c++ - C ++中的固定宽度整数文字？

Question

C++11 首次引入了对通过用户定义的文字在 C++ 中定义新文字的支持。C++11 或更高版本是否还为 in 中的类型预定义了固定宽度整数文字的后缀<cstdint>？

Answer 1

不。从 C++14 开始，标准定义的唯一文字后缀由标准库中的<chrono>,<complex>和<string>标头提供。标<chrono>头为持续时间定义 , , , , , 后缀，为h虚min数s定义ms,us和后缀，为文字定义后缀。ns<complex>iilif<string>sbasic_string

但是，可以像这样轻松定义自己的固定宽度文字：

#include <cstdint>

constexpr std::int8_t operator "" _int8(unsigned long long v)
{ return static_cast<std::int8_t>(v); }

constexpr std::uint8_t operator "" _uint8(unsigned long long v)
{ return static_cast<std::uint8_t>(v); }

constexpr std::int16_t operator "" _int16(unsigned long long v)
{ return static_cast<std::int16_t>(v); }

constexpr std::uint16_t operator "" _uint16(unsigned long long v)
{ return static_cast<std::uint16_t>(v); }

constexpr std::int32_t operator "" _int32(unsigned long long v)
{ return static_cast<std::int32_t>(v); }

constexpr std::uint32_t operator "" _uint32(unsigned long long v)
{ return static_cast<std::uint32_t>(v); }

constexpr std::int64_t operator "" _int64(unsigned long long v)
{ return static_cast<std::int64_t>(v); }

constexpr std::uint64_t operator "" _uint64(unsigned long long v)
{ return static_cast<std::uint64_t>(v); }

constexpr std::int_fast8_t operator "" _int_fast8(unsigned long long v)
{ return static_cast<std::int_fast8_t>(v); }

constexpr std::uint_fast8_t operator "" _uint_fast8(unsigned long long v)
{ return static_cast<std::uint_fast8_t>(v); }

constexpr std::int_fast16_t operator "" _int_fast16(unsigned long long v)
{ return static_cast<std::int_fast16_t>(v); }

constexpr std::uint_fast16_t operator "" _uint_fast16(unsigned long long v)
{ return static_cast<std::uint_fast16_t>(v); }

constexpr std::int_fast32_t operator "" _int_fast32(unsigned long long v)
{ return static_cast<std::int_fast32_t>(v); }

constexpr std::uint_fast32_t operator "" _uint_fast32(unsigned long long v)
{ return static_cast<std::uint_fast32_t>(v); }

constexpr std::int_fast64_t operator "" _int_fast64(unsigned long long v)
{ return static_cast<std::int_fast64_t>(v); }

constexpr std::uint_fast64_t operator "" _uint_fast64(unsigned long long v)
{ return static_cast<std::uint_fast64_t>(v); }

constexpr std::int_least8_t operator "" _int_least8(unsigned long long v)
{ return static_cast<std::int_least8_t>(v); }

constexpr std::uint_least8_t operator "" _uint_least8(unsigned long long v)
{ return static_cast<std::uint_least8_t>(v); }

constexpr std::int_least16_t operator "" _int_least16(unsigned long long v)
{ return static_cast<std::int_least16_t>(v); }

constexpr std::uint_least16_t operator "" _uint_least16(unsigned long long v)
{ return static_cast<std::uint_least16_t>(v); }

constexpr std::int_least32_t operator "" _int_least32(unsigned long long v)
{ return static_cast<std::int_least32_t>(v); }

constexpr std::uint_least32_t operator "" _uint_least32(unsigned long long v)
{ return static_cast<std::uint_least32_t>(v); }

constexpr std::int_least64_t operator "" _int_least64(unsigned long long v)
{ return static_cast<std::int_least64_t>(v); }

constexpr std::uint_least64_t operator "" _uint_least64(unsigned long long v)
{ return static_cast<std::uint_least64_t>(v); }

constexpr std::intmax_t operator "" _intmax(unsigned long long v)
{ return static_cast<std::intmax_t>(v); }

constexpr std::uintmax_t operator "" _uintmax(unsigned long long v)
{ return static_cast<std::uintmax_t>(v); }

constexpr std::intptr_t operator "" _intptr(unsigned long long v)
{ return static_cast<std::intptr_t>(v); }

constexpr std::uintptr_t operator "" _uintptr(unsigned long long v)
{ return static_cast<std::uintptr_t>(v); }

警告：如果在不适合的文字上使用上面的代码会默默地给出错误的结果unsigned long long，如果文字值不适合请求的类型，例如999_int8. 一个更好的实现（GPL-3 许可）可能必须逐个字符地解析文字并static_assert在溢出时，像这样。

使用用户定义文字的缺点是需要在后缀前加上下划线_，因为根据 §17.6.4.3.4 保留不带下划线的后缀以供将来标准化。