| 类型名称 | 占字节数 | 其他叫法 | 表示的数据范围 | | char | 1 | signed char | -128 ~ 127 | | unsigned char | 1 | none | 0 ~ 255 | | int | 4 | signed int | -2,147,483,648 ~ 2,147,483,647 | | unsigned int | 4 | unsigned | 0 ~ 4,294,967,295 | | short | 2 | short int | -32,768 ~ 32,767 | | unsigned short | 2 | unsigned short int | 0 ~ 65,535 | | long | 4 | long int | -2,147,483,648 ~ 2,147,483,647 | | unsigned long | 4 | unsigned long | 0 ~ 4,294,967,295 | | float | 4 | none | 3.4E +/- 38 (7 digits) | | double | 8 | none | 1.7E +/- 308 (15 digits) | | long double | 10 | none | 1.2E +/- 4932 (19 digits) |
最大值溢出后变为最小值；最小值溢出后变为最大值。
如：
char a=127 a+1为-128
char a=-128 a-1为127
uchar a=255 a+1为0
uchar a=0 a-1 为255
溢出后的数值计算：
上溢： - [max_count]
下溢： +[max_count]
例如：
char a=126 ,则a + 45 =126+45 =172-256 = -85
uchar a = 2 ,则 a - 100 = -98+256 = 158
a,b 基本类型相同时，有符号与无符号数的转换:
无符号a-->有符号b
if(a<max_count/2) b = a
else b = a - [max_count]
有符号数a-->无符号数b
if(a>0) b = a
else b = a + [max_count]
例1 char a = -119 ;uchar b = a;则b = -119 +256 = 137
例2 uchar a = 137 ; char b = a; 则 b = 137 - 256 = -119
例3 signed char chr = 127;
int sum =127;
chr+=10;
sum+=chr;
sum值是
思路 先把chr当成无符号数，chr +=10变成137 然后把chr转化为有符号数137-256 = -119 。-119 + sum (127) = 8.
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