12:29 pm
There are now several forks of MinGW and each has its pros and cons. However, there are now enough negatives to using them, that I've found it necessary to build MinGW from scratch myself. The MinGW64 project uses a later version of gcc, has better compatibility for building Open Source projects and has its own thread library instead of using Red Hat's pthreads-w32. Some custom builds of MinGW64 even have POSIX threading set as the default instead of Win32 threading. That means better compatibility for C++ thread related code (since the GNU C++ library relies on POSIX threading for parts of its implementation). The MinGW project has always been more careful about licensing and making sure that the code it was using was properly licensed and legal for usage. The MinGW project did follow the example of the MinGW64 project in one key area. They switched from public domain to a MIT license for their runtime library and Win32 API. When they did so without clearly indicating that an exception could be made similar to the GNU gcc runtime license exception, I felt it was time to stop using that version of the MinGW compiler.

I'm currently working with gcc 4.9.2 compiled from source. I'm still using the older public domain APIs, but I've made several modifications for compatibility with the Win32 API (including some modifications that aren't available in the MinGW64 libraries). I have a minimal thread library that was custom written for portability. It's based on C11 thread support and includes POSIX functionality. The gnu compiler is built with POSIX threads as the default so C++ threading works as expected.

So far, I've had no reason to want to work with any other MinGW forks. The version I have does everything I need and supports all the programs I want to compile on Windows. My particular fork is continually evolving. I continue to add support for new Win32 API changes, Win32 API omissions, new C/C++ features as I need them. At some point, I hope to completely replace the runtime library with code that better supports internationalization (better UTF-8 support), C standard compatibility and other useful features.

If anyone else is finding limitations with the compilers maintained by the various MinGW and MinGW64 projects or other related forks based on these projects, I highly recommending building the GNU compiler from source on your own with the options you need most. If you're interested in discussing the GNU compiler further or want to know more about my modifications, you're welcome to use the CppDesign mailing list ( http://groups.yahoo.com/group/CppDesign ) as a forum for further discussion.

July 2017

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