-std=c++ 98 and OS X 10.10 - c++

Question

I'm currently trying to compiling my program with the -std=c++98 flag on OS X 10.10:
clang++ -std=c++98 -pedantic -W -Wall -Werror *.cpp
g++ -std=c++98 -pedantic -W -Wall -Werror *.cpp
Strangely when I compile with OS 10.10 no error are showed while some are showed with a GNU/Linux distribution.
With the GNU/Linux distribution I have some errors because I use s.open(file); instead of s.open(file.c_str()); but on OS X no error, even by using s.open(file);.
Maybe there is just a link between this error and the filesystem of each OS?

Answer 1

You're correct. This code shouldn't compile under C++98:
#include <fstream>
#include <string>
int main() {
std::string file("/tmp/foo.txt");
std::ifstream s;
s.open(file);
}
It's technically a bug in libc++, but it's one that I doubt that they will want to fix.
If you wanted, you could compile with libstdc++ as the standard library, which doesn't have this feature implemented (at least the version that apple distributes doesn't).
[10:13am][wlynch#watermelon /tmp] clang++ -std=c++98 -stdlib=libstdc++ foo.cc
foo.cc:7:12: error: no viable conversion from 'std::string' (aka 'basic_string<char>') to 'const char *'
s.open(file);
^~~~
/usr/include/c++/4.2.1/fstream:518:24: note: passing argument to parameter '__s' here
open(const char* __s, ios_base::openmode __mode = ios_base::in)
^
1 error generated.

Answer 2

The problem is that on OS X you're still using a C++11 implementation of the standard library, which includes such API changes as the ostream::open method accepting std::strings.
Changing the C++ standard with -std=c++98 does not affect the standard library being used, and libc++ does not implement C++98 (e.g., there's no #ifdef to remove those open(std::string) APIs when in C++98 mode) whereas I think libstdc++ does hide non-c++98 APIs when building in C++98 mode.