What differences, if any, between C++03 and C++11 can be detected at run-time?

Question

It is possible to write a function, which, when compiled with a C compiler will return 0, and when compiled with a C++ compiler, will return 1 (the trivial sulution with

Answer 1

This isn't quite a correct example, but it's an interesting example that can distinguish C vs. C++0x (it's invalid C++03 though):

 int IsCxx03()
 {
   auto x = (int *)0;
   return ((int)(x+1) != 1);
}

Answer 2

#include <utility>

template<typename T> void test(T t) { t.first = false; }

bool isCpp0x()
{
   bool b = true;
   test( std::make_pair<bool&>(b, 0) );
   return b;
}

Answer 3

Though not so concise... In current C++, class template name itself is interpreted as a type name (not a template name) in that class template's scope. On the other hand, class template name can be used as a template name in C++0x(N3290 14.6.1/1).

template< template< class > class > char f( int );
template< class > char (&f(...))[2];

template< class > class A {
  char i[ sizeof f< A >(0) ];
};

bool isCpp0x() {
  return sizeof( A<int> ) == 1;
}

Answer 4

I got an inspiration from What breaking changes are introduced in C++11?:

#define u8 "abc"

bool isCpp0x() {
   const std::string s = u8"def"; // Previously "abcdef", now "def"
   return s == "def";
}

This is based on the new string literals that take precedence over macro expansion.

Answer 5

Unlike prior C++, C++0x allows reference types to be created from reference types if that base reference type is introduced through, for example, a template parameter:

template <class T> bool func(T&) {return true; } 
template <class T> bool func(...){return false;} 

bool isCpp0x() 
{
    int v = 1;
    return func<int&>(v); 
}

Perfect forwarding comes at the price of breaking backwards compatibility, unfortunately.

Another test could be based on now-allowed local types as template arguments:

template <class T> bool cpp0X(T)  {return true;} //cannot be called with local types in C++03
                   bool cpp0X(...){return false;}

bool isCpp0x() 
{
   struct local {} var;
   return cpp0X(var);
}

Answer 6

From this question:

struct T
{
    bool flag;
    T() : flag(false) {}
    T(const T&) : flag(true) {}
};

std::vector<T> test(1);
bool is_cpp0x = !test[0].flag;