Description of problem:

Define _GLIBCXX_USE_CXX11_ABI gets ignored by gcc in devtoolset-7.
As a result the old CoW-String Implementation is used. But I need the new SSO-String-Implementation.
Also the old implementation of std::list is used. See https://stackoverflow.com/questions/47951367/d-glibcxx-use-cxx11-abi-1-ineffective-for-devtoolset-7-on-centos-7 for another person who has the same problem.

Version-Release number of selected component (if applicable):

devtoolset-7 on RHEL7

How reproducible:

Program to reproduce:

#include <string>
#include <iostream>
#include <type_traits>

int main()
{
   std::cout << "_GLIBCXX_USE_CXX11_ABI=" << _GLIBCXX_USE_CXX11_ABI << std::endl;
   std::cout << "std::is_base_of<std::__sso_string, std::string>::value: " << std::is_base_of<std::__sso_string, std::string>::value << std::endl;
   std::cout << "sizeof(std::string): " << sizeof(std::string) << std::endl;
   return 0;
}


Actual results:

$ scl enable devtoolset-7 bash
$ g++ --version
g++ (GCC) 7.2.1 20170829 (Red Hat 7.2.1-1)
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
$ g++ --std=c++11 -D_GLIBCXX_USE_CXX11_ABI=1 cxx_abi_test.cpp 
[haegele@localhost source]$ ./a.out 
_GLIBCXX_USE_CXX11_ABI=0
std::is_base_of<std::__sso_string, std::string>::value: 1
sizeof(std::string): 8
$ g++ --std=c++11 -D_GLIBCXX_USE_CXX11_ABI=0 cxx_abi_test.cpp 
$ ./a.out 
_GLIBCXX_USE_CXX11_ABI=0
std::is_base_of<std::__sso_string, std::string>::value: 1
sizeof(std::string): 8

As you can see the define _GLIBCXX_USE_CXX11_ABI gets overwritten somewhere magically.

Expected results:

I tested with gcc (SUSE Linux) 7.1.1 20170607 [gcc-7-branch revision 248970]

$ g++ -std=c++11 -D_GLIBCXX_USE_CXX11_ABI=1 cxx_abi_test.cpp
haegele@Dev-05:~/source> ./a.out
_GLIBCXX_USE_CXX11_ABI=1
std::is_base_of<std::__sso_string, std::string>::value: 1
sizeof(std::string): 32
$ g++ -std=c++11 -D_GLIBCXX_USE_CXX11_ABI=0 cxx_abi_test.cpp
haegele@Dev-05:~/source> ./a.out
_GLIBCXX_USE_CXX11_ABI=0
std::is_base_of<std::__sso_string, std::string>::value: 0
sizeof(std::string): 8

Additional info:

I suspect this is somehow on purpose to get compatibility with RHEL6 which doesn't support _GLIBCXX_USE_CXX11_ABI=1. However, in my case I don't care about RHEL6. I just want GCC7 on RHEL7 and that's why I'm using the devtoolset-7.