文件中的回车符

时间：2014-04-02 12:21:22

标签： c printf carriage-return

有人可以帮我解决这个谜......？ 我读到了＆＃39; / r＆＃39;和＆＃39; / n＆＃39;，那不是我想问的......

考虑这两个文件：
config.txt： 

home/my_user/Documents/prog/my_folder
home/my_user/Documents/prog/IO/input_for_prog.txt
home/my_user/Documents/prog/IO/correct_output.txt

test.txt： 

This is a test file
Why isn't there carriage return char
at the end of each line in this file?

现在，请考虑以下代码：

int main(int argc, char* argv[]) {

    int fd=open(argv[1], O_RDONLY);
    if (fd==-1) {
        perror("Error opening");
        return -1;
    }

    char ch;
    int ret_code;

    while ((ret_code=read(fd, &ch, 1))!=0) {

        if (ret_code==-1) {
            perror("Error reading");
            return -1;
        }

        printf("Character is: %c, its ascii value: %d\n", ch, ch);
    }
}

暂时忽略潜在的错误，因为这不是问题（我希望）。 此代码只打印文件中的每个字符，并且它的ascii值。

现在，看看我在上面的文件上运行时会发生什么...... 输出 config.txt： 

Character is: h, its ascii value: 104
Character is: o, its ascii value: 111
Character is: m, its ascii value: 109
Character is: e, its ascii value: 101
Character is: /, its ascii value: 47
Character is: m, its ascii value: 109
Character is: y, its ascii value: 121
Character is: _, its ascii value: 95
Character is: u, its ascii value: 117
Character is: s, its ascii value: 115
Character is: e, its ascii value: 101
Character is: r, its ascii value: 114
Character is: /, its ascii value: 47
Character is: D, its ascii value: 68
Character is: o, its ascii value: 111
Character is: c, its ascii value: 99
Character is: u, its ascii value: 117
Character is: m, its ascii value: 109
Character is: e, its ascii value: 101
Character is: n, its ascii value: 110
Character is: t, its ascii value: 116
Character is: s, its ascii value: 115
Character is: /, its ascii value: 47
Character is: p, its ascii value: 112
Character is: r, its ascii value: 114
Character is: o, its ascii value: 111
Character is: g, its ascii value: 103
Character is: /, its ascii value: 47
Character is: m, its ascii value: 109
Character is: y, its ascii value: 121
Character is: _, its ascii value: 95
Character is: f, its ascii value: 102
Character is: o, its ascii value: 111
Character is: l, its ascii value: 108
Character is: d, its ascii value: 100
Character is: e, its ascii value: 101
Character is: r, its ascii value: 114
, its ascii value: 13
Character is: 
, its ascii value: 10
Character is: h, its ascii value: 104
Character is: o, its ascii value: 111
Character is: m, its ascii value: 109
Character is: e, its ascii value: 101
Character is: /, its ascii value: 47
Character is: m, its ascii value: 109
Character is: y, its ascii value: 121
Character is: _, its ascii value: 95
Character is: u, its ascii value: 117
Character is: s, its ascii value: 115
Character is: e, its ascii value: 101
Character is: r, its ascii value: 114
Character is: /, its ascii value: 47
Character is: D, its ascii value: 68
Character is: o, its ascii value: 111
Character is: c, its ascii value: 99
Character is: u, its ascii value: 117
Character is: m, its ascii value: 109
Character is: e, its ascii value: 101
Character is: n, its ascii value: 110
Character is: t, its ascii value: 116
Character is: s, its ascii value: 115
Character is: /, its ascii value: 47
Character is: p, its ascii value: 112
Character is: r, its ascii value: 114
Character is: o, its ascii value: 111
Character is: g, its ascii value: 103
Character is: /, its ascii value: 47
Character is: I, its ascii value: 73
Character is: O, its ascii value: 79
Character is: /, its ascii value: 47
Character is: i, its ascii value: 105
Character is: n, its ascii value: 110
Character is: p, its ascii value: 112
Character is: u, its ascii value: 117
Character is: t, its ascii value: 116
Character is: _, its ascii value: 95
Character is: f, its ascii value: 102
Character is: o, its ascii value: 111
Character is: r, its ascii value: 114
Character is: _, its ascii value: 95
Character is: p, its ascii value: 112
Character is: r, its ascii value: 114
Character is: o, its ascii value: 111
Character is: g, its ascii value: 103
Character is: ., its ascii value: 46
Character is: t, its ascii value: 116
Character is: x, its ascii value: 120
Character is: t, its ascii value: 116
, its ascii value: 13
Character is: 
, its ascii value: 10
Character is: h, its ascii value: 104
Character is: o, its ascii value: 111
Character is: m, its ascii value: 109
Character is: e, its ascii value: 101
Character is: /, its ascii value: 47
Character is: m, its ascii value: 109
Character is: y, its ascii value: 121
Character is: _, its ascii value: 95
Character is: u, its ascii value: 117
Character is: s, its ascii value: 115
Character is: e, its ascii value: 101
Character is: r, its ascii value: 114
Character is: /, its ascii value: 47
Character is: D, its ascii value: 68
Character is: o, its ascii value: 111
Character is: c, its ascii value: 99
Character is: u, its ascii value: 117
Character is: m, its ascii value: 109
Character is: e, its ascii value: 101
Character is: n, its ascii value: 110
Character is: t, its ascii value: 116
Character is: s, its ascii value: 115
Character is: /, its ascii value: 47
Character is: p, its ascii value: 112
Character is: r, its ascii value: 114
Character is: o, its ascii value: 111
Character is: g, its ascii value: 103
Character is: /, its ascii value: 47
Character is: I, its ascii value: 73
Character is: O, its ascii value: 79
Character is: /, its ascii value: 47
Character is: c, its ascii value: 99
Character is: o, its ascii value: 111
Character is: r, its ascii value: 114
Character is: r, its ascii value: 114
Character is: e, its ascii value: 101
Character is: c, its ascii value: 99
Character is: t, its ascii value: 116
Character is: _, its ascii value: 95
Character is: o, its ascii value: 111
Character is: u, its ascii value: 117
Character is: t, its ascii value: 116
Character is: p, its ascii value: 112
Character is: u, its ascii value: 117
Character is: t, its ascii value: 116
Character is: ., its ascii value: 46
Character is: t, its ascii value: 116
Character is: x, its ascii value: 120
Character is: t, its ascii value: 116
, its ascii value: 13
Character is: 
, its ascii value: 10

输出 test.txt： 

Character is: T, its ascii value: 84
Character is: h, its ascii value: 104
Character is: i, its ascii value: 105
Character is: s, its ascii value: 115
Character is:  , its ascii value: 32
Character is: i, its ascii value: 105
Character is: s, its ascii value: 115
Character is:  , its ascii value: 32
Character is: a, its ascii value: 97
Character is:  , its ascii value: 32
Character is: t, its ascii value: 116
Character is: e, its ascii value: 101
Character is: s, its ascii value: 115
Character is: t, its ascii value: 116
Character is:  , its ascii value: 32
Character is: f, its ascii value: 102
Character is: i, its ascii value: 105
Character is: l, its ascii value: 108
Character is: e, its ascii value: 101
Character is: 
, its ascii value: 10
Character is: W, its ascii value: 87
Character is: h, its ascii value: 104
Character is: y, its ascii value: 121
Character is:  , its ascii value: 32
Character is: i, its ascii value: 105
Character is: s, its ascii value: 115
Character is: n, its ascii value: 110
Character is: ', its ascii value: 39
Character is: t, its ascii value: 116
Character is:  , its ascii value: 32
Character is: t, its ascii value: 116
Character is: h, its ascii value: 104
Character is: e, its ascii value: 101
Character is: r, its ascii value: 114
Character is: e, its ascii value: 101
Character is:  , its ascii value: 32
Character is: c, its ascii value: 99
Character is: a, its ascii value: 97
Character is: r, its ascii value: 114
Character is: r, its ascii value: 114
Character is: i, its ascii value: 105
Character is: a, its ascii value: 97
Character is: g, its ascii value: 103
Character is: e, its ascii value: 101
Character is:  , its ascii value: 32
Character is: r, its ascii value: 114
Character is: e, its ascii value: 101
Character is: t, its ascii value: 116
Character is: u, its ascii value: 117
Character is: r, its ascii value: 114
Character is: n, its ascii value: 110
Character is:  , its ascii value: 32
Character is: c, its ascii value: 99
Character is: h, its ascii value: 104
Character is: a, its ascii value: 97
Character is: r, its ascii value: 114
Character is: 
, its ascii value: 10
Character is: a, its ascii value: 97
Character is: t, its ascii value: 116
Character is:  , its ascii value: 32
Character is: t, its ascii value: 116
Character is: h, its ascii value: 104
Character is: e, its ascii value: 101
Character is:  , its ascii value: 32
Character is: e, its ascii value: 101
Character is: n, its ascii value: 110
Character is: d, its ascii value: 100
Character is:  , its ascii value: 32
Character is: o, its ascii value: 111
Character is: f, its ascii value: 102
Character is:  , its ascii value: 32
Character is: e, its ascii value: 101
Character is: a, its ascii value: 97
Character is: c, its ascii value: 99
Character is: h, its ascii value: 104
Character is:  , its ascii value: 32
Character is: l, its ascii value: 108
Character is: i, its ascii value: 105
Character is: n, its ascii value: 110
Character is: e, its ascii value: 101
Character is:  , its ascii value: 32
Character is: i, its ascii value: 105
Character is: n, its ascii value: 110
Character is:  , its ascii value: 32
Character is: t, its ascii value: 116
Character is: h, its ascii value: 104
Character is: i, its ascii value: 105
Character is: s, its ascii value: 115
Character is:  , its ascii value: 32
Character is: f, its ascii value: 102
Character is: i, its ascii value: 105
Character is: l, its ascii value: 108
Character is: e, its ascii value: 101
Character is: ?, its ascii value: 63
Character is: 
, its ascii value: 10

我注意到的一些事情，无法找到答案：
首先，正如 test.txt 文件所示，为什么没有＆＃39; / r＆＃39;烧焦 在此文件的每一行的末尾，而在 config.txt 中，有两个＆＃39; / r＆＃39; 和＆＃39; / n＆＃39;在每一行的末尾??
其次，为什么单词＆＃34;字符是＆＃34;消失在打印＆＃34;的行，其ascii值为13＆＃34; ??

感谢。

5 个答案:

答案 0 :(得分：5)

当打印到控制台窗口（即不是文件）时，\r指示它返回到行的开头（因此“Character is”文本消失）。但是，\n会指示它进入下一行。例如，\r对于在同一行显示进度非常有用。

可以使用\r\n，\n或每行末尾的\r保存文件（请参阅下面的评论），这些日子通过文字解释相同 - 编辑（事实上，如果你混合文件中的类型，很多人会警告你）。您可能会看到一个文件包含\r\n而另一个文件只包含\n。

答案 1 :(得分：2)

行结束差异可能由各种原因引起，例如：使用不同的文本编辑器。

对于\n和\r字符，他们会执行以下操作：

  • \n将插入符号移至下一行
  • \r将插入符移动到当前行的开头

有了这些知识，你应该能够理解程序的输出。这是正常的＆＃39;字符：

Character is: t, its ascii value: 116

这是\r，请注意插入符号在打印时如何移动到行的开头：

, its ascii value: 13

这是\n，请注意插入符号在打印后如何移动到下一行：

Character is: 
, its ascii value: 10

答案 2 :(得分：1)

原因＆＃34;字符是＆＃34;消失的是\ 13字符是回车。它将光标放回到行的开头，以便文本的其余部分＆＃34;，其ascii值为......＆＃34;覆盖它。

只有\ n（新行）或\ r \ n（回车符和新行）才有效。

答案 3 :(得分：1)

第一个问题是我们无法解决的，因为我们不知道文件是如何创建的。 Windows程序通常使用'\ r \ n'而Linux'\ n'就足够了。

第二个问题很容易回答，你打印“字符是：\ n，它的......”所以你得到一个换行符。除非您转义特殊字符，否则无法在不获取换行符的情况下打印换行符。

编辑你可能想逃避更多\ r＆amp; \ n，像标签和其他人一样。见here

答案 4 :(得分：0)

我无法回答这两个文件之间的差异，因为我没有这些文件，也没有办法创建它们。

话虽如此，ASCII值13和ASCII值10是不可打印的字符。这意味着，除非您从用于控制回车和/或换行到\r或\n的看似不可见的字符中检测并转换该值，否则您将无法访问＆ ＃34;参见＆＃34;它

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