How to deal with noexcept in Visual Studio
I'm trying to create a custom exception that derives from std::exception and overrides what() . At first, I wrote it like this:
class UserException : public std::exception
{
private:
const std::string message;
public:
UserException(const std::string &message)
: message(message)
{}
virtual const char* what() const override
{
return message.c_str();
}
};
This works fine in VS2012, but it doesn't compile in GCC 4.8 with -std=c++11 :
error: looser throw specifier for 'virtual const char* UserException::what() const'
So I add noexcept :
virtual const char* what() const noexcept override
This works fine in GCC, but it doesn't compile in Visual Studio (because VS 2012 doesn't support noexcept ):
error C3646: 'noexcept' : unknown override specifier
What is the recommended way to deal with this? I want the same code to compile with both compilers and I'm using C++11 features, so I can't compile with different -std .
Use a macro
#ifndef _MSC_VER
#define NOEXCEPT noexcept
#else
#define NOEXCEPT
#endif
And then define the function as
virtual const char* what() const NOEXCEPT override
You could also modify that to allow noexcept on later versions of VS by checking the value of _MSC_VER ; for VS2012 the value is 1600.
"noexcept" is only supported since the Visual Studio 2015 (as stated here: https://msdn.microsoft.com/en-us/library/wfa0edys.aspx). I have used following code with Visual Studio 2013 (derived from above examples):
#if !defined(HAS_NOEXCEPT)
#if defined(__clang__)
#if __has_feature(cxx_noexcept)
#define HAS_NOEXCEPT
#endif
#else
#if defined(__GXX_EXPERIMENTAL_CXX0X__) && __GNUC__ * 10 + __GNUC_MINOR__ >= 46 ||
defined(_MSC_FULL_VER) && _MSC_FULL_VER >= 190023026
#define HAS_NOEXCEPT
#endif
#endif
#ifdef HAS_NOEXCEPT
#define NOEXCEPT noexcept
#else
#define NOEXCEPT
#endif
This check works to see if noexcept is supported:
// Is noexcept supported?
#if defined(__clang__) && __has_feature(cxx_noexcept) ||
defined(__GXX_EXPERIMENTAL_CXX0X__) && __GNUC__ * 10 + __GNUC_MINOR__ >= 46 ||
defined(_MSC_FULL_VER) && _MSC_FULL_VER >= 180021114
# define NOEXCEPT noexcept
#else
# define NOEXCEPT
#endif
The above works with Clang, GCC and MSVC.
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