为什么此C程序在输出中输出奇怪的字符?

问题描述

我有以下程序:

#include <stdio.h>

int main()
{
        int ch;
        while( ch = getchar() != '\n') {
                printf("Read %c\n",ch);
        }
        return 0;
}

无论我输入什么，我都会得到:

No matter what I enter I get:

Read

为什么会这样?我看到的是什么奇怪的字符?

Why is this happening and what is that weird char that I see?

Stackoverflow没有打印出奇怪的字符.您可以在这里看到它: http://ideone.com/EfZHr

Stackoverflow is not printing the weird char. You can see it here: http://ideone.com/EfZHr

推荐答案

您需要将括号放置为:

while( (ch = getchar()) != '\n')

的

优先级 大于=

while( ch = getchar() != '\n')

与:

while( ch = (getchar() != '\n') )

读取char的

将其与换行符进行比较，然后将比较结果分配给ch.现在比较的结果是0(输入换行符时)或1(输入其他任何内容时)

which reads a char compares it with newline and then assigns the result of comparison to ch. Now the result of comparison is 0 (when newline is entered) or 1 (when anything else is entered)

您看到的奇怪字符是 控制字符 的值为1，没有ASCII 1的可打印符号，因此我猜想它是在其中打印出值为0001的奇怪字符的shell.

The weird char you're seeing is the control char with value 1, there is no printable symbol for ASCII 1, so I guess its the shell that prints the weird char with value 0001 in it.

您可以通过将程序输出管道传输到八进制转储(od)来确认:

You can confirm it by piping your program output to octal dump (od) :

$ echo 'a' | ./a.out | od -bc         # user entered 'a'
0000000 122 145 141 144 040 001 012
          R   e   a   d     001  \n
here you go  ----------------^


$ echo '\n' | ./a.out | od -bc        # user entered '\n'
0000000

与-Wall一起使用时的GCC警告您:

GCC when used with -Wall warns you as:

warning: suggest parentheses around assignment used as truth value

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