std::basic_string is undefined in Xcode 16.3

I just upgraded from Xcode 16.2 to Xcode 16.3, compiling with C++11.

I have been using this definition for years:

typedef std::basic_string<unsigned char> ustring;

But now, apparently, this functionality has been removed? Indeed, I see in the header for char_traits.h:

struct char_traits; /*The Standard does not define the base template for char_traits because it is impossible to provide etc etc

It had been working up until I upgraded my compiler, as a "temporary" definition had been provided.

The error message now is this:

implicit instantiation of undefined template 'std::char_traits<unsigned char>'

I tried just copying the temp definition from the headers of 16.2, but when I compile I get this error:

/Applications/Xcode-16.3.0.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.4.sdk/usr/include/c++/v1/string:821:42: error: implicit instantiation of undefined template 'std::char_traits<unsigned int>'821 | static_assert(is_same<_CharT, typename traits_type::char_type>::value,

I definitely have no definition of std::char_traits<unsigned int>, and I have never had it. It compiled before, and now it doesn't with the same, unchanged code, even when I copy the missing part from the previous header.

Not sure what to do. I'm surprised it's so difficult just to declare a std::string with an unsigned char (I use them everywhere in code to denote UTF-8 strings).

I know that C++20 has char8_t, but my app is MONUMENTAL and I just need a quick fix to get my ustring defined again in C++11.

Anyone have a drop-in replacement for C++11 in Xcode 16.3?

A minimal app is this:

#include <string>typedef std::basic_string<unsigned char> ustring;void    main(){    ustring     str((const unsigned char *)"hello");    printf("%s\n", (const char *)str.c_str());}