CODEWITHSUNDEEP
c++cstringwrappermember-functions
user4950013
user4950013

Reputation: 137

wrapper function in throwing error " as ‘p’ was not declared in this scop"

I am trying to access C++ function (f1) and string a from c file using a wrapper function. Code below.

Error thrown is

Error : error: ‘p’ was not declared in this scope double d = f11( p,i);

1.h

double f11(struct c* p, int i);

1.cpp

#include<iostream>
using namespace std; 
class c
{
    public:   double f1(int i)  // how can i access from c 
    {
        cout<<"I am in c++";
    }
    public : string a;   // how can i access string from c
};

extern "C"  double f11(c* p, int i) // wrapper function
{
    return p->f1(i);
}

2.c

#include<stdio.h>
#include "1.h"
int main()
{
    int i=9;
    double d = f11( p,i);
}

Upvotes: 3

Views: 303

Answers (1)

R Sahu
R Sahu

Reputation: 206627

If you manually include the contents of "1.h" in main.cpp, it would look:

#include <stdio.h>

double f11(struct c* p, int i);

int main()
{
    int i=9;
    double d = f11( p,i);
}

There are several problems there.

  1. You haven't declared p before using it in the call to f11.

  2. You don't have any way of constructing an object of type struct c in main. Even if you were to fix the compiler errors by providing declarations of struct c and p, you'll run into run time problems since the only way to initialize p will be to initialize it to NULL. That wouldn't do you any good since you have a line

    return p->f1(i);

    in f11.

  3. Your declaration and definition of f11 will result in linker error. If you want to implement the function as extern "C", you'll also have to declare it as extern "C".

    extern "C" double f11(c* p, int i);

  4. In 1.cpp, the member function f1 does not return a double. That is cause for undefined error, if the compiler does not report that as an error.

See working code at http://ideone.com/aVFWFJ. Please note that I changed the implementation of c::f1 so it does not crash.

Upvotes: 2

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