GCC 的 wchar_t 有多大?

2022-01-11 00:00:00 gcc macros c++

GCC 支持 -fshort-wchar 将 wchar_t 从 4 转换为两个字节.

GCC supports -fshort-wchar that switches wchar_t from 4, to two bytes.

在编译时检测 wchar_t 大小的最佳方法是什么，以便我可以将其正确映射到适当的 utf-16 或 utf-32 类型?至少，在 c++0x 发布并为我们提供稳定的 utf16_t 和 utf_32_t 类型定义之前.

What is the best way to detect the size of wchar_t at compile time, so I can map it correctly to the appropriate utf-16 or utf-32 type? At least, until c++0x is released and gives us stable utf16_t and utf_32_t typedefs.

#if ?what_goes_here?
  typedef wchar_t Utf32;
  typedef unsigned short Utf16;
#else
  typedef wchar_t Utf16;
  typedef unsigned int Utf32;
#endif

推荐答案

你可以使用宏

__WCHAR_MAX__
__WCHAR_TYPE__

它们由 gcc 定义.您可以使用 echo "" | 检查它们的值.gcc -E - -dM

They are defined by gcc. You can check their value with echo "" | gcc -E - -dM

由于 __WCHAR_TYPE__ 的值可以从 int 到 short unsigned int 或 long int，最好恕我直言，您的测试是检查 __WCHAR_MAX__ 是否高于 2^16.

As the value of __WCHAR_TYPE__ can vary from int to short unsigned int or long int, the best for your test is IMHO to check if __WCHAR_MAX__ is above 2^16.

#if __WCHAR_MAX__ > 0x10000
  typedef ...
#endif

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