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I have declared a template function in .h file and defined in a .cpp file and calling the function from another .cpp file.

i am getting the following error

/tmp/ccJg5vwy.o: In function main': main.cpp:(.text+0x8f): undefined reference toshort temp < int, std::allocator < int > >(std::__cxx11::list > const&)'

collect2: error: ld returned 1 exit status

my files are:

//main.cpp

#include"a.h"
#include<iostream>
#include<list>
using namespace std;

int main(){
    list<int> arr(5);
    for (int i=0;i<5;i++)
        arr.push_back(i);
    fun1();
    fun2();
    temp(arr);
    return 0;
}

//a.h

#include <list>
using namespace std;
void fun1();
void fun2();
template <class L ,class A>
    short temp(const list<L,A>& val);

//fun2.cpp

#include"a.h"
#include<iostream>
using namespace std;
void fun2(){
    cout<<"I am in function2\n";
}

//a.cpp

#include "a.h"
#include<iostream>
using namespace std;
void fun1()
{
        cout<<"I am in function1\n";
}
template <class L,class A>
    short temp(const list<L,A>& val){
        cout<<"inside the template function\n";
        typename list<L,A>::const_iterator iter=val.begin();
         while (iter != val.end())
                {
                       cout<< *iter << endl;
                       ++iter;
                }
         cout<<"leaving the template function\n";
            return 0;
    }

and i am compiling the files in the following format

g++ a.cpp fun2.cpp main.cpp

I am not getting why there is a linking problem.

I have also tried by changing a.cpp and a.h to the following format but still i am getting the error

//a.cpp

#include "a.h"
#include<iostream>
using namespace std;
void fun1()
{
    cout<<"I am in function1\n";
}
template <class L>
    short temp(const list<L>& val){
        cout<<"inside the template function\n";
        typename list<L>::const_iterator iter=val.begin();
        while (iter != val.end())
                {
                       cout<< *iter << endl;
                       ++iter;
                }
         cout<<"leaving the template function\n";
            return 0;
    }

//a.h

#include <list>
using namespace std;
void fun1();
void fun2();
template <class L>
short temp(const list<L>& val);

in this case error is

/tmp/cce0eJj9.o: In function main': main.cpp:(.text+0x8f): undefined reference toshort temp< int >(std::__cxx11::list > const&)' collect2: error: ld returned 1 exit status

Ayush Sahu
  • 11
  • 3
  • You can not declare template functions in header and define in .cpp. Only in headers or include .cpp after declare. – Mister_Jesus Feb 19 '18 at 13:47
  • @MrBin: Yes you can. But it's a bit of a complicated matter. See the linked answers. – Sebastian Mach Feb 19 '18 at 14:07
  • @SebastianMach, i wrote the same thing at the end. – Mister_Jesus Feb 19 '18 at 14:28
  • @MrBin: The same as what? I just wrote "see the linked answers". And including source files is the same as including header files. If you're funny, you can also name it "foo.h" and "foo.frob". The compiler does not principally differentiate header files from source files. The key points to understand are ODR (One Definition Rule) explicit instantiation. – Sebastian Mach Feb 19 '18 at 15:19

0 Answers0