cin not working with empty string when_GLIBCXX_DEBUG on Windows?

Question

Very Strange behavior happened to me. I am using latest Cygwin32, Cygwin64 and MinGW32 with GCC 4.9.2 , 4.9.2 and 4.8.1 respectively on Windows 7 64-bit. I am testing also on 32-bit Linux using GCC 4.8.2.

So on all systems this works

#include <bits/stdc++.h>
using namespace std;
string s,t;
int main(){
  cin>>s>>t;
  cout<<s;
}

and this works

#define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
using namespace std;
string s="a",t="b";
int main(){
    cin>>s>>t;
    cout<<s;
}

but the next one crashes on Windows after inputting the first string on the 3 configurations mentioned above, but works correctly on Linux:

#define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
using namespace std;
string s,t;
int main(){
    cin>>s>>t;
    cout<<s;
}

Clearly the only difference is that the string is empty before inputting, and _GLIBCXX_DEBUG is enabled.

First, is this a reproducible problem? i.e. does it happen on every PC with the same configuration , or only my PC? Second, What is the problem? What should I do? I clearly need _GLIBCXX_DEBUG to debug other STL structures in the code.

Answer 1

_GLIBCXX_DEBUG changes ABI of STL classes (i.e. layout of structs, including streams and std::string):

To use the libstdc++ debug mode, compile your application with the compiler 
flag -D_GLIBCXX_DEBUG. Note that this flag changes the sizes and behavior of 
standard class templates such as std::vector, and therefore you can only link 
code compiled with debug mode and code compiled without debug mode if no 
instantiation of a container is passed between the two translation units.

(from official docs).

Your app (compiled with _GLIBCXX_DEBUG) passes std::string to std::cin::operator >> in libstdc++.dll (compiled without this macro) and thus violates the requirement above. Such violations normally manifest in runtime crashes: see this or this for concrete examples.