I am trying to convert C++11 code to C++03 and stuck on a default template argument.
#include <type_traits>
#include <boost/utility/enable_if.hpp>
#include <boost/type_traits/is_const.hpp>
#include <boost/type_traits/conditional.hpp>
#include <boost/spirit/home/support/string_traits.hpp>
template<bool B, class T = void>
struct enable_if {};
template<class T>
struct enable_if<true, T> { typedef T type; };
template<typename T>
struct is_char
{
typedef typename enable_if<sizeof (T) == sizeof (char)>::type eif;
};
template<bool B, class T, class F>
struct conditional { typedef T type; };
template<class T, class F>
struct conditional<false, T, F> { typedef F type; };
template <typename ObjType,
typename PtrType,
typename CharType =
typename conditional<boost::is_const<PtrType>::value,
const typename ObjType::char_type,
typename ObjType::char_type>::type,
typename is_char<PtrType>::type >
CharType* char_ptr_cast(PtrType* p)
{ return reinterpret_cast<CharType*>(p); }
int main ()
{}
I am getting following error:
> /usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/c++0x_warning.h:31:2:
> error: #error This file requires compiler and library support for the
> upcoming ISO C++ standard, C++0x. This support is currently
> experimental, and must be enabled with the -std=c++0x or -std=gnu++0x
> compiler options.
>
> test.cc:35: error: no default argument for anonymous
>
> **default template arguments may not be used in function templates without -std=c++0x or -std=gnu++0x**
Could you please help me to resolve these errors?
Default template arguments for function templates were added in C++11. If you can't use C++11, or your compiler doesn't support it properly, you can't define typename CharType = /* whatever */
. The way towards C++03 compliance without retyping that long meta-function is to refactor CharType
into its own trait, and use that.
template<typename ObjType, typename PtrType>
struct CharType {
typedef typename conditional<boost::is_const<PtrType>::value,
const typename ObjType::char_type,
typename ObjType::char_type>::type
type;
};
template <typename ObjType typename PtrType>
typename CharType<ObjType, PtrType>::type* char_ptr_cast(PtrType* p)
{ return reinterpret_cast<typename CharType<ObjType, PtrType>::type*>(p); }
Also, the <type_traits>
header is a C++11 only header. Since you hit a #error
directive following a failed standard's version check in the standard library, that is the most likely culprit. You cannot include it.
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