公式溢出計算過程
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上溢: - [max_count]
下溢: +[max_count]
例如:
char a=126 ,則a + 45 =126+45 =172-256 = -85
uchar a = 2 ,則 a - 100 = -98+256 = 158
a,b 基本類型相同時,有符號與無符號數的轉換:
無符號a-->有符號b
if(a<max_count/2) b = a
else b = a - [max_count]
有符號數a-->無符號數b
if(a>0) b = a
else b = a + [max_count]
例1 char a = -119 uchar b = a則b = -119 +256 = 137
例2 uchar a = 137 char b = a 則 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當成無符號數,chr +=10變成137 然後把chr轉化為有符號數137-256 = -119 。-119 + sum (127) = 8.