Error with a template function in a library

Projects Libraries
4

So why doesn't this work ?
the .h file

template <class T>
void printBinA(T data);

the .cpp file

#include <Arduino.h>
#include "PrintBin.h"

void printBinA(T data)
{
  for (int b = (sizeof(data) * 8) - 1; b >= 0; b--)
  {
    if ((data & (1 << b)))
    {
      Serial.print(1);
    }
    else
    {
      Serial.print(0);
    }
  }
}

the test sketch

#include "PrintBin.h"

void setup()
{
  Serial.begin(115200);
  int var = 0b0101010110101010;
  printBinA(var);
}

void loop()
{
}

the error message

Arduino: 1.8.13 (Windows 10), Board: "Arduino Nano, ATmega328P"

PrintBin.cpp:4:16: error: variable or field 'printBinA' declared void

 void printBinA(T data)

                ^

PrintBin.cpp:4:16: error: 'T' was not declared in this scope

exit status 1

variable or field 'printBinA' declared void

This report would have more information with
"Show verbose output during compilation"
option enabled in File -> Preferences.

Ok, but I am trying to keep this simple and not have the need to create an instance of an object to use the PrintBin functions. If I simply put the template function in the .h file, like this

template <class T>
void printBinA(T data)
{
  for (int b = (sizeof(data) * 8) - 1; b >= 0; b--)
  {
    if ((data & (1 << b)))
    {
      Serial.print(1);
    }
    else
    {
      Serial.print(0);
    }
  }
}

and remove the .cpp file I can call the function perfectly well just like a non template function, but with any integer data type. However, I have seen advice previously that this is bad practice and should not be done, so I was trying to do it the correct way