For our current project, we are thinking to use Boost framework.
However, the project should be truly cross-platform and might be shipped to some exotic platforms. Therefore, we would like to use only Boost packages (libraries) that does not contain any platform specific code: pure C++ and that's all.
Boost has the idea of header-only packages (libraries).
Can one assume that these packages (libraries) are free from platform specific code?
In case if not, is there a way to identify these kind of packages of Boost?
All C++ code is platform-specific to some extent. On the one side, there is this ideal concept of "pure standard C++ code", and on the other side, there is reality. Most of the Boost libraries are designed to maintain the ideal situation on the user-side, meaning that you, as the user of Boost, can write platform-agnostic standard C++ code, while all the underlying platform-specific code is hidden away in the guts of those Boost libraries (for those that need them).
But at the core of this issue is the problem of how to define platform-specific code versus standard C++ code in the real world. You can, of course, look at the standard document and say that anything outside of it is platform-specific, but that's nothing more than an academic discussion.
If we start from this scenario: assume we have a platform that only has a C++ compiler and a C++ standard library implementation, and no other OS or OS-specific API to rely on for other things that aren't covered by the standard library. Well, at that point, you still have to ask yourself:
What compiler is this? What version?
Is the standard library implementation correct? Bug-free?
Are those two entirely standard-compliant?
As far as I know, there is essentially no universal answer to this and there are no realistic guarantees. Most exotic platforms rely on exotic (or old) compilers with partial or non-compliant standard library implementations, and sometimes have self-imposed restrictions (e.g., no exceptions, no RTTI, etc.). An enormous amount of "pure standard C++ code" would never compile on these platforms.
Then, there is also the reality that most platforms today, even really small embedded systems have an operating system. The vast majority of them are POSIX compliant to some level (except for Windows, but Windows doesn't support any exotic platform anyways). So, in effect, platform-specific code that relies on POSIX functions is not really that bad since it is likely that most exotic platforms have them, for the most part.
I guess what I'm really getting at here is that this pure dividing line that you have in your mind about "pure C++" versus platform-specific code is really just an imaginary one. Every platform (compiler + std-lib + OS + ext-libs) lies somewhere along a continuum of level of support for standard language features, standard library features, OS API functions, and so on. And by that measure, all C++ code is platform-specific.
The only real question is how wide of a net it casts. For example, most Boost libraries (except for recent "flimsy" ones) generally support compilers down to a reasonable level of C++98 support, and many even try to support as far back as early 90s compilers and std-libs.
To know if a library, part of Boost or not, has wide enough support for your intended applications or platforms, you have the define the boundaries of that support. Just saying "pure C++" is not enough, it means nothing in the real world. You cannot say that you will be using C++11 compilers just after you've taken Boost.Thread as an example of a library with platform-specific code. Many C++11 implementations have very flimsy support for std::thread, but others do better, and that issue is as much of a "platform-specific" issue as using Boost.Thread will ever be.
The only real way to ever be sure about your platform support envelope is to actual set up machines (e.g., virtual machines, emulators, or real hardware) that will provide representative worst-cases. You have to select those worst-case machines based on a realistic assessment of what your clients may be using, and you have to keep that assessment up to date. You can create a regression test suite for your particular project, that uses the particular (Boost) libraries, and test that suite on all your worst-case test environments. Whatever doesn't pass the test, doesn't pass the test, it's that simple. And yes, you might find out in the future that some Boost library won't work under some new exotic platform, and if that happens you need to either get the Boost dev-team to add code to support it, or you have to re-write your code to get around it, but that's what software maintenance is all about, and it's a cost you have to anticipate, and such problems will come not only from Boost, but from the OS and from the compiler vendors too! At least, with Boost, you can fix the code yourself and contribute it to Boost, which you can't always do with OS or compiler vendors.
We had "Boost or not" discussion too. We decided not to use it.
We had some untypical hardware platforms to serve with one source code. Especially running boost on AVR was simply impossible because RTTI and exceptions, which Boost requires for a lot of things, aren't available.
There are parts of boost which use compiler specific "hacks" to e.g. get information about class structure.
We tried splitting the packages, but the inter dependency is quite high (at least 3 or 4 years ago).
In the meantime, C++11 was underway and GCC started supporting more and more. With that many reasons to use from boost faded (Which Boost features overlap with C++11?). We implemented the rest of our needs from scratch (with relative low effort thanks to variadic templates and other TMP features in C++11).
After a steep learning curve we have all we need without external libraries.
At the same time we have pondered the future of Boost. We expected the newly standardized C++11 features would be removed from boost. I don't know the current roadmap for Boost, but at the time our uncertainty made us vote against Boost.
This is not a real answer to your question, but it may help you decide whether to use Boost. (And sorry, it was to large for a comment)
Related
I work on large scale, multi platform, real time networked applications. The projects I work on lack any real use of containers or the Standard Library in general, no smart pointers or really any "modern" C++ language features. Lots of raw dynamically allocated arrays are common place.
I would very much like to start using the Standard Library and some of the C++11 spec, however, there are many people also working on my projects that are against because "STL / C++11 isn't as portable, we take a risk using it". We do run software on a wide variety of embedded systems as well as fully fledged Ubuntu/Windows/Mac OS systems.
So, to my question; what are the actual issues of portability with concern to the Standard Library and C++11? Is it just a case of having g++ past a certain version? Are there some platforms that have no support? Are compiled libraries required and if so, are they difficult to obtain/compile? Has anyone had serious issues being burnt by non-portable pure C++?
Library support for the new C++11 Standard is pretty complete for either Visual C++ 2012, gcc >= 4.7 and Clang >= 3.1, apart from some concurrency stuff. Compiler support for all the individual language features is another matter. See this link for an up to date overview of supported C++11 features.
For an in-depth analysis of C++ in an embedded/real-time environment, Scott Meyers's presentation materials are really great. It discusses costs of virtual functions, exception handling and templates, and much more. In particular, you might want to look at his analysis of C++ features such as heap allocations, runtime type information and exceptions, which have indeterminate worst-case timing guarantees, which matter for real-time systems.
It's those kind of issues and not portability that should be your major concern (if you care about your granny's pacemaker...)
Any compiler for C++ should support some version of the standard library. The standard library is part of C++. Not supporting it means the compiler is not a C++ compiler. I would be very surprised if any of the compilers you're using at the moment don't portably support the C++03 standard library, so there's no excuse there. Of course, the compiler will have to be have been updated since 2003, but unless you're compiling for some archaic system that is only supported by an archaic compiler, you'll have no problems.
As for C++11, support is pretty good at the moment. Both GCC and MSVC have a large portion of the C++11 standard library supported already. Again, if you're using the latest versions of these compilers and they support the systems you want to compile for, then there's no reason you can't use the subset of the C++11 standard library that they support - which is almost all of it.
C++ without the standard library just isn't C++. The language and library features go hand in hand.
There are lists of supported C++11 library features for GCC's libstdc++ and MSVC 2012. I can't find anything similar for LLVM's libc++, but they do have a clang c++11 support page.
The people you are talking to are confusing several different
issues. C++11 isn't really portable today. I don't think any
compiler supports it 100% (although I could be wrong); you can
get away with using large parts of it if (and only if) you limit
yourself to the most recent compilers on two or three platforms
(Windows and Linux, and probably Apple). While these are the
most visible platforms, they represent but a small part of all
machines. (If you're working on large scale networked
applications, Solaris will probably be important, and Sun CC.
Unless Sun have greatly changed since I last worked on it, that
means that there are even parts of C++03 that you can't count
on.)
The STL is a completely different issue. It depends partially
on what you mean by the STL, but there is certainly no
portability problem today in using std::vector. locale
might be problematic on a very few compilers (it was with Sun
CC—with both the Rogue Wave and the Stlport libraries),
and some of the algorithms, but for the most part, you can
pretty much count on all of C++03.
And in the end, what are the alternatives? If you don't have
std::vector, you end up implementing something pretty much
like it. If you're really worried about the presence of
std::vector, wrap it in your own class—if ever it's not
available (highly unlikely, unless you go back with a time
machine), just reimplement it, exactly like we did in the
pre-standard days.
Use STLPort with your existing compiler, if it supports it. This is no more than a library of code, and you use other libraries without problem, right?
Every permitted implementation-defined behaviour is listed in publicly available standard draft. There is next to nothing less portable in C+11 than in C++98.
In C++, if I write a simple game like pong using Linux, can that same code be compiled on Windows and OSX? Where can I tell it won't be able to be compiled?
You have three major portability hurdles.
The first, and simplest, is writing C++ code that all the target compilers understand. Note: this is different from writing to the C++ standard. The problem with "writing to the standard" starts with: which standard? You have C++98, C++03, C++TR1 or C++11 or C++14 or C++17? These are all revisions to C++ and the newer one you use the less compliant compilers are likely to be. C++ is very large, and realistically the best you can hope for is C++98 with some C++03 features.
Compilers all add their own extensions, and it's all too easy to unknowingly use them. You would be wise to write to the standard and not to the compiler documentation. Some compilers have a "strict" mode where they will turn off all extensions. You would be wise to do primary development in the compiler which has the most strictures and the best standard compliance. gcc has the -Wstrict family of flags to turn on strict warnings. -ansi will remove extensions which conflict with the standard. -std=c++98 will tell the compiler to work against the C++98 standard and remove GNU C++ extensions.
With that in mind, to remain sane you must restrict yourself to a handful of compilers and only their recent versions. Even writing a relatively simple C library for multiple compilers is difficult. Fortunately, both Linux and OS X use gcc. Windows has Visual C++, but different versions are more like a squabbling family than a single compiler when it comes to compatibility (with the standard or each other), so you'll have to pick a version or two to support. Alternatively, you can use one of the gcc derived compiler environments such as MinGW. Check the [list of C++ compilers](less compliant compilers are likely to be) for compatibility information, but keep in mind this is only for the latest version.
Next is your graphics and sound library. It has to not just be cross platform, it has to look good and be fast on all platforms. These days there's a lot of possibilities, Simple DirectMedia Layer is one. You'll have to choose at what level you want to code. Do you want detailed control? Or do you want an engine to take care of things? There's an existing answer for this so I won't go into details. Be sure to choose one that is dedicated to being cross platform, not just happens to work. Compatibility bugs in your graphics library can sink your project fast.
Finally, there's the simple incompatibilities which exist between the operating systems. POSIX compliance has come a long way, and you're lucky that both Linux and OS X are Unix under the hood, but Windows will always be the odd man out. Things which are likely to bite you mostly have to do with the filesystem. Here's a handful:
Filesystem layout
File path syntax (ie. C:\foo\bar vs /foo/bar)
Mandatory Windows file locking
Differing file permissions systems
Differing models of interprocess communication (ie. fork, shared memory, etc...)
Differing threading models (your graphics library should smooth this out)
There you have it. What a mess, huh? Cross-platform programming is as much a state of mind and statement of purpose as it is a technique. It requires some dedication and extra time. There are some things you can do to make the process less grueling...
Turn on all strictures and warnings and fix them
Turn off all language extensions
Periodically compile and test in Windows, not just at the end
Get programmer who likes Windows on the project
Restrict yourself to as few compilers as you can
Choose a well maintained, well supported graphics library
Isolate platform specific code (for example, in a subclass)
Treat Windows as a first class citizen
The most important thing is to do this all from the start. Portability is not something you bolt on at the end. Not just your code, but your whole design can become unportable if you're not vigilant.
C++ is ultra portable and has compilers available on more platforms than you can shake a stick at. Languages like Java are typically touted as being massively cross platform, ironically they are in fact usually implemented in C++, or C.
That covers "portability". If you actually mean, how cross platform is C++, then not so much: The C++ standard only defines an IO library suitable for console IO - i.e. text based, so as soon as you want develop some kind of GUI, you are going to need to use a GUI framework - and GUI frameworks are historically very platform specific. Windows has multiple "native" GUI frameworks now - the C++ framework made available from Microsoft is still MFC - which wraps the native Win32 API which is a C API. (WPF and WinForms are available to CLR C++).
The Apple Mac's GUI framework is called Cocoa, and is an objective-C library, but its easy to access Objective C from C++ in that development environment.
On Linux there is the GTK+ and Qt frameworks that are both actually ported to Windows and Apple, so one of these C++ frameworks can solve your "how to write a GUI application in C++ once that builds and runs on windows, apple mac and linux".
Of course, its difficult to regard Qt as strictly C++ anymore - Qt defines a special markup for signals and slots that requires a pre-compile compile step.
You can read the standard - if a program respects the standard, it should be compilable on all platforms that have a C++ standard-compliant compiler.
As for 3rd party libraries you might be using, the platform availability is usually specified in the documentation.
When GUI comes to question, there are cross-platform options (such as QT), but you should probably ask yourself - do I really want portability when it comes to UI? Sometimes, it's better to have the GUI part platform-specific.
If you are thinking of porting from Linux to Windows, using OPENGL for the graphical part gives you freedom to run your program on both operating systems as long as you don't use any system specific functionality.
Compared to C, C++ portability is extremely limited, if not completely unexisting. For one you can't disable exceptions (well you can), for the standard specifically says that's undefined behaviour. Many devices don't even support exceptions. So as for that, C++ is ZERO portable. Plus seeing the UB, it's obvioulsy a no-go for zero-fail high-performance real time systems in which exceptions are taboo - undefined behaviour has no place in zero-fail environment. Then there's the name mangling which most, if not every, compiler does completely different. For good portability and inter-compatibility extern "C" would have to be used to export symbols, yet this renders any and all namespace information completely void, resulting in duplicate symbols. One can ofcourse choose to not use namespaces and use unique symbol names. Yet another C++ feature rendered void. Then there's the complexity of the language, which results in implementation difficulties in the various compilers for various architectures. Due to these difficulties, true portability becomes a problem. One can solve this by having a large chain of compiler directives/#ifdefs/macros. Templates? Not even supported by most compilers.
What portability? You mean the semi-portability between a couple of main-stream build targets like MSVC for Windows and GCC for Linux? Even there, in that MAIN-STREAM segment, all the above problems and limitations exist. It's retarded to even think C++ is portable.
Many utilities of boost have been included as part of extended C++ TR1 currently.
Is the complete boost library going to be included once the standard is officially out ? In other words, do I need boost library, if I have complete standard conforming C++11 compiler ?
If not then any reason for that (Reliability cannot be an issue; as far as I know it's written by many people from standard committee) ?
Boost is huge, and of generally high but still varying quality. A lot of the APIs - even the techniques and functionality - are quite "experimental" in the sense that they're still regularly modified as real-world feedback comes in. By way of contrast, the Standard is expected to get it right and need minimal revision, especially when that breaks backwards compatibility.
The standard for review for Standard libraries is much higher than boost's, which is not to say that many boost libraries wouldn't meet the bar - just that many wouldn't too, and that the review process itself is time consuming. There are terrific programmers coordinating and contributing to boost, but they naturally focus their time on their own development interests and things they see as more relevant, so if something is a little specialised, doesn't appeal to their coding style, etc. it may not receive the same scrutiny. The Standard library needs to be scrutinised much more thoroughly as the consequences of change are so much more painful.
While portability is a factor in acceptance of a library into boost, it's not a hard and fast requirement, where-as compiler vendors are expected to make the Standard library run on all C++ compilers, so taking boost more or less as-is and expecting the functionality to be universal on Standard-compliant compiler vendors would put a huge workload on those vendors.
No, in fact very few parts of Boost are "included" in the C++0x revisions to the C++ Standard Library. The parts that are "included" are some of the most commonly used parts of Boost, though.
Really, "included" isn't correct anyway: there are many differences between the Boost libraries and the corresponding additions to the C++ Standard Library. Further, the Boost libraries continue to grow and evolve; the C++0x Standard Library is now finished.
No, Boost is not going to be included in its entirety in C++0x.
Parts of Boost will be, like boost::shared_ptr, Boost.Array, and a couple of other things. But most of Boost is not being included.
How to make sure that my program will be fully portable?
Continuous integration on all target platforms.
1. Test
This is a necessary but not a sufficient condition for doing anything properly. To test portability, you'll want multiple platforms and compilers.
2. Write to the standard, not to your development platform.
This means, only do something if the standard says you can do it. Only expect a particular result if the standard says you can expect it. Only use a library or API if the standard says it exists. The standard is available here (among other places):
http://openassist.googlecode.com/files/C%2B%2B%20Standard%20-%20ANSI%20ISO%20IEC%2014882%202003.pdf
It helps if you assume that:
CHAR_BIT is equal to 9.
sizeof(int) is equal to 5 and int is a 37 bit type. Or a 16 bit type.
the basic character set is EBCDIC.
The epoc began in 1721.
time_t is double
And so on. By which I don't mean, write code that relies on those things to be true, I mean write code that will work if they are, and will also work on a sane implementation.
3. Use the most restrictive and pedantic compiler options you can find,
This is the only practical way to give yourself a reasonable chance of achieving (1).
4. Understand that "real compilers" fail to implement the standard correctly or fully, and make some concessions to this fact.
Theoretically, there's nothing non-portable about a C++ program that uses export. If it's a perfectly good C++ program in every other respect, then it will work on any conforming C++ compiler. But hardly anyone uses a conforming C++ compiler, so there's a de facto common subset of C++ that you'll want to stick to.
5. Understand that the C++ standard provides quite a restricted programming environment
Certain things are not portable in standard C++, such as drawing graphics on a screen, since standard C++ has no graphics or GUI API. So there is no such thing as a "fully portable" GUI program written in C++. So you may or may not need to revise your goal, depending what your program is supposed to do.
If your program requires something that simply cannot be done entirely within standard C++, then you can make your program easier to port by encapsulating that behaviour within an interface which you think should be implementable on all platforms you care about. Then set about implementing it for each one. This doesn't result in a "fully portable" program, though, since to me that means a program which you can compile and run unchanged on any conforming C++ implementation. A program which can be ported to most platforms with a C++ compiler, probably, assuming they have a screen and a mouse, with some bespoke programming work, isn't the same thing.
All this can be taken too far, of course. You will probably actually want to assume that CHAR_BIT is 8 (reading files is madness otherwise), and perhaps even rely on a GUI framework like Qt. But you did say, "fully portable", and one of the main things you need to do to write portable programs is usually to work out how far you're willing to compromise on "fully".
6. Assert what you assume
At compile-time if you can, or runtime otherwise, ensure that if your program requires int to be at least 32 bits (or whatever), then it will fail noisily when it isn't. OK, so comprehensive test coverage would catch cases where your arithmetic silently overflows and gives the wrong answer, but it's hard to write truly comprehensive tests, and anyway the tests might make the same non-portable errors as the code, or some poor sucker who has downloaded your code might not run them all properly.
When you use libraries, you are effectively doing this automatically. You'll #include some header, and if the library isn't available that will fail immediately. At least, you hope it will - it's conceivable that some other implementation could have a header of the same name which does something radically or subtly different. Radical differences usually result in compilation failures, for subtle differences you can test for preprocessor symbols to identify implementations.
Your question:
How to make sure that my program will be fully portable?
cannot be answered satisfyingly. You cannot, in any real-world application, make sure it's portable. You can only prove your expectation by accurate tests of the application on the target platform, as has been already proposed here by Lou Franco.
In the process of developing and testing in parallel on different platforms or environments, every one of us finds his bag of tricks and explores his share of pitfalls. You said in one comment you work on a Windows system. This is fine. Try to get your program working with the Visual Studio compiler (and environment). Then, install CygWin with the GCC 4.x compiler suite. Install the Netbeans IDE & C++ Environment and create a project based on the same sources. Netbeans will use the Cygwin GCC 4.x. If your compiled program works with both toolchains, you mastered probably about 90% of the real-world portability hurdles.
Regards
rbo
Avoid platform-specific libraries.
Make it standards compliant. At least a common subset of the standard that is implemented by vendors on all platforms you intend to deploy your application on.
Factor out platform specific portions from platform-independent ones. Typically, the lowest layer or two should deal with the platform.
Keep abreast with changes of:
Platform/OS APIs
Tool chains
Language features
Test, Deploy. Rinse and repeat.
Unit test it, on each platform, during development
Avoid using platform specific libraries. If you can implement desired functionality using the STL and BOOST only, go ahead.
Develop on the most restrictive compilation environment. Use the smallest set of features from C++. Split the platform-dependent portions of code into separate files. Develop a configuration (make) environment for each platform, as part of the software package.
Making sure to only use libraries that actually exist on all target platforms would be a good start.
It is impossible. What happens when I write my operating system that has a weird C compiler?
That said, to be portable, you need to:
Avoid Win32
Avoid POSIX (which is annoying... You may want to just use Cygwin to provide Windows support)
Avoid any platform specific library. This usually limits you in graphics to wxWindows, GTK, and QT.
TEST. Make sure it works.
Don't assume anything. Windows is weird and uses \r\n, so be careful about that.
I think Visual C++ on windows gives you warnings about "unsafe c functions" and asks you to use the "safe ones", which are not standard. Don't fall for Microsoft's attempt to monopolize your program.
Some things will help:
Autoconf will allow any decent system (ie one that includes a shell) to detect common portability issues and set up the correct headers
Cmake can do this as well, but only on platforms that Cmake itself is available on
Know the platforms that you intend to ship for. If some platform convention contradicts the standard, ignore the standard. I'm serious about that. For example, if you use the standard std::ifstream constructor, which takes a char* argument, you won't be able to open any files with Unicode filenames on Windows—you must use the nonstandard wchar_t* overload there. The functionality lost by not being able to open files that are allowed and legal on the platform severely outweighs the portability gained by using only what the standard knows; in the end, it's the functionality that matters, not the adherence to a particular standard.
This is less a direct answer to the question, than an answer in the light of other answers.
You need to balance a requirement for absolute portability against the expectations of platform users - there are different basic HCI/HIG guidelines for Windows, OS X, KDE and Gnome, and none of the portable GUI toolkits will automatically produce the right results in each (some allow you to apply different layouts, which is a start).
The inbetween approach is to have a pure portable core with multiple native GUIs.
It's not necessary (there is a lot of software that succeeds despite ignoring conventions) but it is a trade-off that needs to be considered - in particular if there is an existing strong native application.
I'm in the process of developing a software library to be used for embedded systems like an ARM chip or a TI DSP (for mostly embedded systems, but it would also be nice if it could also be used in a PC environment). Obviously this is a pretty broad range of target systems, so being able to easily port to different systems is a priority.The library will be used for interfacing with a specific hardware and running some algorithms.
I am thinking C++ is the best option, over C, because it is much easier to maintain and read. I think the additional overhead is worth it for being able to work in the object oriented paradigm. If I was writing for a very specific system, I would work in C but this is not the case.
I'm assuming that these days most compilers for popular embedded systems can handle C++. Is this correct?
Is there any other factors I should consider? Is my line of thinking correct?
If portability is very important for you, especially on an embedded system, then C is certainly a better option than C++. While C++ compilers on embedded platforms are catching up, there's simply no match for the widespread use of C, for which any self-respecting platform has a compliant compiler.
Moreover, I don't think C is inferior to C++ where it comes to interfacing hardware. The amount of abstraction is sufficiently low (i.e. no deep class hierarchies) to make C just as good an option.
There is certainly good support of C++ for ARM. ARM have their own compiler and g++ can also generate EABI compliant ARM code. When it comes to the DSPs, you will have to look at their toolchain to decide what you are going to do. Be aware that the library that comes with a DSP may well not implement the full C or C++ standard library.
C++ is suitable for low-level embedded development and is used in the SymbianOS Kernel. Having said that, you should keep things as simple as possible.
Avoid exceptions which may demand more library support than what is present (therefore use new (std::nothrow) Foo instead of new Foo).
Avoid memory allocations as much as possible and do them as early as possible.
Avoid complex patterns.
Be aware that templates can bloat your code.
I have seen many complaints that C++ is "bloated" and inappropriate for embedded systems.
However, in an interview with Stroustrup and Sutter, Bjarne Stroustrup mentioned that he'd seen heavily templated C++ code going into (IIRC) the braking systems of BMWs, as well as in missile guidance systems for fighter aircraft.
What I take away from this is that experts of the language can generate sophisticated, efficient code in C++ that is most certainly suitable for embedded systems. However, a "C With Classes"[1] programmer that does not know the language inside out will generate bloated code that is inappropriate.
The question boils down to, as always: in which language can your team deliver the best product?
[1] I know that sounds somewhat derogatory, but let me say that I know an awful lot of these guys, and they churn out an awful lot of relatively simple code that gets the job done.
C++ compilers for embedded platforms are much closer to 83's C with classes than 98's C++ standard, let alone C++0x. For instance, some platform we use still compile with a special version of gcc made from gcc-2.95!
This means that your library interface will not be able to provide interfaces with containers/iterators, streams, or such advanced C++ features. You'll have to stick with simple C++ classes, that can very easily be expressed as a C interface with a pointer to a structure as first parameter.
This also means that within your library, you won't be able to use templates to their full power. If you want portability, you will still be restricted to generic containers use of templates, which is, I'm sure you'll admit, only a very tiny part of C++ templates power.
C++ has little or no overhead compared to C if used properly in an embedded environment. C++ has many advantages for information hiding, OO, etc. If your embedded processor is supported by gcc in C then chances are it will also be supported with C++.
On the PC, C++ isn't a problem at all -- high quality compilers are extremely widespread and almost every C compiler is directly associated with a C++ compiler that's quite good, though there are a few exceptions such as lcc and the newly revived pcc.
Larger embedded systems like those based on the ARM are generally quite similar to desktop systems in terms of tool chain availability. In fact, many of the same tools available for desktop machines can also generate code to run on ARM-based machines (e.g., lots of them use ports of gcc/g++). There's less variety for TI DSPs (and a greater emphasis on quality of generated code than source code features), but there are still at least a couple of respectable C++ compilers available.
If you want to work with smaller embedded systems, the situation changes in a hurry. If you want to be able to target something like a PIC or an AVR, C++ isn't really much of an option. In theory, you could get (for example) Comeau to produce a custom port that generated code you could compile on that target's C compiler -- but chances are pretty good that even if you did, it wouldn't work out very well. These systems are really just too limitated (especially on memory size) for C++ to fit them well.
Depending on what your intended use is for the library, I think I'd suggest implementing it first as C - but the design should keep in mind how it would be incorporated into a C++ design. Then implement C++ classes on top of and/or along side of the C implementation (there's no reason this step cannot be done concurrently with the first). If your C design is done with a C++ design in mind, it's likely to be as clean, readable and maintainable as the C++ design would be. This is somewhat more work, but I think you'll end up with a library that's useful in more situations.
While you'll find C++ used more and more on various embedded projects, there are still many that restrict themselves to C (and I'd guess this is more often the case than not) - regardless of whether or not the tools support C++. It would be a shame to have a nice library of routines that you could bring to a new project you're working on, but be unable to use them because C++ isn't being used on that particular project.
In general, it's much easier to use a well-designed C library from C++ than the other way around. I've taken this approach with several sets of code including parsing Intel Hex files, a simple command parser, manipulating synchronization objects, FSM frameworks, etc. I'm planning on doing a simple XML parser at some point.
Here's an entirely different C++-vs-C argument: stable ABIs. If your library exports a C ABI, it can be compiled with any compiler that works on the system, because C ABIs are generally platform standards. If your library exports a C++ ABI, it can only be compiled with a matching compiler -- because C++ ABIs are usually not platform standards, and often differ from compiler to compiler and even version to version.
Interestingly, one of the rare exceptions to this is ARM; there's an ARM C++ ABI specification, and all compliant ARM compilers follow it. This is not true on x86; on x86, you're lucky if a C++ library compiled with a 4.1 version of GCC will link correctly with an application compiled with GCC 4.4, and don't even ask about 3.4.6.
Even if you export a C ABI, you can have problems. If your library uses C++ internally, it will then link to libstdc++ for things in the C++ std:: namespace. If your user compiles a C++ application that uses your library, they'll also link to libstdc++ -- and so the overall application gets linked to libstdc++ twice, and their libstdc++ may not be compatible with your libstdc++, which can (or so I understand) lead to odd errors from the intersection of the two. Considerably less likely, but still possible.
All of these arguments only apply because you're writing a library, and they're not showstoppers. But they are things to be aware of.