ustring::string() returns empty string when using the new C++11 ABI

[foutrelis]

I noticed that when using GCC 5.1 with the new libstdc++ ABI enabled, oslc foo.osl (from OpenShadingLanguage) would choose .oso as the output filename instead of foo.oso.

oslc uses shader_decl()->shadername().string() + ".oso" as the default output filename if one is not provided via the -o option. Further testing indicates that OpenImageIO's ustring::string() method is broken and returns an empty string on the new C++11 ABI.

Bellow is an example test program and GDB backtrace that show the issue.

#include <OpenImageIO/ustring.h>

int main(void) {
    auto a = OpenImageIO::v1_4::ustring("123");
    std::string b = "123";

    std::cout << "a = " << a.string() << std::endl << "b = " << b << std::endl;
    return 0;
}

Breakpoint 1, main () at test.cc:8
8       std::cout << "a = " << a.string() << std::endl << "b = " << b << std::endl;

(gdb) p a
$1 = {static npos = 18446744073709551615, m_chars = 0x61d870 "123", 
  static empty_std_string = <optimized out>}

(gdb) p a.string
$2 = {const std::__cxx11::string &(const OpenImageIO::v1_4::ustring * const)} 0x4010e6 <OpenImageIO::v1_4::ustring::string[abi:cxx11]() const>

(gdb) p &a.string()
$3 = (const std::__cxx11::string *) 0x61d838

(gdb) p a.string()
$4 = ""

(gdb) c
Continuing.
a = 
b = 123

[lgritz]

Can you test this workaround? #1176

[foutrelis]

Seems to work, thanks!

Please note that most (if not all) Linux distros configure GCC 5.1 to use the old ABI (using --with-default-libstdcxx-abi=c++98). The issue won't manifest in such configurations, though building OIIO and its dependencies with -D_GLIBCXX_USE_CXX11_ABI=1 should be enough to reproduce it.