char的范围究竟是多少。
百度百科里面讲
char是C/C++整型数据中比较古怪的一个，其它的如int/long/short等不指定signed/unsigned时都默认是signed，但char在标准中是unsigned，编译器可以实现为带符号的，也可以实现为不带符号的，有些编译器如pSOS的编译器，还可以通过编译开关来指定它是有符号数还是无符号数。
但是看过一本书说
char的范围是0-127
signed char的范围是-127到127
unsigned char的范围是0-255
char的范围不是应该是和unsigned char的范围一样都是0-127
[解决办法]
5.2.4.2.1
If the value of an object of type char is treated as a signed integer when used in an
expression, the value of CHAR_MIN shall be the same as that of SCHAR_MIN and the
value of CHAR_MAX shall be the same as that of SCHAR_MAX. Otherwise, the value of
CHAR_MIN shall be 0 and the value of CHAR_MAX shall be the same as that of
UCHAR_MAX.15) The value UCHAR_MAX shall equal 2^CHAR_BIT - 1.
J.3.4 Implementation-defined behavior:
Which of signed char or unsigned char has the same range, representation,
and behavior as ‘‘plain’’ char (6.2.5, 6.3.1.1).
