basic_ifstream<...>::read() doesn't read anything - c++

Question

The program built from this code:
#include <fstream>
using std::basic_ifstream;
#include <ios>
using std::streamsize;
#include <ZenLib/Conf.h>
using ZenLib::int8u;
int main() {
#define charT int8u
#define T basic_ifstream<charT>
T ifs ("/proc/cpuinfo", T::in | T::binary);
#undef T
streamsize const bufsize (4096);
charT buf[bufsize];
#undef charT
return !ifs.read(buf, bufsize).gcount();
}
... returns 1.
So std::basic_ifstream<ZenLib::int8u>::read() could not extract any byte from /proc/cpuinfo.
Am I doing anything wrong?

Answer 1

Intantiating std::char_traits for anything but char or wchar_t is
undefined behavior (And I suspect that your charT is unsigned char,
not char.) If you want to use a different type for characters, you'll
have to define a new traits class; for std::istream anf
std::ostream, you'll also have to define a number of facets for the
type as well.
The question is what you want to do. In your example, you only call
std::istream::read. If this is the case, the simplest solution is
probably to just drop down to the system level functions. These
probably want a char* for there buffer as well, but a
reinterpret_cast from unsigned char* will work. You can do this for
std::istream<char>::read as well, but if you have an std::istream,
there's a definite possibility that some formatted input will creap in,
and that will interpret the characters before you can get your
reinterpret_cast in.

Answer 2

The stream libraries are designed to be used with the character types such as char and wchar_t, not integers:
C++11 standard: 27.2.2
In the classes of Clause 27, a template formal parameter with name
charT represents a member of the set of types containing char,
wchar_t, and any other implementation-defined character types that
satisfy the requirements for a character on which any of the iostream
components can be instantiated.
Maybe start from this:
int main()
{
std::ifstream ifs("/proc/cpuinfo", std::ios::binary);
std::cout << ifs.rdbuf();
}