为什么getchar函数（）承认EOF只在一行的开始？ [英] Why does getchar() recognize EOF only in the beginning of a line?

问题描述

这个例子是从K＆放大器; R书

This example is from the K&R book

#include<stdio.h>


main()
{
    long nc;

    nc = 0;
    while(getchar() != EOF)
        ++nc;
    printf("%ld\n", nc);
}

你能解释我为什么它工作的方式。谢谢你。

Could you explain me why it works that way. Thanks.

^ Z ^ Z无法正常工作或（除非它是在一行的开头）

^Z^Z doesn't work either (unless it's in the beginning of a line)

推荐答案

传统UNIX的tty间pretation EOF 字符是使阻塞阅读无论是煮熟的TTY行缓冲区内的缓冲后读的回报。在新线的起点，它意味着读返回0（读数为零字节），并且顺便提一句，0尺寸读是怎么检测的文件条件对普通文件的结尾。

Traditional UNIX interpretation of tty EOF character is to make blocking read return after reading whatever is buffered inside a cooked tty line buffer. In the start of a new line, it means read returning 0 (reading zero bytes), and incidentally, 0-sized read is how the end of file condition on ordinary files is detected.

这就是为什么的第一个的 EOF 在一行的中间只是强制行的开头是阅读，不做C运行时库检测文件的结束。的两个的 EOF 成一排字符产生0大小的读，因为第二个强制空缓冲区为读提出的申请。

That's why the first EOF in the middle of a line just forces the beginning of the line to be read, not making C runtime library detect an end of file. Two EOF characters in a row produce 0-sized read, because the second one forces an empty buffer to be read by an application.

$ cat
foo[press ^D]foo <=== after ^D, input printed back before EOL, despite cooked mode. No EOF detected
foo[press ^D]foo[press ^D] <=== after first ^D, input printed back, and on second ^D, cat detects EOF

$ cat
Some first line<CR> <=== input
Some first line <=== the line is read and printed
[press ^D] <=== at line start, ^D forces 0-sized read to happen, cat detects EOF

我假设你的C运行时库模仿上面（有没有特殊的处理描述语义 ^ Z 在水平 KERNEL32 电话，更不用说系统调用，在Windows上）。这就是为什么它可能会检测后EOF ^ Z ^ Z 即使在输入线的中间。

I assume that your C runtime library imitates the semantics described above (there is no special handling of ^Z at the level of kernel32 calls, let alone system calls, on Windows). That's why it would probably detect EOF after ^Z^Z even in the middle of an input line.

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