The solution is probably to (1) simply replace setlocale with std::setlocale, and (2) copy the old locale name so it won't be clobbered by subsequent calls to setlocale. We should actually use mitk::LocaleSwitch whenever possible.

I'm not sure about this, http://en.cppreference.com/w/cpp/locale/setlocale says that a copy of the returned string can be used to restore locale, not string itself.

There is a pull request #140 that replaces all setlocale() calls with mitk::LocaleSwitch guard but it may be an overkill.

It's definitely enough to use std::string instead of char* to store returned value:

const std::string previousCLocale = setlocale(LC_NUMERIC, nullptr);
setlocale(LC_NUMERIC, "C");

It will create an independent copy of previous locale that isn't spoiled by future calls.

Yes, sorry, we just read it completely and I edited my comment above accordingly.

In itself I would not call replacing all locale calls with mitk::LocalSwitch overkill, only tedious. However looking at
https://github.com/MITK/MITK/pull/140

I do see one issue, which would keep me from accepting it as is:

What is the purpose of
https://github.com/MITK/MITK/pull/140/commits/d088f34cc30628d81723a7728b5c754f626e673c#diff-52e7f9c2c949eb22cf2c898c143fff18L18

You add

#include "mitkLogMacros.h"
#include <string>
#pragma warning(disable:4251)

I would hesitate to add includes to such a widely included header.

#include <string> is required to use std::string.
#include "mitkLogMacros.h" is required to use MITK_INFO.
Otherwise all files that include "mitkLocaleSwitch.h" will have to include both <string> and "mitkLogMacros.h" as well.

It's possible to remove "mitkLogMacros.h" if move implementation to .cpp file from mitkLocaleSwitch.h.

#pragma warning(disable:4251) is required to stop compiler warning about std::string export:

class 'std::basic_string<char,std::char_traits<char>,std::allocator<char>>' needs to have dll-interface to be used by clients of struct 'mitk::LocaleSwitch'

mitkMimeType.h already uses this pragma in slightly different way:

#ifdef _MSC_VER
#pragma warning(push)
#pragma warning(disable:4251)
#endif

So, I'll:

1. Split mitk::LocaleSwitcher into .h and .cpp files
2. Move "#include "mitkLogMacros.h" to .cpp
3. Try to deal with 4251 warning in more elegant way.

I vote for

1. Move implementation to .cpp file
2. Remove std::string dependency in header by using the Pimpl idiom and change the signature of the ctor, which should be explicit btw.

@kuznetsov Do you want to do it or should we do it? Both really is okay for us, I'm just asking because we don't want to "take away" a contribution from you of course.

I'll do it.
Also, Pimpl will fix 4251 warning as well, as far as I understand.

Cool, thank you. Here's a nice example of the Pimpl idiom in MITK:

https://phabricator.mitk.org/diffusion/MITK/browse/master/Modules/Core/include/mitkPropertyFilter.h
https://phabricator.mitk.org/diffusion/MITK/browse/master/Modules/Core/src/DataManagement/mitkPropertyFilter.cpp

Don't forget to delete the impl pointer in the dtor of the actual class. It's a raw pointer instead of a std::unique_ptr because that would lead to the 4251 warning again.

Just saw the update on GitHub. A minor thing: Please initialize the impl in the initializer list of the ctor instead of in the ctor body, thank you!

Done.