undefined reference to template function [duplicate]

Answer 1

You have 2 ways:

1. Implement convert2QString in util.h.

2. Manually instantiate convert2QString with int in util.cpp and define this specialization as extern function in util.h

util.h

namespace Util
{
    template
    QString convert2QString(T type , int digits=0);

    extern template <> QString convert2QString(int type , int digits);
}

util.cpp

 namespace Util {
     template
     QString convert2QString(T type, int digits)
     {
         using std::string;

         string temp = (boost::format("%1") % type).str();

         return QString::fromStdString(temp);
     }

     template <> QString convert2QString(int type , int digits); 
}