"New" operator works in extern "C"

Question

Im using a C++ DLL for my C# project, DLL has a class inside which is created and destroyed by outer functions such as:

 class myClass
 {
   int N;
   public:
        //some elements and some functions

        myClass(int n)
        {
            N=n;
        }
 };

 __declspec(dllexport) myClass * builderF(int n)
 {

      return new myClass(n);

 }

 __declspec(dllexport) void destroyerF(myClass * c)
 {

      delete c;

 }

and these are in extern "C" {} body.

How does the compiler let me use C++ features is "C" space? Isnt it for only C code? This is tested and works(Ive started making an opencl wrapper for C#). I was using only pure C codes before.

May be helpful: [In C++ source, what is the effect of extern “C”?](http://stackoverflow.com/questions/1041866/in-c-source-what-is-the-effect-of-extern-c) — Shafik Yaghmour, Jul 31 '13 at 11:47
So linking is completely different than compiling? So it just compiles as a C++ code. — huseyin tugrul buyukisik, Jul 31 '13 at 11:50
This not only compiles, but really works? I mean, `destroyerF` function? o.O — lapk, Jul 31 '13 at 11:50
Yes, Im creating with an int parameter lets say "44" then reading it from C# then deleting the class by a dll-call. — huseyin tugrul buyukisik, Jul 31 '13 at 11:50
Yes. I did not copy-paste, I wrote by hand and made error :D — huseyin tugrul buyukisik, Jul 31 '13 at 11:54

score 9 · Accepted Answer · answered Jul 31 '13 at 11:50

9

extern "C" doesn't change the compiler into a C compiler. It only says that any functions (or pointers to functions) will use the C conventions in their interface. So you can still do anything you could do in C++ in the functions; it's only things like name mangling and calling conventions which will be affected.

answered Jul 31 '13 at 11:50

James Kanze

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Okay, this is more cleaner now. Thank you. Accepting in minutes. Must every compiler give exactly same behaviour? – huseyin tugrul buyukisik Jul 31 '13 at 11:52
2

Following up on James' answer, the only thing you cannot do in an `extern "C"` block is overload functions; overloading is managed via name mangling, which as James addresses, isn't there within this block. – mah Jul 31 '13 at 11:53
+1: Note that some compilers can be switched in to C-mode using directives, but this is not how. – John Dibling Jul 31 '13 at 11:53
@huseyintugrulbuyukisik It depends on what you mean by the same behavior. Every compiler is required to parse and compile the code as C++ (with certain restrictions: as mah says, you can't overload functions). What the C calling conventions are depends on the compiler, and which C compiler it is targeting (normally, the C ABI of the system, if it has one). – James Kanze Jul 31 '13 at 12:00
@JohnDibling Naming the file `.c`, instead of `.cpp`, `.cxx`, `.cc` or `.C` is normally sufficient. – James Kanze Jul 31 '13 at 12:01
@James Kanze Okay, I got it. Function parameter passing is always C++ style as I suspect. – huseyin tugrul buyukisik Jul 31 '13 at 12:02
Obviously. But that won't work when C and C++ is mixed in the same file. Not saying such a mixture should exist, just adding information. – John Dibling Jul 31 '13 at 12:03
@JohnDibling Ah. You were talking about `#pragma`, or some such. – James Kanze Jul 31 '13 at 12:23
@JamesKanze: Yup. I personally have never used them, but I know they exist. – John Dibling Jul 31 '13 at 12:25

"New" operator works in extern "C"

1 Answers1