Using C-style struct/typedef from within C++

Question

I have a project that is mixing C and C++. In a C header file, I have code like this:

typedef struct mystruct* mystruct;
struct mystruct {
    // whatever struct needs
};

And to use this in the C++ file, I am doing:

extern "C" {
#include "mystruct.h"
}

So you see that I am creating an opaque pointer using the same names. This is fine in C but not in C++ (because of the requirement to instantiate using the struct keyword in C but not in C++). However, I get an error (conflicting declarations) when trying to compile the C++ code. I thought that using the extern "C" would make the compiler treat the C header as C, but it seems to still be using it as C++. Is there any explanation for what is happening here?

score 11 · Accepted Answer · answered Jul 12 '11 at 20:37

11

I thought that using the extern "C" would make the compiler treat the C header as C

No. The only thing that extern "C" does is control name mangling. The code is still compiled as C++ (though things that require mangled names, such as namespaces or templates, won’t work). In particular, the rule concerning struct identifiers still applies.

answered Jul 12 '11 at 20:37

Konrad Rudolph

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Can you please elaborate the term `control name mangling` ? I amn't sure what it means. Thanks. – Mahesh Jul 12 '11 at 20:39
6

@Mahesh “control” is a verb. `extern "C"` *controls* [name mangling](http://en.wikipedia.org/wiki/Name_mangling). – Konrad Rudolph Jul 12 '11 at 20:49

score 1 · Answer 2 · answered Jul 12 '11 at 20:38

1

extern "C" enforces C linkage, as opposed to mangled C++ linkage. extern "C" does not enforce full C compliance such as dynamically sizable arrays, etc.

answered Jul 12 '11 at 20:38

totowtwo

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Using C-style struct/typedef from within C++

2 Answers2