哪些平台不在 type_info op== 中使用字符串比较？

Question

这是type_info::operator==的典型实现：

#if _PLATFORM_SUPPORTS_UNIQUE_TYPEINFO
    bool operator==(const type_info& __rhs) const {
      return __mangled_name == __rhs.__mangled_name;
    }
#else
    bool operator==(const type_info& __rhs) const {
      return __mangled_name == __rhs.__mangled_name ||
             strcmp(__mangled_name, __rhs.__mangled_name) == 0;
    }
#endif

在 libstdc++ 中，它由 __GXX_MERGED_TYPEINFO_NAMES、
控制在 libc++ 中是 _LIBCPP_NONUNIQUE_RTTI_BIT,
MSVC 总是比较字符串。

不比较字符串的平台有哪些？

Answer 1

In libstdc++ it's controlled with __GXX_MERGED_TYPEINFO_NAMES

In newer versions of gcc (since 23 Jul 2009) this macro is set to 0 by default. It always compares pointers first and if that fails they do the full string comparison. See here:

We used to do inline pointer comparison by default if weak symbols are available, but even with weak symbols sometimes names are not merged when objects are loaded with RTLD_LOCAL, so now we always use strcmp by default.

哪些平台不在 type_info op== 中使用字符串比较？

Which platforms don't use string comparison in type_info op==?

c++

rtti

typeid

typeinfo