問題描述
在 C/C++ 中，unsigned char 用于什么?它與普通的 char 有何不同?
In C/C++, what an unsigned char is used for? How is it different from a regular char?
推薦答案
在 C++ 中，有三種不同的字符類型:
In C++, there are three distinct character types:
char有符號的字符無符號字符
如果您為 text 使用字符類型，請使用不合格的 char:
If you are using character types for text, use the unqualified char:
- 它是字符文字的類型，如
'a'或'0'(僅在 C++ 中，在 C 中它們的類型是int) - 它是組成C字符串的類型，如
"abcde"
- it is the type of character literals like
'a'or'0'(in C++ only, in C their type isint) - it is the type that makes up C strings like
"abcde"
它也可以作為數字值計算，但未指定該值是被視為有符號還是無符號.當心通過不等式進行字符比較 - 盡管如果您將自己限制為 ASCII (0-127)，那么您就很安全了.
It also works out as a number value, but it is unspecified whether that value is treated as signed or unsigned. Beware character comparisons through inequalities - although if you limit yourself to ASCII (0-127) you're just about safe.
如果您將字符類型用作數字，請使用:
If you are using character types as numbers, use:
signed char，它給你至少 -127 到 127 的范圍.(-128 到 127 很常見)unsigned char，它給你至少 0 到 255 的范圍.
signed char, which gives you at least the -127 to 127 range. (-128 to 127 is common)unsigned char, which gives you at least the 0 to 255 range.
至少"，因為 C++ 標準只給出了每個數字類型需要覆蓋的最小范圍的值.sizeof (char) 需要為 1(即一個字節)，但理論上一個字節可以是例如 32 位.sizeof 仍會報告其大小為 1 - 這意味著您可以有 sizeof (char)== sizeof (long) == 1.
"At least", because the C++ standard only gives the minimum range of values that each numeric type is required to cover. sizeof (char) is required to be 1 (i.e. one byte), but a byte could in theory be for example 32 bits. sizeof would still be report its size as 1 - meaning that you could have sizeof (char) == sizeof (long) == 1.
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