How to pass struct from c++ to function in c?

Question

I have a C++ file which is like below:

int myNum[10] = {10, 20, 20, 40, 50, 60, 70, 80, 90, 100};

struct rfid
{
    int AntennaID;
    char *tid;
};

for (int i = 0; i < 10; i++) {
    AntennaID = myNum[i];

    struct rfid p1 = {AntennaID, tid};

    cout << "roll no : " << p1.AntennaID << endl;
    cout << "roll no : " << p1.tid << endl; 
    passInfo(*p1);
}

And I have a C file, which is like below:

#include <stdio.h>

void passInfo(*p1)
{
    printf("%s :: \n", *p1);
}

How to pass the structure which is framed in C++ to a function of C?

passInfo is a function which is in c file. Have used extern c to in c++ file to access the function. — Mahamutha M
– Mahamutha M, Commented Jun 17, 2020 at 6:48
void passInfo(*p1) does this even compile? you did not specify type of *p1 — Tony Tannous
– Tony Tannous, Commented Jun 17, 2020 at 6:49
No, its not. I dont know, how to achieve my result for this. I am not aware of c & c++ functionalities. — Mahamutha M
– Mahamutha M, Commented Jun 17, 2020 at 6:51
The question is unclear. You have a .cpp file and a .h file ? or .cpp and .c? What compiler? — Tony Tannous
– Tony Tannous, Commented Jun 17, 2020 at 6:53

score 1 · Accepted Answer · 2020-06-17 07:15:51Z

1

Make a header that will compile for both C and C++.

// shared.h
typedef struct rfid_
{
    int AntennaID;
    char *tid;
} rfid;

#if defined __cplusplus
extern "C"
#endif
void passInfo(rfid *p1);

Implement your function in C.

// c.c
#include <stdio.h>
#include "shared.h"

void passInfo(rfid *p1) 
{
    // whatever you want
}

Use your function in C++ by including the header.

// cpp.cpp
#include <iostream>
#include "shared.h"

int test()
{
    int myNum[10] = {10, 20, 20, 40, 50, 60, 70, 80, 90, 100};

    for (int i = 0; i < 10; i++) {
        AntennaID = myNum[i];
        rfid p1 = {AntennaID, tid};
        cout << "roll no : " << p1.AntennaID << endl;
        cout << "roll no : " << p1.tid << endl;
        passInfo(&p1);
    }
}

edited Jun 17, 2020 at 7:15

answered Jun 17, 2020 at 6:58

user13540365

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6 Comments

Remy Lebeau Over a year ago

In c.c, void passInfo(rfid *p1) needs to be void passInfo(struct rfid *p1). The code would be cleaner if shared.h defined typedef struct rfid rfid; under C, instead of using 2 #ifs on the passInfo() declaration.

KamilCuk Over a year ago

#if !defined __cplusplus struct #endif is not needed.

user13540365 Over a year ago

@RemyLebeau I will modify the answer.

Remy Lebeau Over a year ago

@KamilCuk yes, it is. Under C, struct type names must always be prefixed with struct. That is not needed in C++.

KamilCuk Over a year ago

Not needed, but if you write it, nothing happens ; ) I meant just to leave void passInfo(struct rfid *p1). I meant the #if !defined __cplusplus and #endf are not needed around struct.

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