使用int作为字符类型与EOF进行比较时 [英] Using int for character types when comparing with EOF
问题描述
从Kernighan和Ritchie的C程序设计语言第16页引用 -
Quoting from Kernighan and Ritchie's 'The C Programming Language' Page 16 -
#include<stdio.h>
main()
{
int c;
c = getchar();
while(c!=EOF)
{
putchar(c);
c = getchar();
}
getchar();
return 0;
}
的类型字符专指用于存储这样的字符数据，但可以使用任何整数类型。我们使用 INT 的微妙而重要的原因。现在的问题是区分有效数据输入的结束。解决的办法是，的getchar 时，有没有更多的返回独特价值输入时，不能与任何真实人物相混淆一个值，该值被称为 EOF ，为文件结束，我们必须声明 C 是一个类型足够大，认为的getchar 的回报。我们不能用任何值字符，因为> C EOF 除了任何可能的字符。因此，我们使用 INT 。
"The type char is specifically meant for storing such character data, but any integer type can be used. We used int for a subtle but important reason. The problem is distinguishing the end of the input from valid data. The solution is that getchar returns a distinctive value when there is no more input, a value that cannot be confused with any real character. This value is called EOF, for "end of file". We must declare c to be a type big enough to hold any value that getchar returns. We can't use char since c must be big enough to hold EOF in addition to any possible char. Therefore we use int.".
我在stdio.h抬头一看，上面写着的#define EOF（-1）
I looked up in stdio.h, it says #define EOF (-1)
这本书得出结论称字符不能使用，而这一计划工作得很好（请参阅编辑）与 C 为字符数据类型为好。到底是怎么回事？在位，并签署价值方面任何人都可以解释一下吗？
The book conclusively states that char cannot be used whereas this program "works just fine" (See EDIT) with c as char data type as well. What is going on? Can anyone explain in terms of bits and signed values?
编辑：结果
由于奥利奇在答复中提到，该计划不能 EOF 和 255 区分。所以它不会正常工作。我想知道发生了什么 - 你是说，当我们做比较，C = EOF，EOF的值将被强制转换为字符值= 255（11111111二进制;！即位0 EOF的7写成2的补时符号）？
As Oli mentioned in the answer, the program cannot distinguish between EOF and 255. So it will not work fine. I want to know what's happening - Are you saying that when we do the comparison c!=EOF, the EOF value gets cast to a char value = 255 (11111111 in binary; i.e. the bits 0 through 7 of EOF when written in 2's complement notation)?
推荐答案
您程序不做工精细;这将无法 EOF 和 255 。
Your program doesn't work fine; it won't be able to distinguish between EOF and 255.
它似乎正常工作的原因是因为字符大概是签署你的平台上，因此它仍然能够再presenting 1 的
The reason it appears to work correctly is because char is probably signed on your platform, so it's still capable of representing -1.
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