C++ Struct function in an another header gives "missing type specifier"

Question

I got in my "main.cpp" the following code:

#include "rational.h"

using namespace std;

typedef struct rational {
    long long numerator;
    long long denominator;
} rational_t;

And I have a Header-file namend "rational.h":

#pragma once


rational add(rational  a,rational b)
{
    rational c;
    c.numerator = a.numerator + b.numerator;
    c.denominator = a.denominator + b.denominator;
    return c;
}

I got an Error on Line:

rational add(rational  a,rational b)

It gives me the following Error-Code: Fehler C4430 Fehlender Typspezifizierer - int wird angenommen. Hinweis: "default-int" wird von C++ nicht unterstützt. Translation: Error C4430 Missing Type specifier - int is accepted. "default-int" is not supported by C++.

I think because the function does not detect my struct properly. Can anyone pls help me?

Greetings, Nike

The struct declaration should go in the header file. Also decide if you want proper c or c++ language. c requires `struct rational` while c++ does not. — πάντα ῥεῖ, Dec 11 '16 at 11:48

Andrew Weir · Answer 1 · 2016-12-11T12:07:08.160

You haven't pasted your full source code for main.cpp and rational.h, so this makes it a little harder to debug properly. Based only on what you've given:

Your structure was called "rational" but you've used typedef and defined it as a new type, or another way of declaring a "struct rational" called rational_t. Your function should return a rational_t, and accept rational_t for both parameters.
You likely meant to put the struct rational into rational.h, ahead of your function declaration.

It's pretty hard to determine if you want to use C++ or C from this example code too, so I've written it up in C. It'll be a start for you to learn from.

main.c

#include <stdlib.h>
#include <stdio.h>

#include "rational.h"

int main() 
{
    rational_t first;
    rational_t second;

    first.numerator = 5;
    first.denominator = 7;

    second.numerator = 3;
    second.denominator = 9;

    rational_t product = add(first, second);
    printf("%lld / %lld\n", product.numerator, product.denominator);

    return 0;
}

rational.h

#ifndef RATIONAL_H_
#define RATIONAL_H_

typedef struct rational {
    long long numerator;
    long long denominator;
} rational_t;

rational add(rational  a,rational b)
{
    rational c;
    c.numerator = a.numerator + b.numerator;
    c.denominator = a.denominator + b.denominator;
    return c;
}

#endif // RATIONAL_H_

You_'ve written it up in C_ not - your code is C++, since in `rational add(rational a,rational b)` a structure tag is used as a type name, which is invalid in C. — Armali, Aug 16 '18 at 09:08

C++ Struct function in an another header gives "missing type specifier"

1 Answers1