类型何时提升为 unsigned int？
When does a type get promoted to an unsigned int?
这个article说：
If all values of the original type can be represented as an int, the
value of the smaller type is converted to an int; otherwise, it is
converted to an unsigned int
signed/unsigned char 和 signed/unsigned short 的所有值都可以表示为 int，那么什么时候类型会提升为 unsigned int？
好吧，如果 sizeof(char) == sizeof(int)，那么 unsigned char 应该提升为 unsigned int
A short 不能比 int 长，但在某些平台上它可能大小相同。 int 和 long 也是如此。这意味着如果 "smaller" 是无符号的，那么 "larger" 也必须是无符号的。
这篇文章使用了草率的术语。源类型不必是 "smaller" 而不是 int。这是 C++11 标准所说的：
A prvalue of an integer type other than bool, char16_t, char32_t, or wchar_t whose integer conversion
rank (4.13) is less than the rank of int can be converted to a prvalue of type int if int can represent all
the values of the source type; otherwise, the source prvalue can be converted to a prvalue of type unsigned int.
有些平台，例如，unsigned short 和 int 都是 16 位长。尽管如此，根据定义，unsigned short 的等级 比 int 低 并且受到积分提升。在这种情况下，int不能代表所有unsigned short类型的值，所以提升为unsigned int.
编辑：C99 有类似的措辞：
The following may be used in an expression wherever an int or unsigned int may
be used:
- An object or expression with an integer type whose integer conversion rank is less
than or equal to the rank of
int and unsigned int.
- A bit-field of type
_Bool, int, signed int, or unsigned int.
If an int can represent all values of the original type, the value is converted to an int;
otherwise, it is converted to an unsigned int. These are called the integer
promotions. 48) All other types are unchanged by the integer promotions.
这个article说：
If all values of the original type can be represented as an int, the value of the smaller type is converted to an int; otherwise, it is converted to an unsigned int
signed/unsigned char 和 signed/unsigned short 的所有值都可以表示为 int，那么什么时候类型会提升为 unsigned int？
好吧，如果 sizeof(char) == sizeof(int)，那么 unsigned char 应该提升为 unsigned int
A short 不能比 int 长，但在某些平台上它可能大小相同。 int 和 long 也是如此。这意味着如果 "smaller" 是无符号的，那么 "larger" 也必须是无符号的。
这篇文章使用了草率的术语。源类型不必是 "smaller" 而不是 int。这是 C++11 标准所说的：
A prvalue of an integer type other than
bool,char16_t,char32_t, orwchar_twhose integer conversion rank (4.13) is less than the rank ofintcan be converted to a prvalue of typeintifintcan represent all the values of the source type; otherwise, the source prvalue can be converted to a prvalue of typeunsigned int.
有些平台，例如，unsigned short 和 int 都是 16 位长。尽管如此，根据定义，unsigned short 的等级 比 int 低 并且受到积分提升。在这种情况下，int不能代表所有unsigned short类型的值，所以提升为unsigned int.
编辑：C99 有类似的措辞：
The following may be used in an expression wherever an
intorunsigned intmay be used:
- An object or expression with an integer type whose integer conversion rank is less than or equal to the rank of
intandunsigned int.- A bit-field of type
_Bool,int,signed int, orunsigned int.If an
intcan represent all values of the original type, the value is converted to anint; otherwise, it is converted to anunsigned int. These are called the integer promotions. 48) All other types are unchanged by the integer promotions.