Question

I have the file long_arithm.cpp:

#ifndef LONG_ARITHM.CPP
#define LONG_ARITHM.CPP

#include <iostream>
#include <list>

namespace long_arithm {

    typedef signed char schar;
    enum { error_char = 127 };

    class longint {
    public:
        longint() : minusSign(0), array() { }
        longint(int num) { fromInt(num); }
        longint(std::string str) { fromString(str); }
        longint(const longint& other) : minusSign(other.minusSign), array(other.array) { }

        void fromInt(int num);
        void fromString(std::string str);

    protected:
        schar digtochar(schar num);
        schar chartodig(schar ch);

        inline bool isDigit(schar ch) { /* code */ }
        inline bool isSpaceChar(schar ch) { /* code */ }

    private:
        bool minusSign;
        std::list<schar> array;
    };
};


void long_arithm::longint::fromInt(int num) {
    /* code */
}

void long_arithm::longint::fromString(std::string str) {
    /* code */

long_arithm::schar long_arithm::longint::digtochar(schar num) {
    /* code */
}

long_arithm::schar long_arithm::longint::chartodig(schar ch) {
    /* code */
}

#endif

Now I’m trying build it, but I have errors (1st and 2nd lines – Eclipce header):

Building target: long_arithmetics
Invoking: Cross G++ Linker
g++  -o "long_arithmetics"  ./long_arithm.o ./main.o   
./main.o: In function `long_arithm::longint::fromInt(int)':
/home/gxoptg/Документы/My works/Developing/C++/long_arithmetics/Debug/../long_arithm.cpp:153: multiple definition of `long_arithm::longint::fromInt(int)'
./long_arithm.o:/home/gxoptg/Документы/My works/Developing/C++/long_arithmetics/Debug/../long_arithm.cpp:153: first defined here
./main.o: In function `long_arithm::longint::fromString(std::basic_string<char, std::char_traits<char>, std::allocator<char> >)':
/home/gxoptg/Документы/My works/Developing/C++/long_arithmetics/Debug/../long_arithm.cpp:168: multiple definition of `long_arithm::longint::fromString(std::basic_string<char, std::char_traits<char>, std::allocator<char> >)'
./long_arithm.o:/home/gxoptg/Документы/My works/Developing/C++/long_arithmetics/Debug/../long_arithm.cpp:168: first defined here
./main.o: In function `long_arithm::longint::chartodig(signed char)':
/home/gxoptg/Документы/My works/Developing/C++/long_arithmetics/Debug/../long_arithm.cpp:204: multiple definition of `long_arithm::longint::chartodig(signed char)'
./long_arithm.o:/home/gxoptg/Документы/My works/Developing/C++/long_arithmetics/Debug/../long_arithm.cpp:204: first defined here
./main.o: In function `long_arithm::longint::digtochar(signed char)':
/home/gxoptg/Документы/My works/Developing/C++/long_arithmetics/Debug/../long_arithm.cpp:188: multiple definition of `long_arithm::longint::digtochar(signed char)'
./long_arithm.o:/home/gxoptg/Документы/My works/Developing/C++/long_arithmetics/Debug/../long_arithm.cpp:188: first defined here

(Note, the line links (like :188) are broken, because I threw out a lot of commented lines of code.)

Why I have that errors and what I should correct? As good as I understand,

void fromInt(int num);

and others are ‘pre-definitions’, and I don’t see any other definitions of that methods.

Thank you for help.

Answer 1

The functions that are defined outside of the class definition must either be moved to a source (.cpp) file or you must use the inline keyword at the front of them. Otherwise a copy of the function is placed into each source file that includes the header and marked as available to other modules, and the linker complains when there’s more than one.