[RESOLVED] template function in non-template class

[JohnnyTest]

I am trying to implement BigInteger library by myself. I am storing numbers in std::string.
The header file (BigInt.h) contains:

#ifndef BIGINT_H
#define BIGINT_H

#include <iostream>
//#include <vector>

/**Specifications:
*   Constructor: can take, int, string(formatted as number), float or double
*   operators to define +, -, *, /, %, power(), <<, >>
*/

class BigInt
{
public:
    /** Default constructor */
    BigInt();


    /** string constructor */
    BigInt(const std::string&);


    /** int, float or double constructor */
    template<typename T>
    BigInt(const T&);

    /** Default destructor */
    virtual ~BigInt();

    /** Copy constructor
     *  \param other Object to copy from
     */
    BigInt(const BigInt& other);

    /** Assignment operator
     *  \param other Object to assign from
     *  \return A reference to this
     */
    BigInt& operator=(const BigInt& other);

    /**
    *   Overloaded << ostream operator
    */
    friend std::ostream& operator<<(std::ostream& os, const BigInt& bigInt);

protected:

private:
    /**
    *   Number is represented as:
    *   +0.123324 or -0.1232432
    *   +123 or -123 etc
    *   [+ or -] then [numbers] then maybe [.] then [more numbers]
    */
    std::string dec_rep;
};

#endif // BIGINT_H

definition of member functions is in BigInt.cpp:

#include "BigInt.h"

#include <string>
#include <regex>
//#include <sstream>

BigInt::BigInt()
{
    //ctor
    dec_rep = "+0";
}

template<typename T>
BigInt::BigInt(const T& n)
{
    dec_rep = std::to_string(n);
    if( dec_rep[0] != '+' && dec_rep[0]!='-')
    {
        dec_rep = "+" + dec_rep;
    }
}


/**
* it accepts input as string if it is correctly formatted as number
* accepted forms are: 1234, 1.234, +1233, +1.234, 0.234, .234, +.234, -123 etc
* these are unaccepted; --123, +-23, -+32, 0.234.0 or any other wrong format
*/
BigInt::BigInt(const std::string& str)
{
    std::regex re("[-+]?([0-9]*\\.[0-9]+)"); //regular expression to check if input is in proper format
    std::smatch m;
    if(std::regex_match(str, m, re))
    {
        dec_rep = str;
        if((str[0] == '+' || str[0] == '-') && str[1] == '.')
        {
            dec_rep = dec_rep[0] + "0" + dec_rep.substr(1);
        }
        else if(str[0] == '.')
        {
            dec_rep = "+0" + dec_rep;
        }
        else if(str[0]>='0' && str[0]<='9')
        {
            dec_rep = "+" + dec_rep;
        }
    }
}

BigInt::~BigInt()
{
    //dtor
}

BigInt::BigInt(const BigInt& other)
{
    //copy ctor
}

BigInt& BigInt::operator=(const BigInt& rhs)
{
    if (this == &rhs) return *this; // handle self assignment
    //assignment operator
    return *this;
}

std::ostream& operator<<(std::ostream& os, const BigInt& bigInt)
{
    os<<bigInt.dec_rep;
    return os;
}

main() is in main.cpp:

#include <iostream>

#include "BigInt.h"

using namespace std;

int main()
{
    BigInt n(1);  //Line 9 where 1st error comes
    BigInt n_default;
    BigInt str_n("1"); //Line 11 where 2nd error comes
    cout<<n<<" "<<n_default<<" "<<str_n<<endl;
    cout << "Hello world!" << endl;
    return 0;
}

When I try to run it, it shows following errors:
obj/Debug/main.o||In function `main':|
1. undefined reference to `BigInt::BigInt<int>(int const&)' on line 9 of main.cpp
2. undefined reference to `BigInt::BigInt<char [2]>(char const (&) [2])' on line 11 of main.cpp
3. error: ld returned 1 exit status
||=== Build failed: 3 error(s), 0 warning(s) (0 minute(s), 0 second(s)) ===|

I'm using code-blocks 16.01 with GCC compiler on Linux Mint 18.2 'Sonya' (64 bit).