将Cat命令与C代码一起使用

Question

I'm using the cat command for a school project.

What i need is to give a txt file as input to my code and then evaluate the output (saved in a txt file). So far i'm using this in my command line:

cat input_000.txt | ./main > my_output.txt

Where ./main is my C code.

The input_000.txt is structured like this:

0 a a R 3
1 a b L 4
4 c b R 1
ecc...

I have a certain number of lines made of 5 characters (with spaces between them).

How do i get the content of each line in my C code? I've been told so use standard input, but i've always used scanf only from keyboard input.

Does it still work in this case?

And how should i save my output? I usually use fwrite , but in this case is everything managed by the cat command

Answer 1

That's how pipes works, it sets up so the output of the left-hand side of the pipe will be written to standard input for the right-hand side program.

In short if you can read input from stdin (like you do with plain scanf ) then you won't have to do any changes at all.

Redirection works just about the same. Redirecting to a file ( > ) will make all writes to stdout go to the file. Redirecting from a file ( < ) will make all reads from stdin come from the file.

Answer 2

您可以使用getline（或scanf ）读取stdin （fd = 0）并将其保存在C代码中的char*中……然后，您只需要编写stdout （fd = 1），然后>做好写在文件中的工作

Answer 3

What you need is something like this inside your function...

FILE *input = fopen("input.txt","rw"); //rw (read-write)
FILE *output= fopen("output.txt","rw"); //rw (read-write)
char inputArray[500];
char outputArray[500];

while(fscanf(input,"%s", inputArray) != EOF){
      //read the line and save in 'inputArray'
      //you can also use %c to find each caracter, in your case I think it's better...you can //save each caracter in a array position, or something like that
}

while(number of lines you need or the number of lines from your input file){
      fprintf(output,"%s\n",output); //this will write the string saved in 'outputArray'
}

If you don't want to use it...then you can give your main.c the input using < and saving the output >

./main.o < input.txt > output.txt

(something like that, its not safer because the terminal could have the settings to use other type of charset...