您如何使用C中文件的输入重定向?

问题描述

我是编码的初学者，C是我一直在学习的唯一语言.我已经对输入重定向到文件进行了深入的研究，以试图弄清楚它是如何工作的，但是我不知道在哪里使用命令或确切地如何使用它.我的问题是，我应该在哪里将重定向命令行准确地放在程序中?我知道它看起来像这样:./a< filename.txt，但是我不知道将其放在程序中的什么位置，或者甚至将其放入程序中?我想使用一个简单的循环将文件中的数据读取到scanf中.另外，"a"是您正在编写的C程序的确切名称吗?

I'm very beginner-level in coding, C is the only language I have been learning. I've done thorough research on input redirection to a file to try to figure out how it works, but I do not understand where to use the command or exactly how it is used. My question is, where do I put the redirection command line in the program exactly? I know that it looks something like this: ./a < filename.txt , but I have no idea where to put it in the program, or if it even goes in the program? I want to read data from the files into a scanf using a simple loop. Also, the 'a', is that the exact name of the C program you are writing?

推荐答案

如果要从重定向中读取，则程序需要从中读取stdin:

If you want to read from a redirection, then the program needs to read fromstdin:

int main(void)
{
    char line[1024];

    fgets(line, sizeof line, stdin);

    puts(line);

    return 0;
}

如果您执行这样的程序:

If you execute the program like this:

$ ./readline

然后用户必须输入文本，然后按.

then the user must enter the text and press .

如果您执行这样的程序:

If you execute the program like this:

$ echo "Hello World" | ./readline
Hello World
$ ./readline < filename
First line of filename

然后stdin将被连接到管道/重定向.你不用担心这一点，执行命令的外壳会执行工作(将stdin连接到管道等)，以便您的程序只需要从stdin读取.

then stdin will be connected to the pipe / redirection. You don't have toworry about this, the shell executing the command does the work (connecting stdin to the pipes, etc) so thatyour program only need to read from stdin.

如果您希望用户调用程序，则stdout同样适用并在管道或重定向中使用输出，然后只需正常写入stdout.外壳负责将stdout连接到管道/重定向.

Same thing applies for stdout, if you want that the user calls your programand uses the output in a pipe or redirection, then just write normally tostdout. The shell takes care of connecting stdout to the pipe / redirection.

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