c++ - undefined reference to template function

The implementation of a non-specialized template must be visible to a translation unit that uses it.

The compiler must be able to see the implementation in order to generate code for all specializations in your code.

This can be achieved in two ways:

1) Move the implementation inside the header.

2) If you want to keep it separate, move it into a different header which you include in your original header:

util.h

namespace Util
{
    template
    QString convert2QString(T type , int digits=0);
}
#include "util_impl.h"

util_impl.h

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


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

            return QString::fromStdString(temp);
        }
}