Splitting class definition in .h and .cpp file

Question

following standards, I splitted class definition in two files, these are they

fraction.h

#ifndef FRACTION_H
#define FRACTION_H

#include <string>
#include <cmath>
#include <climits>
using std::string;
using std::log10;
using std::ceil;


class fraction
{
private:
    int __max_arr_len = (int)ceil(log10(__LONG_MAX__));
    long numerator;
    long denomenator;
    string convertion(long _num);

public:
    void reduce();
    inline void set_numerator(long _new);
    inline void set_denominator(long _new);
    inline long get_numerator();
    inline long get_denominator();
    inline double get_fraction();
    inline string get_str_fraction();
    fraction(long _num, long _den);
};

#endif // FRACTION_H

fraction.cpp

#include "fraction.h"

long gcd(long _f, long _s) {

    if (_f % _s == 0)

        return _s;

    return gcd(_s, _f % _s);
}

string fraction::convertion(long _num) {

    char *arr = new char[this->__max_arr_len];
    int ind = 0;

    while (_num > 0) {

        *(arr + ind++) = (char)(30 + _num % 10);
        _num /= 10;
    }

    for (auto iter = arr; iter < arr + this->__max_arr_len; ++iter) {

        char temp = *iter;
        *iter = *(arr + this->__max_arr_len - 1 - (iter - arr));
        *(arr + this->__max_arr_len - 1 - (iter - arr)) = temp;

    }

    return string(arr);
}

fraction::fraction(long _num, long _den)
{

    this->denomenator = _den;
    this->numerator = _num;

}

void fraction::reduce() {

    long _gcd = gcd(this->numerator, this->denomenator);

    this->denomenator /= _gcd;
    this->numerator /= _gcd;


}

inline void fraction::set_denominator(long _new) { this->denomenator = (_new != 0) ? _new : this->denomenator; }
inline void fraction::set_numerator(long _new) { this->numerator = _new; }
inline long fraction::get_denominator() { return this->denomenator; }
inline long fraction::get_numerator() { return this->numerator; }
inline double fraction::get_fraction() { return (double) this->numerator / this->denomenator; }
inline string fraction::get_str_fraction() { return convertion(this->numerator) + '/' + convertion(this->denomenator); }

The problem is, including header in my main.cpp still leaves unresolved reference, linker says there is no definition for class members.

I've seen many examples where this approach works, yet leaving me in wondering how, since no explicit reference to class.cpp has been present.

The question is more about how does linker knows which source file contains definition for a class that has a template in header.

Looks like I'm missing something, any suggestions?

Help much appreciated.

P.S. never tested it so no idea if this works without any runtime errors. just started learning OOP.

EDIT_1: output of g++:

In file included from main.cpp:2:
fraction.h:25:17: warning: inline function ‘long int fraction::get_denominator()’ used but never defined
   25 |     inline long get_denominator();
      |                 ^~~~~~~~~~~~~~~
/usr/bin/ld: /tmp/ccvEpbJj.o: in function `main':
main.cpp:(.text+0x35): undefined reference to `fraction::get_denominator()'
collect2: error: ld returned 1 exit status

Please edit your question to include the exact commands you're running to build your program. — Joseph Sible-Reinstate Monica, Oct 27 '21 at 14:39
You need to link the compiled fraction.cpp with your program. For small projects you can just list all the .cpp files in one command: `g++ ... main.cpp fraction.cpp` — Dúthomhas, Oct 27 '21 at 14:40
See this on the usage of `inline`: https://stackoverflow.com/a/1759575/1643973 — jjramsey, Oct 27 '21 at 14:41
using Qt Creator to build the project, I can include makefile, any use of it? — Fungor, Oct 27 '21 at 14:44
You need to include `main.cpp` and `fraction.cpp` somehow into the project, But I have no idea what Qt Creator is and how it works — Jabberwocky, Oct 27 '21 at 14:45
This won't answer your question but you should avoid 'using x' in header files as it will include it when you include your header file. You should use the full namespace and class name in a header e.g. std::string — Simon Newman, Oct 27 '21 at 14:46
edited with output of compiler, think there is no problem in Qt — Fungor, Oct 27 '21 at 14:49
Your `convertion` is both unreadable, unnecessary, and leaks memory. `std::to_string` already exists. — molbdnilo, Oct 27 '21 at 14:57

Splitting class definition in .h and .cpp file

0 Answers0