Question

My third question here today ;-), but I am really new to c++ template programming and operator overloading.

I am trying the following:

terminallog.hh

//snipped code

class Terminallog {
public:

    Terminallog();
    Terminallog(int);
    virtual ~Terminallog();

    template <class T>
    Terminallog & operator<<(const T &v);
    template <class T>
    Terminallog & operator<<(const std::vector<T> &v);
    template <class T>
    Terminallog & operator<<(const T v[]);
    Terminallog & operator<<(const char v[]);

//snipped code
};

//snipped code
template <class T>
Terminallog &Terminallog::operator<<(const T &v) {
    std::cout << std::endl;
    this->indent();
    std::cout << v;
    return *this;
}

template <class T>
Terminallog &Terminallog::operator<<(const std::vector<T> &v) {
    for (unsigned int i = 0; i < v.size(); i++) {
        std::cout << std::endl;
        this->indent();
        std::cout << "Element " << i << ": " << v.at(i);
    }
    return *this;
}

template <class T>
Terminallog &Terminallog::operator<<(const T v[]) {
    unsigned int elements = sizeof (v) / sizeof (v[0]);
    for (unsigned int i = 0; i < elements; i++) {
        std::cout << std::endl;
        this->indent();
        std::cout << "Element " << i << ": " << v[i];
    }
    return *this;
}

Terminallog &Terminallog::operator<<(const char v[]) {
    std::cout << std::endl;
    this->indent();
    std::cout << v;
    return *this;
}
//snipped code

Trying to compile this code, it gives me a linker error:

g++ src/terminallog.cc inc/terminallog.hh testmain.cpp -o test -Wall -Werror 
/tmp/ccifyOpr.o: In function `Terminallog::operator<<(char const*)':
testmain.cpp:(.text+0x0): multiple definition of `Terminallog::operator<<(char const*)'
/tmp/cccnEZlA.o:terminallog.cc:(.text+0x0): first defined here
collect2: ld returned 1 exit status

Therfore I am currently banging my head against the wall, searching for a solution. But I can’t find one in the wall…

It would be great if someone could show me my mistake

Thank you so much

ftiaronsem

Answer 1

This function

Terminallog &Terminallog::operator<<(const char v[]) {
    std::cout << std::endl;
    this->indent();
    std::cout << v;
    return *this;
}

is not a template, but a regular member function. If this .h file is included in several .cpp filtes, it will cause the multiple definition error you’re seeing. If you declare it inline, the compiler will allow the multiple definitions and your error should be fixed.

inline
Terminallog &Terminallog::operator<<(const char v[]) {