Why this program is compiling with gcc but not with g++?

Question

Following Program compiles with gcc but not with g++, I am generating only object file.

This is prog.c:

#include "prog.h"

static struct clnt_ops tcp_nb_ops = {4}; 

This is prog.h:

#ifndef _PROG_
#define _PROG_

#include <rpc/rpc.h>

#endif

When I do:

gcc -c prog.c

That generates object code but,

g++ -c prog.c

gives error:

variable ‘clnt_ops tcp_nb_ops’ has initializer but incomplete type

How to solve this issue?

Answer 1

Look at the definition of this struct in clnt.h:

typedef struct CLIENT CLIENT;
struct CLIENT {
  AUTH  *cl_auth;        /* authenticator */
  struct clnt_ops {
    enum clnt_stat (*cl_call) (CLIENT *, u_long, xdrproc_t, caddr_t, xdrproc_t, caddr_t, struct timeval);
    /* ...*/
  } *cl_ops;
    /* ...*/
};

As you can see, the struct clnt_ops is defined inside struct CLIENT. So the proper name for this type in C++ is CLIENT::clnt_ops. In C, however there is no such thing as nested structs, so it is visible as simply struct clnt_ops.

If you want to be portable you may add something along the lines of:

#ifdef __cplusplus
    typedef CLIENT::clnt_ops clnt_ops;
#else
    typedef struct clnt_ops clnt_ops;
#endif

clnt_ops tcp_nb_ops = ...;

But I think that this type is simply not intended to be used directly by client code. Instead use whole struct CLIENT only.