g++ template error Small_size - c++

Question

I am working on the latest revision of the C++ programming language (think it's 5) and run into a problem with g++ version 5.2.
My code is a variation of Small_size template from chap 24.
#include <iostream>
template<int N>
bool is_small ()
{
std::cerr << sizeof(N) << std::endl;
std::cerr << N << std::endl;
return N <= 255;
}
bool ism (int i_n)
{
return i_n <= 255;
}
int main ()
{
std::cout << "hallo welt" << std::endl;
std::cout << 0 << " " << is_small<0> << std::endl;
std::cout << 255 << " " <<is_small<255> << std::endl;
std::cout << -4100000000 << " " << is_small<-4100000000> << std::endl;
std::cout << 256 << " " << is_small<256> << std::endl;
std::cout << 256 << " " << ism(256) << std::endl;
std::cout << 256 << " " << (256 <= 255) << std::endl;
}
When I compile it, it's ok. But when I run the thing, it simply seems to be broken.
[cpp11#hydra src]$ cat ~/bin/g14
#!/bin/bash
g++-52 -std=c++14 "${1}.C" -L$LIBPATH -o "$1"
[cpp11#hydra src]$ g14 konzept_small
[cpp11#hydra src]$ ./konzept_small
hallo welt
0 1
255 1
-4100000000 1
256 1 //1
256 0
256 0
[cpp11#hydra src]$
My problem is that:
the result for 256 and higher is wrong. See comment //1
there is no output of the template code on cerr
I started with a version without the cerr, but got only the wrong template result.
I removed a constexpr from the template, but no change.
So I added as last step the cerr to see whats wrong.
Any ideas?

Answer 1

You are not calling is_small<N>, but just printing out its address. You need to change your code to
std::cout << 0 << " " << is_small<0>() << std::endl;
std::cout << 255 << " " <<is_small<255>() << std::endl;
std::cout << -4100000000 << " " << is_small<-4100000000>() << std::endl;
std::cout << 256 << " " << is_small<256>() << std::endl;
Note the added (). Not sure why you are getting the output you are though, are you sure you are running the same code you posted?

Answer 2

is_small is a function you should add the parenthesis :
change
std::cout << 0 << " " << is_small<0> << std::endl;
to this
std::cout << 0 << " " << is_small<0>() << std::endl;
It worked fine for me with this change