Call a CPP struct in c

**biswa** · 03-05-2015

Hello everyone
I have a cpp project which has a struct defined in header file as

Code:

namespace ZWApi {
   struct ZWNode {
        int typeBasic;
	int typeGeneric;
	int typeSpecific;
	bool sleepingDevice;
	int plutoDeviceTemplateConst;
	int stateBasic;
	time_t pingtime;
	std::string associationList[4];
    };
}

I have a C file which needs this struct.i want to call ZWNode struct in c and create a struct called pNode.

So far I have managed to link cpp and c files...Now i am trying to create the new struct pNode as

struct ZWApi::ZWNode pNode;

but i am having an error :error: expected identifier or ‘(’ before ‘:’ token
struct ZWApi::ZWNode pNode;
WHat am I doing wrong...I hope i made my problem clear..any suggestions appreciated...thankss

**Salem** · 03-05-2015

C knows nothing of bool or std::string.

How to mix C and C++, C++ FAQ

**laserlight** · 03-05-2015

The scope resolution operator :: is C++ syntax: it cannot be used in a C program. Even if you declared the C++ struct to be in the global namespace, you may still have the problem of name mangling, hence the use of extern "C" for C linkage. The thing is though, you cannot write this in the header:

Code:

#ifdef __cplusplus
extern "C"
{
#endif
    struct ZWNode
    {
        /* ... */
        std::string associationList[4];
    };
#ifdef __cplusplus
}
#endif

since if it gets included in the C source file, you once again have the problem of C++ syntax in a C compilation unit, and besides, you'll need to #include <string> in the header.

I may be mistaken, but I suppose that you will have to write a C++ wrapper around ZWApi::ZWNode that has C linkage through extern "C" and uses no C++-specific constructs, e.g., because uses the opaque pointer idiom such that the interface is provided as a set of non-member non-friend functions with C linkage that accept the opaque pointer as an argument.

**rstanley** · 03-05-2015

Originally Posted by Salem

C knows nothing of bool or std::string.

How to mix C and C++, C++ FAQ

Not true for bool. The data type 'bool' was added to the C99 Standard, along with 'true' == 1, and 'false' == 0.

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