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I'm having a debate with a friend and we're wondering why so many open source projects have decided to go with C instead of C++. Projects such as Apache, GTK, Gnome and more opted for C, but why not C++ since it's almost the same?
We're precisely looking for the reasons that would have led those projects (not only those I've listed but all C projects) to go with C instead of C++. Topics can be performance, ease of programming, debugging, testing, conception, etc.
C is very portable, much more than C++ was 10 years ago.
Also, C is very entrenched in the Unix tradition. Read more in 'The Art of Unix Programming', about Unix and OO in general, and about specific languages on unix (including C and C++).
There are numerous counter examples: everything based on Qt for one.
Also, on my Debian testing system:
edd#ron:~$ apt-cache rdepends libstdc++6|wc -l
4101
So that's 4101 packages depending on the basic C++ library. For comparison, I get about 14,982 for libc6 or roughly 3.6 as many. But it is not if there aren't any C++ projects in Open Source land.
Edit: Thinko on my part: as the C++ packages also depend on libc6, the ratio really is
(14982 - 4101)/4101 = 2.65
so there are roughly 2 1/2 times as many packages implemented in C than there are in C++.
Eric Raymond's wonderful book "The Art of Unix Programming" has some reflections on this issue (the whole book is well worth reading in either the paper or free online editions, I'm just pointing to the relevant section -- Eric was involved with the coining and introduction of the term "open source", and is always well worth reading;-0).
Summarizing that section, Raymond claims that "OO languages show some tendency to suck programmers into the trap of excessive layering" and Unix programmers (and by extension open-source programmers) resist that trap of "thick glue".
Later in the book, you find some considerations specifically about C++, such as "It may be that C++'s realization of OO is particularly problem-prone". Whether you agree or not, the whole text is well worth reading (I can hardly do it justice here!-), and rich with bibliography pointing you to many other relevant studies and publications.
Linus Torvalds has ranted several times on the topic of C++ -- he uses C for git, and of course the Linux kernel is mostly C:
on C++ and git (warning: don flame-retardant first)
an interview with Linus from 1998
You can easily find more of these, and while it's in his nature to get a bit flamey about these things, there are some valid points.
One of the more interesting (from where I'm sitting, anyway) is the observation that C++ compilers and libraries were (and to some degree are) a lot more buggy than the corresponding C compilers. This stands to reason given the relative complexities of the two languages.
It smells a little of "not invented here" (NIH) syndrome, but when you have the entire Linux kernel developer base, you can sometimes afford to reinvent things "The Right Way".
A lot of the projects started before C++ was standardized, so C was the obvious choice and a change later would be hard. C was standardized about a decade before C++, and has been more nearly portable for even longer. So, it was largely a pragmatic decision at the time, inspired in part by the Unix heritage of using C for most code.
C++ is a mess. It is overly complicated language, so complicated that only few people can say that they know all the bits. And fewer compilers which really complies to C++ standard.
So I think the reason is simplicity and portability.
If you want higher-level and object-oriented programming, then I think C++ is just competed with others like Python. (Note that I programmed in C++ few years, it's fast and has some features from higher-level languages that speeds up development, no offence.)
I have worked on a few C++ projects in my time, all of which have ended in tears one way or the other. At the most fundamental level, the truth is that people can't be trusted. They can't be trusted to write good code, they can't be trusted to debug it, and they certainly can't be trusted to understand it when they have to come back and modify it again weeks/months later.
C code doesn't have a lot of the weird stuff in C++ that makes it hard to debug (constructors/destructors, anything that happens with static global objects during cpp_initialize() time, etc.). That just makes it easier to deal with when developing and maintaining a big project.
Maybe I'm a luddite, but every time someone says "C++" around me I get shivers.
Some people have mentioned portability, but in this day, the portability of C++ isn't much of an issue (it runs on anything GCC runs on, which is essentially anything). However, portability is more than just architecture-to-architecture or OS-to-OS. In the case of C++, it includes compiler-to-compiler.
Let's discuss ABI, or Application Binary Interface. This basically means "how your code translates into assembly." In C, when you write:
int dostuff(const char *src, char *dest);
You know that you're making a symbol in your object file called _dostuff (C global names are all prefixed by an underscore in the resultant assembly). But in C++, when you write this:
int dostuff(const char *src, char *dest);
int dostuff(const char *src, char *dest, size_t len);
Or even:
int dostuff(std::string src, std::string dest);
All bets are instantly off. You now have two distinct functions, and the compiler has to make each, and has to give each a unique name. So C++ allows (where I believe C doesn't) name mangling, which means those two functions might get translated to _dostuff_cp_cp and _dostuff_cp_cp_s (so that each version of the function that takes a different number of arguments has a different name).
The problem with this is (and I consider this a huge mistake, even though it's not the only problem with cross-compiler portability in C++) that the C++ standard left the details of how to mangle these names up to the compiler. So while one C++ compiler may do that, another may do _cp_cp_s_dostuff, and yet another may do _dostuff_my_compiler_is_teh_coolest_char_ptr_char_ptr_size_t. The problem is exacerbated (always find a way to sneak this word into anything you say or write) by the fact that you have to mangle names for more than just overloaded functions - what about methods and namespaces and method overloading and operator overloading and... (the list goes on). There is only one standard way to ensure that your function's name is actually what you expect it to be in C++:
extern "C" int dostuff(const char *src, char *dest);
Many applications need to have (or at least find it very useful to have) a standard ABI provided by C. Apache, for example, couldn't be nearly as cross-platform and easily extensible if it was in C++ - you'd have to account for the name mangling of a particular compiler (and a particular compiler version - GCC has changed a few times in its history) or require that everyone use the same compiler universally - which means that, every time you upgrade your C++ compiler with a backwards incompatible name-mangling scheme, you have to recompile all your C++ programs.
This post turned into something of a monster, but I think it illustrates a good point, and I'm too tired to try to trim it down.
As someone who dislikes C++ and would pick C over it any day, I can at least give you my impressions on the topic. C++ has several attributes that make it unappealing:
Complicated objects. C++ has tons of ability to speed up OO, which makes the language very complex.
Nonstandard syntax. Even today most C++ compilers support quirks that make ensuring successful and correct compilation between compilers difficult.
Nonstandard libraries. Compared to C libraries, C++ libraries are not nearly as standardized across systems. Having had to deal with Make issues associated with this before I can tell you that going with C is a big time saver.
That said, C++ does have the benefits of supporting objects. But when it comes down to it, even for large projects, modularity can be accomplished without objects. When you add in the fact that essentially every programmer who might contribute code to any project can program C, it seems hard to make the choice to go with anything else if you need to write your code that close to the metal.
All that said, many projects jump over C++ and go to languages like Python, Java, or Ruby because they provide more abstraction and faster development. When you add in their ability to support compiling out to/loading in from C code for parts that need the performance kick, C++ loses what edge it could have had.
If you look at recent open source projects, you'll see many of them use C++. KDE, for instance, has all of its subprojects in C++. But for projects that started a decade ago, it was a risky decision. C was way more standardized at the time, both formally and in practice (compiler implementations). Also C++ depends on a bigger runtime and lacked good libraries at that time. You know that personal preference plays a big role in such decision, and at that time the C workforce in UNIX/Linux projects was far bigger than C++, so the probability that the initial developer(s) for a new project were more comfortable with C was greater. Also, any project that needs to expose an API would do that in C (to avoid ABI problems), so that would be another argument to favor C.
And finally, before smart pointers became popular, it was much more dangerous to program in C++. You'd need more skilled programmers, and they would need to be overly cautions. Although C has the same problems, its simpler data structures are easier to debug using bounds checking tools/libraries.
Also consider that C++ is an option only for high-level code (desktop apps and the like). The kernel, drivers, etc. are not viable candidates for C++ development. C++ has too much "under the hood" behavior (constructor/destructor chains, virtual methods table, etc) and in such projects you need to be sure the resulting machine/assembly code won't have any surprises and doesn't depend on runtime library support to work.
One important aspect in addition to others that will doubtless be mentioned is that C is easier to interface with other languages, so in the case of a library intended to be widely useful, C may be chosen even nowadays for this purpose.
To take examples I am familiar with, the toolkit GTK+ (in C) has robust OCaml bindings, while Qt and Cocoa (respectively in C++ and Objective C) only have proof-of-concepts for such bindings. I believe that the difficulty to interface languages other than C with OCaml is part of the reason.
One reason might be that the GNU coding standards specifically ask you to use C. Another reason I can think of is that the free software tools work better with C than C++. For example, GNU indent doesn't do C++ as well as it does C, or etags doesn't parse C++ as well as it parses C.
I can list a couple more reasons
C code produces more compact object
code. Try to compile 'Hello World'
as C and C++ program and compare the
size of the executable. May not be too relevant today but definitely was a factor 10+ years ago
It is much easier to use dynamic
linking with C programs. Most of
the C++ libraries still expose entry
points through C interface. So instead of writing a bridge between C++ and C why not to program the whole thing in C?
First of all, some of the biggest open source projects are written in C++: Open Office, Firefox, Chrome, MySQL,...
Having said that, there are also many big projects written in C. Reasons vary: they may have been started when C++ was not standardized yet, or the authors are/were more comfortable with C, or they hoped that the easier learning curve for C would attract more contributors.
If correctly implemented C is very fast and very portable and the compilers are there
C++ is different for each compiler available, the libraries dont agree, the standards don´t match.
You can read Dov Bulka to find what not to do in cpp, you can read tesseract ocr at Google code, you can read lots of things - most of which depend on where you are to determine which code linguistic is superior. Where did you read that c has more source code up in open source than cpp? Well of course you read that in a c forum. That's where. Go to some other programming linguistic. Do the same search, you will find that that code has more open source.
Related
I about to take some courses in Pattern Recognition.
As i have no prior knowledge in either C or C++, my professors told me to learn a bit of one of them before the course, and learn more when doing the course.
Which one should i pick?
The prior knowledge in programming i have is limited to mostly C# but some PHP, SQL and Prolog as well.
The choice of a low-level language like C or C++ probably means you are into performance at the cost of the development time.
If this is your first low-level language, then learn C. It is simple, robust and proven language, and it allows to write the fast code. It has a decades long record of portability. It is much easier to integrate C code with code written in other languages. With C++ it is too easy to make things wrong. C++ requires much greater degree of language mastery and much more programmer's attention to make things right. While it is possible to write fast code in C++, it's more of an art than doing the same thing in C.
If you have only a few months to learn, then at the end you'll be able to write an OK C code, but this time is simply not enough to get enough experience with C++, hence your C++ code written in the first year or two will be awful.
See, for example, severe criticism of C++ from Linus Torvalds: C++ is a horrible language and C++ productivity. Basically, it boils down to C++ being too complicated even for professional programmers, and C++ code being ambiguous with context-dependent behaviour (this may be considered a higher-level language feature, but it makes more difficult to reason about the performance).
One of the major open source libraries for computer vision, OpenCV, is available both for C and C++, but it is also available for Python, which is a much easier language to get the things done quickly (and also to learn as a first language). BTW, I assume if you manage to offload most of the work to the library, which itself is written in C/C++, the performance cost of Python won't be huge (but generally Python is 10x slower than C).
Stroustrup (inventor of C++) argues that C++ is easier to learn than C:
There will be less type errors to catch manually […] fewer tricks to learn […], and better libraries available.
With that in mind, go for C++.
C and C++ are fundamentally different in the way they approach programming. If you have experience with C#, C++ would be a choice since it is object oriented as well. Also, even though they are different, knowing C++ will let you read (and mostly understand) C code as well. Also, check out this question for some information on the differences between these languages.
I would recommend learning C++ as this probably be easiest if you know about classes etc from C#. Also you can write free functions in C++ but is harder to write classes in C.
A standard library you will likely use is opencv.
C# will set you in good stead to master C/C++. You will probably be able to see through the opencv code examples and understand them.
You can likely get by with enough C you pick up from working through the examples and becoming familiar with them. The focus of the course will be on the algorithms and not how fancy your code is.
Sounds like a fun course! Good luck.
I noticed some not so old VM languages like Lua, NekoVM, and Potion written in C.
It looked like they were reimplementing many C++ features.
Is there a benefit to writing them in C rather than C++?
I know something about Lua.
Lua is written in pure ANSI Standard C and compiles on any ANSI platform with no errors and no warnings. Thus Lua runs on almost any platform in the world, including things like Canon PowerShot cameras. It's a lot harder to get C++ to run on weird little embedded platforms.
Lua is a high-performance VM, and because C cannot express method calls (which might be virtual or might not) and operator overloading, it is much easier to predict the performance of C code just by looking at the code. C++, especially with the template library, makes it a little too easy to burn resources without being aware of it. (A full implementation of Lua including not only VM but libraries fits in 145K of x86 object code. The whole language fits even in a tiny 256K cache, which you find at L2 on Intel i7 and L1 on older chips. Unless you really know what you're doing, it's much harder to write C++ that compiles to something this small.)
These are two good reasons to write a VM in C.
It looked like they were reimplementing many C++ features.
Are you suggesting it's easier to implement polymorphism in C++ rather than C? I think you are greatly mistaken.
If you write a VM in C++, you wouldn't implement polymorphism in terms of C++'s polymorphism. You'd roll your own virtual table which maps function names to pointers, or something like that.
People are used to C. I have to admit that I'm more likely to write C for my own projects, even though I've been writing C++ since cfront 1.0.
If you want complete control over things, C is a little easier.
One obvious answer is interoperability. Any time language X has to call functions defined in language Y, you usually make sure that either X or Y is C (the language C, that is)
C++ doesn't define an ABI, so calling C++ code from another language is a bit tricky to do portably. But calling C code is almost trivial. That means that at least part of your VM is probably going to have to be written in C, and then why not be consistent and write the entire thing in C?
Another advantage of C is that it's simple. Everyone can read it, and there are plenty of programmers to help you write it. C++ is, for good and bad, much more of an experts language. You can do a lot of impressive things in C++, and it can save you a lot of work, but there are also fewer programmers who are really good at it.
It's much harder to be "good" at C++, and until one is good at it they will have a lot of bugs and problems. Now, especially when working on large projects with many people, the chance that one of them won't be good enough is much bigger, so coding the project in C is often less risky. There are also portability issues - C code is much easier to port across compilers than C++.
Lua also has many features that are very easy to implement in Lisp, so why doesn't it take that as a basis? The point is that C is little more than glorified assembler code with only a thin layer of abstraction. It is like a somewhat polished blank slate, on which you can build your higher level abstractions. C++ is such a building. Lua is a different building, and if it had to use C++ abstractions, it would have to bend its intent around the existing C++ structure. Starting from the blank slate instead gives you the freedom to build it like you want.
In many cases, code in C could be much faster than C++. For instance most of the functions in the stdio.c library are faster than iostream. scanf is faster than cin, printf is faster than cout etc.
and VMs demand high performance, so C code makes perfect sense, although the programs would most probably take longer to develop.
C++ is implemented in C. I suspect everyone was following the C++ approach.
Even though modern C++ compilers skip (or conceal) the explicit C++ to C translation as a discrete step, the C++ language has peculiarities that stem from the underlying C implementation.
Two examples.
Pointers in addition to references is entirely because of C. References are sufficient, and that's the way Java, Python and Ruby all work.
The classes are not first-class objects that exist at run-time because the class is only a way to define the attributes and method functions in the underlying C code. Class objects exist at run-time in Java, Python and Ruby, and can be manipulated.
Just a side note, you should look into CLR (Rotor-incarnation) and Java sources and you will note it is far more C++-as-C rather than modern or good C++. So it has a parallel there and it is a side-effect of abstracting for toys and making it average-performance happy for the crowd in managed languages.
It also helps avoid pitfalls of naive C++ usage. Exceptions and all other sort of things (bits David at boost consulting kicked off and more while we build sequencers and audio sampling before he even had a job :) are an issue too..
Python integration is another matter, and has a messy history in boost for example.. But for primitive data types and interfaces/interop and machine abstraction, well it is quite clear nothing beats C. No compiler issues either, and it still bootstraps many things before you get to anything as influential as it is/was/will be.
Stepanov recognised this achievement when he nailed STL, and Bjarne nailed it with templates.. Those are the three things always worth thinking about, as you don't have a decent incarnation of them in popular managed languages, not to that expressivness and power. All of that more than 20 years later, which is remarkable and all still bootstrap via C/C++.. Legacy of goodness (but I'm not defending 'dark age' C code c1982-2000, just the idea, yuo can misuse anything ).
I got a comment to an answer I posted on a C question, where the commenter suggested the code should be written to compile with a C++ compiler, since the original question mentioned the code should be "portable".
Is this a common interpretation of "portable C"? As I said in a further comment to that answer, it's totally surprising to me, I consider portability to mean something completely different, and see very little benefit in writing C code that is also legal C++.
The current C++ (1998) standard incorporates the C (1989) standard. Some fine print regarding type safety put aside, that means "good" C89 should compile fine in a C++ compiler.
The problem is that the current C standard is that of 1999 (C99) - which is not yet officially part of the C++ standard (AFAIK)(*). That means that many of the "nicer" features of C99 (long long int, stdint.h, ...), while supported by many C++ compilers, are not strictly compliant.
"Portable" C means something else entirely, and has little to do with official ISO/ANSI standards. It means that your code does not make assumptions on the host environment. (The size of int, endianess, non-standard functions or errno numbers, stuff like that.)
From a coding style guide I once wrote for a cross-platform project:
Cross-Platform DNA (Do Not Assume)
There are no native datatypes. The only datatypes you might use are those declared in the standard library.
char, short, int and long are of different size each, just like float, double, and long double.
int is not 32 bits.
char is neither signed nor unsigned.
char cannot hold a number, only characters.
Casting a short type into a longer one (int -> long) breaks alignment rules of the CPU.
int and int* are of different size.
int* and long* are of different size (as are pointers to any other datatype).
You do remember the native datatypes do not even exist?
'a' - 'A' does not yield the same result as 'z' - 'Z'.
'Z' - 'A' does not yield the same result as 'z' - 'a', and is not equal to 25.
You cannot do anything with a NULL pointer except test its value; dereferencing it will crash the system.
Arithmetics involving both signed and unsigned types do not work.
Alignment rules for datatypes change randomly.
Internal layout of datatypes changes randomly.
Specific behaviour of over- and underflows changes randomly.
Function-call ABIs change randomly.
Operands are evaluated in random order.
Only the compiler can work around this randomness. The randomness will change with the next release of the CPU / OS / compiler.
For pointers, == and != only work for pointers to the exact same datatype.
<, > work only for pointers into the same array. They work only for char's explicitly declared unsigned.
You still remember the native datatypes do not exist?
size_t (the type of the return value of sizeof) can not be cast into any other datatype.
ptrdiff_t (the type of the return value of substracting one pointer from the other) can not be cast into any other datatype.
wchar_t (the type of a "wide" character, the exact nature of which is implementation-defined) can not be cast into any other datatype.
Any ..._t datatype cannot be cast into any other datatype
(*): This was true at the time of writing. Things have changed a bit with C++11, but the gist of my answer holds true.
No. My response Why artificially limit your code to C? has some examples of standards-compliant C99 not compiling as C++; earlier C had fewer differences, but C++ has stronger typing and different treatment of the (void) function argument list.
As to whether there is benefit to making C 'portable' to C++ - the particular project which was referenced in that answer was a virtual machine for a traits based language, so doesn't fit the C++ object model, and has a lot of cases where you are pulling void* of the interpreter's stack and then converting to structs representing the layout of built-in object types. To make the code 'portable' to C++ it would have add a lot of casts, which do nothing for type safety.
Portability means writing your code so that it compiles and has the same behaviour using different compilers and/or different platforms (i.e. relying on behaviour mandated by the ISO standard(s) wherever possible).
Getting it to compile using a different language's compiler is a nice-to-have (perhaps) but I don't think that's what is meant by portability. Since C++ and C are now diverging more and more, this will be harder to achieve.
On the other hand, when writing C code I would still avoid using "class" as an identifier for example.
No, "portable" doesn't mean "compiles on a C++ compiler", it means "compiles on any Standard comformant C compiler" with consistent, defined behavior.
And don't deprive yourself of, say, C99 improvements just to maintain C++ compatibility.
But as long as maintaining compatibility doesn't tie your hands, if you can avoid using "class" and "virtual" and the the like, all the better. If you're writing open source, someone may want to port your code to C++; if you're wring for hire, you company/client may want to port sometime in the future. hey, maybe you'll even want to port it to C++ in the future
Being a "good steward" not leaving rubbish around the campfire, is just good karma in whatever you do.
And please, do try to keep incompatibilities out of your headers. Even if your code is never ported, people may need to link to it from C++, so having a header that doesn't use any C++ reserved words, is cool.
It depends. If you're doing something that might be useful to a C++ user, then it might be a good idea. If you're doing something that C++ users would never need but that C users might find convenient, don't bother making it C++ compliant.
If you're writing a program that does something a lot of people do, you might consider making it as widely-usable as possible. If you're writing an addition to the Linux kernel, you can throw C++ compatability out the window - it'll never be needed.
Try to guess who might use your code, and if you think a lot of C++ fans might find your code useful, consider making it C++ friendly. However, if you don't think most C++ programmers would need it (i.e. it's a feature that is already fairly standardized in C++), don't bother.
It is definitely common practice to compile C code using a C++ compiler in order to do stricter type checking. Though there are C-specific tools to do that like lint, it is more convenient to use a C++ compiler.
Using a C++ compiler to compile C code means that you commonly have to surround your includes with extern "C" blocks to tell the compiler not to mangle function names. However this is not legal C syntax. Effectively you are using C++ syntax and your code which is supposedly C, is actually C++. Also a tendency to use "C++ convenience" starts to creep in like using unnamed unions.
If you need to keep your code strictly C, you need to be careful.
FWIW, once a project gains a certain size and momentum, it is not unlikely that it may actually benefit from C++ compatibility: even if it not going to be ported to C++ directly, there are really many modern tools related to working/processing C++ source code.
In this sense, a lack of compatibility with C++, may actually mean that you may have to come up with your own tools to do specific things. I fully understand the reasoning behind favoring C over C++ for some platforms, environments and projects, but still C++ compatibility generally simplifies project design in the long run, and most importantly: it provides options.
Besides, there are many C projects that eventually become so large that they may actually benefit from C++'s capabilities like for example improved suport for abstraction and encapsulation using classes with access modifiers.
Look at the linux (kernel) or gcc projects for example, both of which are basically "C only", still there are regularly discussions in both developer communities about the potential gains of switching to C++.
And in fact, there's currently an ongoing gcc effort (in the FSF tree!) to port the gcc sources into valid C++ syntax (see: gcc-in-cxx for details), so that a C++ compiler can be used to compile the source code.
This was basically initiated by a long term gcc hacker: Ian Lance Taylor.
Initially, this is only meant to provide for better error checking, as well as improved compatibility (i.e. once this step is completed, it means that you don't necessarily have to have a C compiler to to compile gcc, you could also just use a C++ compiler, if you happen to be 'just' a C++ developer, and that's what you got anyway).
But eventually, this branch is meant to encourage migration towards C++ as the implementation language of gcc, which is a really revolutionary step - a paradigm shift which is being critically perceived by those FSF folks.
On the other hand, it's obvious how severely gcc is already limited by its internal structure, and that anything that at least helps improve this situation, should be applauded: getting started contributing to the gcc project is unnecessarily complicated and tedious, mostly due to the complex internal structure, that's already to started to emulate many of the more high level features in C++ using macros and gcc specific extensions.
Preparing the gcc code base for an eventual switch to C++ is the most logical thing to do (no matter when it's actually done, though!), and it is actually required in order to remain competitive, interesting and plain simply relevant, this applies in particular due to very promising efforts such as llvm, which do not bring all this cruft, complexity with them.
While writing very complex software in C is often course possible, it is made unnecessarily complicated to do so, many projects have plain simply outgrown C a long time ago. This doesn't mean that C isn't relevant anymore, quite the opposite. But given a certain code base and complexity, C simply isn't necessarily the ideal tool for the job.
In fact, you could even argue that C++ isn't necessarily the ideal language for certain projects, but as long as a language natively supports encapsulation and provides means to enforce these abstractions, people can work around these limitations.
Only because it is obviously possible to write very complex software in very low level languages, doesn't mean that we should necessarily do so, or that it really is effective in the first place.
I am talking here about complex software with hundreds of thousands lines of code, with a lifespan of several decades. In such a scenario, options are increasingly important.
No, matter of taste.
I hate to cast void pointers, clutters the code for not much benefit.
char * p = (char *)malloc(100);
vs
char * p = malloc(100);
and when I write an "object oriented" C library module, I really like using the 'this' as my object pointer and as it is a C++ keyword it would not compile in C++ (it's intentional as these kind of modules are pointless in C++ given that they do exist as such in stl and libraries).
Why do you see little benefit? It's pretty easy to do and who knows how you will want to use the code in future.
No, being compilable by C++ is not a common interpretation of portable. Dealing with really old code, K&R style declarations are highly portable but can't be compiled under C++.
As already pointed out, you may wish to use C99 enhancements. However, I'd suggest you consider all your target users and ensure they can make use of the enhancements. Don't just use variable length arrays etc. because you have the freedom to but only if really justified.
Yes it is a good thing to maintain C++ compatibility as much as possible - other people may have a good reason for needing to compile C code as C++. For instance, if they want to include it in an MFC application they would have to build plain C in a separate DLL or library rather than just being able to include your code in a single project.
There's also the argument that running a compiler in C++ mode may pick up subtle bugs, depending on the compiler, if it applies different optimisations.
AFAIK all of the code in classic text The C programming language, Second edition can be compiled using a standard C++ compilers like GCC (g++). If your C code is upto the standards followed in that classic text, then good enough & you're ready to compile your C code using a C++ compiler.
Take the instance of linux kernel source code which is mostly written in C with some inline assembler code, it's a nightmare compiling the linux kernel code with a C++ compiler, because of least possible reason that 'new' is being used as an variable name in linux kernel code, where as C++ doesn't allow the usage of 'new' as a variable name. I am just giving one example here. Remember that linux kernel is portable & compiles & runs very well in intel, ppc, sparc etc architectures. This is just to illustrate that portability does have different meanings in software world. If you want to compile C code using a C++ compiler, you are migrating your code base from C to C++. I see it as two different programming languages for most obvious reason that C programmers doesn't like C++ much. But I like both of them & I use both of them a lot. Your C code is portable, but you should make sure you follow standard techniques to have your C++ code portable while you migrate your C code to C++ code. Read on to see from where you'd get the standard techniques.
You have to be very careful porting the C code to C++ code & the next question that I'd ask is, why would you bother to do that if some piece of C code is portable & running well without any issues? I can't accept managebility, again linux kernel a big code source in C is being managed very well.
Always see the two programming languages C & C++ as different programming languages, though C++ does support C & its basic notion is to always support for that wonderful language for backward compatibility. If you're not looking at these two languages as different tools, then you fall under the land of popular, ugly C/C++ programming language wars & make yourself dirty.
Use the following rules when choosing portability:
a) Does your code (C or C++) need to be compiled on different architectures possibly using native C/C++ compilers?
b) Do a study of C/C++ compilers on the different architectures that you wish to run your program & plan for code porting. Invest good time on this.
c) As far as possible try to provide a clean layer of separation between C code & C++ code. If your C code is portable, you just need to write C++ wrappers around that portable C code again using portable C++ coding techniques.
Turn to some good C++ books on how to write portable C++ code. I personally recommend The C++ programming language by Bjarne Stroustrup himself, Effective C++ series from Scott meyers & popular DDJ articles out there in www.ddj.com.
PS: Linux kernel example in my post is just to illustrate that portability does mean different meanings in software programming & doesn't criticize that linux kernel is written in C & not in C++.
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Although people seem to like to complain about C++, I haven't been able to find much evidence as to why you would want to choose C over C++. C doesn't seem to get nearly as much flak and if C++ has all these problems why can't you just restrict yourself to the C subset? What are your thoughts/experience?
Joel's answer is good for reasons you might have to use C, though there are a few others:
You must meet industry guidelines, which are easier to prove and test for in C
You have tools to work with C, but not C++ (think not just about the compiler, but all the support tools, coverage, analysis, etc)
Your target developers are C gurus
You're writing drivers, kernels, or other low-level code
You know the C++ compiler isn't good at optimizing the kind of code you need to write
Your app not only doesn't lend itself to be object-oriented but would be harder to write in that form
In some cases, though, you might want to use C rather than C++:
You want the performance of assembler without the trouble of coding in assembler (C++ is, in theory, capable of 'perfect' performance, but the compilers aren't as good at seeing optimizations a good C programmer will see)
The software you're writing is trivial, or nearly so - whip out the tiny C compiler, write a few lines of code, compile and you're all set - no need to open a huge editor with helpers, no need to write practically empty and useless classes, deal with namespaces, etc. You can do nearly the same thing with a C++ compiler and simply use the C subset, but the C++ compiler is slower, even for tiny programs.
You need extreme performance or small code size and know the C++ compiler will actually make it harder to accomplish due to the size and performance of the libraries.
You contend that you could just use the C subset and compile with a C++ compiler, but you'll find that if you do that you'll get slightly different results depending on the compiler.
Regardless, if you're doing that, you're using C. Is your question really "Why don't C programmers use C++ compilers?" If it is, then you either don't understand the language differences, or you don't understand the compiler theory.
I like minimalism & simplicity.
Because they already know C
Because they're building an embedded app for a platform that only has a C compiler
Because they're maintaining legacy software written in C
You're writing something on the level of an operating system, a relational database engine, or a retail 3D video game engine.
Fears of performance or bloat are not good reason to forgo C++. Every language has its potential pitfalls and trade offs - good programmers learn about these and where necessary develop coping strategies, poor programmers will fall foul and blame the language.
Interpreted Python is in many ways considered to be a "slow" language, but for non-trivial tasks a skilled Python programmer can easily produce code that executes faster than that of an inexperienced C developer.
In my industry, video games, we write high performance code in C++ by avoiding things such as RTTI, exceptions, or virtual-functions in inner loops. These can be extremely useful but have performance or bloat problems that it's desirable to avoid. If we were to go a step further and switch entirely to C we would gain little and lose the most useful constructs of C++.
The biggest practical reason for preferring C is that support is more widespread than C++. There are many platforms, particularly embedded ones, that do not even have C++ compilers.
There is also the matter of compatibility for vendors. While C has a stable and well-defined ABI (Application Binary Interface) C++ does not. The ABI in C++ is more complicated due to such things as vtables and constructurs/destructors so is implemented differently with every vendor, and even versions of a vendors toolchain.
In real-terms this means you cannot take a library generated by one compiler and link it with code or a library from another which creates a nightmare for distributed projects or middleware providers of binary libraries.
I take the other view: why use C++ instead of C?
The book The C Programming Language (aka: K&R) tells you clearly how to do everything the language can do in under 300 pages. It's a masterpiece of minimalism. No C++ book even comes close.
The obvious counterargument is that the same could be said of most, if not all, modern languages -- they also can't tell you how to do everything in only a few hundred pages. True. So why use C++ instead? Feature richness? Power? If you need something more feature rich or powerful then go with C#, Objective C, Java, or something else like that. Why burden yourself with the complexities of C++? If you need the degree of control C++ grants then I argue to use C. C can do anything and can do it well.
I choose to write in C because I enjoy working with a small, tight language. I like having access to a standard which can be read in a reasonable amount of time (for me -- I'm a very slow reader). Moreover, I use it to write software for embedded systems for which few desirable C++ compilers exist (like some PIC micro-controllers).
In addition to several other points mentioned already:
Less surprise
that is, it is much easier to see what a piece of code will do do exactly . In C++ you need to approach guru level to be able to know exactly what code the compiler generates (try a combination of templates, multiple inheritance, auto generated constructors, virtual functions and mix in a bit of namespace magic and argument dependent lookup).
In many cases this magic is nice, but for example in real-time systems it can really screw up your day.
I'm used to use C++ for my projects. Then I got a job where plain C is used (a 20 year old evolving codebase of an AV software with poor documentation...).
The 3 things I like in C are:
Nothing is implicit: you see what your program exactly does or not does. This makes debugging easier.
The lack of namespaces and overloads can be an advantage: if you want to know where a certain function is called, just grep through the source code directory and it will tell you. No other special tools needed.
I rediscovered the power of the function pointers. Basically they allow you to do all polymorphic stuff you do in C++, but they are even more flexible.
Linus' answer to your question is "Because C++ is a horrible language"
His evidence is anecdotal at best, but he has a point..
Being more of a low level language, you would prefer it to C++..C++ is C with added libraries and compiler support for extra features (both languages have features the other language doesn't, and implement things differently), but if you have the time and experience with C, you can benefit from extra added low level related powers...[Edited](because you get used to doing more work manually rather than benefit from some powers coming from the language/compiler itself)
Adding links:
Why C++ for embedded
Why are you still using C? PDF
I would google for this.. because there are plenty of commentaries on the web already
Because they're writing a plugin and C++ has no standard ABI.
Long compile times can be annoying. With C++ you can have very long compile times (which means, of course, more time for Stack Overflow!).
If you want your code to be understood by virtually any programmer write in C.
I'm surprised no one's mentioned libraries. Lots of languages can link against C libs and call C functions (including C++ with extern "C"). C++ is pretty much the only thing that can use a C++ lib (defined as 'a lib that uses features in C++ that are not in C [such as overloaded functions, virtual methods, overloaded operators, ...], and does not export everything through C compatible interfaces via extern "C"').
Because they want to use features in C99 that don't have equivalents in C++.
However, there aren't as many C99 features that are useful to C++ as people think at first glance. Variable-length arrays? C++ has std::vectors. Support for complex/imaginary numbers? C++ has a templated complex type. Type-generic math functions? C++ overloaded the standard math functions, causing the same result.
Named initializers? Not in C++, but there's a workaround:
struct My_class_params {
int i;
long j;
std::string name;
My_class_params& set_i(int ii)
{
i = ii;
return *this;
}
My_class_params& set_j(long jj)
{
j = jj;
return *this;
}
template <typename STRING>
My_class_params& set_name(STRING&& n)
{
name = std::forward<STRING>(n);
return *this;
}
My_class_params()
{
// set defaults
}
};
class My_class {
My_class_params params;
public:
My_class(const My_class_params& p) : params(p) { }
...
};
This allows you to write things like:
My_class mc(My_class_params().set_i(5).set_name("Me"));
This is pretty shallow but as a busy student I chose C because I thought C++ would take too long to learn. Many professors at my university won't accept assignments in Python and I needed to pick up something quickly.
Because for many programming tasks C is simpler, and good enough. When I'm programming lightweight utilities especially, I can feel like C++ wants me to build in an elegant supersructure for its own sake, rather than simply write the code.
OTOH, for more complex projects, the elegance provides more good solid structural rigor than would naturally flow out of my keyboard.
Most of the significant features of c++ somehow involve classes or templates. These are wonderful features except for the way the compiler transforms these into object code. Most compilers use name mangling, and the ones that don't do something at least as messy.
If your system lives on its own, as is the case with many applications, then C++ is a fine choice.
If your system needs to interact with software not neccesarily written in C++ (most frequently in assembler, or Fortran Libraries) then you are in a tight spot. To interact with those kinds of cases, you'll need to disable name mangling for those symbols. this is usually done by declaring those objects extern "C", but then they can't be templates, overloaded functions, or classes. If those are likely to be your applications API, then you'll have to wrap them with helper functions, and keep those functions in sync with the actual implementations.
And in reality, the C++ language provides a standard syntax for features that can be easily implemented in pure C.
In short, the overhead of interoperable C++ is too high for most folks to justify.
Oh my, C vs C++, a great way to start a flame war. :)
I think C is better for driver and embedded code.
C++ has some great features that C doesn't have, but many of the object oriented features of C++ can cause monumental coding messes when people write code with non-obvious side-effects that occur behinds the scenes. Crazy code can be hidden in constructors, destructors, virtual functions, ... The beauty of C code is the language does nothing non-obvious behind your back, thus you can read the code and not have to look up at every constructor and destructor and so on. A lot of the problem is bad coding practices by SOME people.
My perfect language would be a combination of C99 plus a minimal subset of safer C++ capabilities that adds ZERO (or near zero) compiler overhead to the binary output. Perfect additions would be class encapsulation and naming concepts of data and functions.
One remark about "just use the subset of C++ you want to use": the problem with this idea is that it has a cost to enforce that everybody in the project uses the same subset. My own opinion is that those costs are quite high for loosely coupled projects (e.g. open source ones), and also that C++ totally failed at being a better C, in the sense that you cannot use C++ wherever you used C.
I haven't been able to find much evidence as to why you would want to choose C over C++.
You can hardly call what I'm about to say evidence; it's just my opinion.
People like C because it fits nicely inside the mind of the prgrammer.
There are many complex rules of C++ [when do you need virtual destructors, when can you call virtual methods in a constructor, how does overloading and overriding interact, ...], and to master them all takes a lot of effort. Also, between references, operator overloading and function overloading, understanding a piece of code can require you to understand other code that may or may not be easy to find.
A different question in why organizations would prefer C over C++. I don't know that, I'm just a people ;-)
In the defense of C++, it does bring valuable features to the table; the one I value most is probably parametric('ish) polymorphism, though: operations and types that takes one or more types as arguments.
I would say that C gives you better control over optimization and efficiency than C++ and hence would be useful in situations where memory and other resources are limited and every optimization helps. It also has a smaller footprint of course.
There's also the approach some shops take of using some of C++'s features in a C-like way, but avoiding ones that are objectionable. For example, using classes and class methods and function overloading (which are usually easy for even C diehards to cope with), but not the STL, stream operators, and Boost (which are harder to learn and can have bad memory characteristics).
Because you're writing for a system where resources are tight (such as an embedded system, or some kind real bare metal code like a kernel) and you want as little overhead as possible.
There's a reason why most embedded systems don't have a C++ compiler - it's not that people don't want one, it's that cramming C++ code into that small a space is task that approaches impossible.
Until some years ago the existing C++ compilers were missing important features, or the support was poor and the supported features vary wildly among them, and so it was hard to write portable applications.
Because of the no standard naming of symbols it is difficult for other languages/applications to support C++ classes directly.
What C needed was a better preprocessor.
cfront was one and thus born c++
I'ld use C, where the 'c++ as preprocessor' would not be okay.
I'm pretty sure, at the bottom of any well written c++ library/framework/toolkit,
you would find dirty-old-c ( or static casts, which is same )
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I've seen a lot of questions around that use improperly the expression "C/C++".
The reasons in my opinion are:
Newbie C and C++ programmers probably don't understand the difference between the two languages.
People don't really care about it since they want a generic, quick and "dirty" answer
While C/C++ could sometimes be interpreted as "either C or C++", I think it's a big error. C and C++ offer different approaches to programming, and even if C code can be easily implemented into C++ programs I think that referring to two separate languages with that single expression ( C/C++ ) is wrong.
It's true that some questions can be considered either as C or C++ ones, anyway.
What do you think about it?
C/C++ is a holdout from the early days of C++, where they were much more similar than they were today. It's something that wasn't really wrong at first, but is getting more-so all the time.
The basic structure is similar enough that most simple questions do still work between the two, though. There is an entire Wikipedia article on this topic: http://en.wikipedia.org/wiki/Compatibility_of_C_and_C%2B%2B
The biggest fallacy that comes from this is that because someone is well-versed in C, they will be equally good at C++.
Please remember that the original implementations of C++ were simply as a pre-compiler that output C code for the 'real' compiler. All C++ concepts can be manually coded (but not compiler-enforced) in plain C.
"C/C++" is also valid when referring to compilers and other language/programming tools. Virtually every C++ compiler available will compile either - and are thus referred to as "C/C++" compilers. Most have options on whether to treat .C and .CPP files based on the extension, or compile all of them as C or all of them as C++.
Also note that mixing C and C++ source in a single compiler project was possible from the very first C/C++ compiler. This is probably the key factor in blurring the line between the languages.
Many language/programming tools that are created for C++ also work on C because the language syntax is virtually identical. Many language tools have separate Java, C#, Python versions - but they have a single "C/C++" version that works for C and C++ due to the strong similarities.
We in our company have noticed the following curious fact: if a job applicant writes in his CV about "advanced C/C++ knowledge", there is usually a good chance that he really knows neither ;)
The two languages are distinct, but they have a lot in common. A lot of C code would compile just fine on a C++ compiler. At the early-student level, a lot of C++ code would still work on a C compiler.
Note that in some circumstances the meaning of the code may differ in very subtle ways between the two compilers, but I suppose that's true in some circumstances even between different brands of C++ compiler if you're foolish enough to rely on undefined or contested/non-conformant behavior.
Yes and no.
C and C++ share a lot in common (in fact, the majority of C is a subset of C++).
But C is more oriented "imperating programming", whereas C++, in addition to C paradigm, has more paradigms easily accessible, like functional programing, generic programing, object oriented programing, metaprograming.
So I see the "C/C++" item saying either as "the intersection of C and C++" or "familiarity with C programing as well as C++ programing", depending on the context.
Now, the two languages are really different, and have different solutions to similar problems. A C developer would find it difficult to "parse/understand" a C++ source, whereas a C++ developer would not easily recognize the patterns used in a C source.
Thus, if you want to see how far the C is from the C++ in the "C/C++" expression, a good comparison would be the GTK+ C tutorials, and the same in C++ (GTKmm):
C : GTK+ Hello World: http://library.gnome.org/devel/gtk-tutorial/stable/c39.html#SEC-HELLOWORLD
C++ : GTKmm Hello World: http://www.gtkmm.org/docs/gtkmm-2.4/docs/tutorial/html/sec-helloworld.html
Reading those sources is quite enlightening, as they are, as far as I parsed them, producing exactly the same thing, the "same" way (as far as the languages are concerned).
Thus, I guess the C/C++ "expression" can quite be expressed by the comparison of those sources.
:-)
The conclusion of all this is that it is Ok if used on the following contexts:
describing the intersection of C and C++
describing familiarity with C programing as well as C++ programing
describing compatible code
But it would not be for:
justifying keeping to code in a subset of C++ (or C) for candy compatibility with C (or C++) when compatibility is not desired (and in most C++ project, it is not desired because quite limitating).
asserting that C and C++ can/should be coded the same way (as NOT shown by the GTK+/GTKmm example above)
I think it's more of the second answer - they want something that's easily integrated into their project.
While a C answer may not be idiomatic C++ (and vice versa), I think that's one of C++'s big selling points - you can basically embed C into it. If an idiomatic answer is important, they can always specify C/C++/C++ with STL/C++ with boost/etc.
An answer in lisp is going to be pretty unusable. But an answer in either C or C++ will be directly usable.
Yeah, C/C++ is pretty useless. It seems to be a term mostly used by C++ newbies. We C-only curmudgeons just say "C" and the experienced C++ folks know how much it has diverged from C and so they properly say "C++".
Even if C is (nearly) a subset of C++, this doesn't really have any bearing on their actual usage. Practically every interesting C feature is frowned upon in modern C++ code:
C pointers (use iterators/smart pointers/references instead), macros (use templates and inline functions instead), stdio (use iostreams instead), etc. etc.
So, as Alex Jenter put it, it's unlikely that anyone who knows either language well would say C/C++. Saying that you know how to program in "C/C++" is like saying you know how to program in "Perl/PHP"... sure they've got some significant similarities, but the differences in how they are actually used are vast.
C/C++ often means a programiing style, which is like C and classes, or C and STL :-) Technicaly it is C++, but minimum of its advantages are used.
I agree. I read the C tag RSS feed, and I see tons of C++ questions come through that really don't have anything to do with C.
I also see this exchange a lot:
Asker: How do you do this in C?
Answer: Use the X library for C++.
Asker: OK, how about someone actually answer my question in C?
I use that term myself, and it is because it is my style, I don't use boost, stl or some other things, not even standard C++ libs, like "cout" and "cin", I program C but using classes, templates and other (non-library) features to my advantage.
I can say that I am not a master of C, neither a master of C++, but I am really good at that particular style that I use since 10 years ago. (and I am still improving!)
I was under the impression that all c code is valid c++ code.
Isn’t saying “C/C++” wrong?
No, it isn't. Watcom International Corporation for example, founded more than 25 years ago, called their set of C and C++ compilers and tools "Watcom C/C++", and this product is still developed and available in the open-source form as OpenWatcom C/C++
If it is a complex question needing to write more than one function, yes, it can be wrong.
If it is just to ask a detail about sprintf or bit manipulation, I think it can be legitimate (the latter can even be tagged C/C++/Java/C#, I suppose...).
Whoever is asking the question should write C, C++ or C/C++ depending on the question.
From what I've seen, you can write C++ code the C way or the C++ way. Both work, but C++ code that is not written C style is usually easier to maintain in the long run.
In the end, it all depends on the particular question. If someone is asking how to concatenate strings, than it is very important whether he wants C or C++ solution. Or, another example, if someone is asking for a qsort algorithm. To support different types, you might want to use macros with C and templates with C++, etc.
This was too long for a comment, so I had to make it an answer, but it's in response to Jeff B's answer.
Please remember that the original
implementations of C++ were simply as
a pre-compiler that output C code for
the 'real' compiler.
I have a friend (who writes C++ compilers -- yes, plural), who would take offense to your first sentence. A compiler whose object code is C source code is every bit as much a compiler as any other. The essence of a compiler is that it understands that syntax of the language, and generates new code based on that. A pre-processor has no knowledge of the language and merely reformats its input.
Remember that the C Compilers which would compile the output of those C++ compilers, would themselves output ASM code would would then be run through an assembler.
I tend to put C / C++ in my questions.
Typically I am looking for something that I can use in my c++ application.
If the code is in C or in C++ then I can use it, so I would rather not just limit the possible answers to one or the other.
Not only these two languages are different, but also the approaches are different. C++ is an OO language, while C is procedural language.
Do I have to mention templates?
Also, there are differences in C and C++ standards. If something is good in C, doesn't have to compile in C++