The FAQ Board

[medievalelks]

Found this on the FAQ board and it should probably be amended or removed, as it is misleading at best:

FAQ Difference between C, C++ and C#

C++ - a "better C" (Stroustrop, guy who made it). It is an extension of C. All good C programs are also C++ programs, but the reverse is not true. Contains elements that generally make large scale programming easier.

C and C++ may be related, but they are different languages with different standards and different design goals. And there are myriad "good C programs" that are not C++ programs.

A fun experiment would be to download any moderately sized C project from SourceForge and try to compile it with a C++ compiler.

[SlyMaelstrom]

C and C++ may be related, but they are different languages with different standards and different design goals. And there are myriad "good C programs" that are not C++ programs.

While I agree that the wording should be changed, the point was that everything that can be compiled in C can be compiled in C++. It was designed that way (even references to C libraries)... however, I am reading it and getting the feeling as though it's saying "Don't use C! C++ is like C, only better!"

Should be changed.

[medievalelks]

While I agree that the wording should be changed, the point was that everything that can be compiled in C can be compiled in C++.

No, that is simply not true.

http://david.tribble.com/text/cdiffs.htm

When we say that C is incompatible with C++ with respect to a specific language feature, we mean that a C program that employs that feature either is not valid C++ code and thus will not compile as a C++ program, or that it will compile as a C++ program but will exhibit different behavior than the same program compiled as a C program. In other words, an incompatible C feature is valid as C code but not as C++ code.

[Mario F.]

No, that is completely untrue.

No. It's not. It may be untrue for some cases. It's not completely untrue.

For a lighter reading: http://en.wikipedia.org/wiki/Compati...nd_C%2B%2B
For a more detailed description: http://david.tribble.com/text/cdiffs.htm

Also GNU caters many of these differences in the form of C++ compiler extensions.

On those cases remaining where it may still not be possible to compile C code as C++ it is often due to the lack of will on behalf of the programmer to change his C code. There may be some cases where it is still not possible.

But in general terms code for C compiles as C++. And that was the meaning. It is correct. Not completely untrue as you say.

[SlyMaelstrom]

No, that is simply not true.

http://david.tribble.com/text/cdiffs.htm

I'm not sure of any specific examples of C code that will not compile with a C++ compiler. I know of several situations where certain C code might exibit undefined behavior in a C++ compiler (specifically regarding dynamic memory allocation and such)... however, I would like to see an example of standard C99 code that a C++ compiler won't compile (whcih is the only thing I suggested in my post). The exception being, of course, the use of C++ keywords as identifiers in a C program.

[Prelude]

>I would like to see an example of standard C code that a C++ compiler won't compile

char *p = malloc ( 10 );

[medievalelks]

No. It's not. It may be untrue for some cases. It's not completely untrue

The statement that everything that is valid C is also valid C++ - is completely untrue. It is a false statement, with no shades of grey.

[Mario F.]

char *p = malloc ( 10 );

pedantically speaking, yes. it won't compile.

[Mario F.]

The statement that everything that is valid C is also valid C++ - is completely untrue. It is a false statement, with no shades of grey.

extern c

[medievalelks]

pedantically speaking, yes. it won't compile.

There's nothing pedantic about it. It either compiles or does not.

Sorry, but it's time to kill the myth that C++ is a superset of C.

[medievalelks]

extern c

You've already been given one counter-example, and there are plenty more. Therefore, it's false (i.e. completely untrue) to say that everything that is valid C is also valid C++.

I'm not sure why this is so difficult.

[SlyMaelstrom]

>I would like to see an example of standard C code that a C++ compiler won't compile

char *p = malloc ( 10 );

Yes, that's true... for some reason I was thinking implicit casts would only generate a warning and not an error (It's been too long since I've used C code). I couldn't say there are PLENTY more exampels of this... but there is certainly this and perhaps a few more. This is, as far as I know, the only example of C code that will not compile in C++ and can be found in a practical C application (that is to say, people aren't doing strange things just to make the compiler give an error)

[Mario F.]

You've already been given one counter-example, and there are plenty more. Therefore, it's false (i.e. completely untrue) to say that everything that is valid C is also valid C++.

Look medievaleks, we may agree to disagree. That's is also a good starting point.

The problem is how you and I are reading "everything" in the context of the full post. I know, as you do, not all C code compiles in C++. I read everything as "in general terms". You prefer to adopt "everything" at face value.

As I said before in general terms C code can be compiled as C++. With a little bit of effort you can use compiler extensions, extern c and changes to the code to produce satisfying results. There may be some code that simply can't be compiled, period. But generally it can if you want.

Contraty to you, I don't think " it's time to kill the myth that C++ is a superset of C". First because i'm unsure there is such a myth, second because it won't be us here that will suddenly change the world.

I however also agree with you. And that is because for anyone not in the know (and that is only anyone just now learning C or C++. Say... 6 months of practice?) "everything" can be seen as... everything.

[Prelude]

>I couldn't say there are PLENTY more exampels of this...
You didn't ask for "PLENTY" though, you asked for one. I could give you well more than plenty for the current state of the standards though. C++ hasn't caught up to C99 yet, and C99 is being used in practical applications.

Here's the reality:

C and C++ are not 100% syntactically or semantically compatible. As such, you can't take any C program and compile it as C++. However, often you need little more than minor changes to compile C as C++, especially if the C code was written with C++ compatibility in mind.

[medievalelks]

Yes, that's true... for some reason I was thinking implicit casts would only generate a warning and not an error (It's been too long since I've used C code). I couldn't say there are PLENTY more exampels of this... but there is certainly this and perhaps a few more. This is, as far as I know, the only example of C code that will not compile in C++ and can be found in a practical C application (that is to say, people aren't doing strange things just to make the compiler give an error)

Anything that names an identifier using a keyword introduced by C++ (e.g. new, delete) would fail to compile. The article I linked points out a lot more. Keep in mind that there was C code written decades before C++ was created.