OSX vs Linux: how to deal with unsigned long and uint64_t?

Question

The following code

#include <cstdio>
#include <cstdint>
#include <type_traits>

int main()
{
    static const char* b2s[] = { "no", "yes" };
    printf( "%s\n", b2s[std::is_same<unsigned long, uint64_t>::value] ); 
}

returns yes when compiled on Linux, and no when compiled on OSX.

I read while trying on understand why that this was apparently normal . How can I deal with this if I am developing a library and that I want it to be portable? Will I have to deal with each OS's preference?

Here is an example:

foo.h

#include <cstdint>

template <class T>
struct Foo
{
    static const char id;
};

foo.cpp

#include "foo.h"
#define DEFINE_FOO(type_,id_)                           \
    template <> const char Foo<type_>::id = id_;        \
    template <> const char Foo<const type_>::id = id_;

DEFINE_FOO(    bool,'a')
DEFINE_FOO(  int8_t,'b')
DEFINE_FOO( uint8_t,'c')
DEFINE_FOO( int16_t,'d')
DEFINE_FOO(uint16_t,'e')
DEFINE_FOO( int32_t,'f')
DEFINE_FOO(uint32_t,'g')
DEFINE_FOO( int64_t,'h')
DEFINE_FOO(uint64_t,'i')
DEFINE_FOO(   float,'j')
DEFINE_FOO(  double,'k')

// OSX requires this, but Linux considers it a re-definition
// DEFINE_FOO(unsigned long,'l')

As part of my library, the previous is compiled and then linked when I need to create an executable (say main.cpp ). Typically, this looks like:

$(CC) -c -Wall -std=c++0x -o foo.o foo.cpp
$(CC) -Wall -std=c++0x -o main main.cpp foo.o

That will work on one platform but fail in the other; if I uncomment DEFINE_FOO(unsigned long,'l') in foo.cpp then OSX is happy, but Linux says Foo<uint64_t> is being redefined. And vice-versa.

How can that be normal? Is there a "portable" way to deal with this?

Answer 1

In order to make it portable, I'd enclose the macro calls with #ifdef conditionals according to the target OS using this list , such as:

#ifdef __linux__
DEFINE_FOO(uint64_t,'l')
#endif
[...]
#ifdef __APPLE__
DEFINE_FOO(unsigned long,'l')
#endif

Note that I set uint64_t as l since unsigned long and uint64_t are pretty much equivalent in 64bit architectures with gcc.