文件中的回车字符

Question

有人能帮我解开这个谜团吗？

我读到了'/r‘和'/n’之间的区别，这不是我想要问的.

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，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);
    }
}

请暂时忽略潜在的bug，因为这不是问题所在(我希望如此)。这段代码将只打印文件中的每个字符，并且它是ascii值。

现在，看看当我在上面的文件上运行时会发生什么.

config.txt:的输出

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

test.txt:的输出

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

有几件事我注意到了，却找不到答案：

首先，正如test.txt文件所建议的，为什么这个文件的每一行末尾没有'/r‘字符，而在config.txt中，每一行末尾都有'/r’和‘/n？

第二，为什么“字符”在打印的行处消失，其ascii值为13"？“

谢谢。

Answer 1

当打印到控制台窗口(即不是文件)时，\r指示它返回行的开头(因此“字符是”文本消失)。然而，\n指示它转到下一行。例如，\r对于显示同一行的进度非常有用。

文件可以在每一行末尾用\r\n、\n或\r保存(请参阅下面的注释)，而现在文本编辑器也会对文件进行相同的解释(实际上，如果将文件中的类型混合在一起，许多人会警告您)。看起来您有一个带有\r\n的文件，另一个文件只有\n。

Answer 2

行尾差异可能是由各种原因造成的，例如使用不同的文本编辑器。

对于\n和\r字符，它们执行以下操作：

• \n将插入符号移动到下一行
• \r将插入符号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”的性格：

Character is: t, its ascii value: 116

这是\r，注意打印时插入符号是如何移动到行的开头的：

, its ascii value: 13

这是\n，注意打印时插入符号是如何移动到下一行的：

Character is: 
, its ascii value: 10

Answer 3

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’，而对于Linux '\n‘则足够了。

第二个问题很容易回答，你可以打印“字符是：\n，它的.”所以你可以换一条新线路。除非您转义特殊字符，否则无法打印换行符。

编辑您可能想要转义更多的\r &n，像制表符和其他。请参阅这里