如何在C（STDIN）中扫描重定向文件？

Question

Say I'm calling a program:

$ ./dataset < filename

where filename is any file with x amount of line pairs where the first line contains a string and second line contains 10 numbers separated by spaces. The last line ends with "END"

How can I then start putting the first lines of pairs (string) into:

char *experiments[20] // max of 20 pairs

and the second lines of the pairs (numbers) into:

int data[10][20] // max of 20, 10 integers each

Any guidance? I don't even understand how I'm supposed to scan the file into my arrays.

Update:

So say this is my file:

Test One  
0 1 2 3 4 5 6 7 8 9  
END

Then redirecting this file would mean if I want to put the first line into my *experiments, that I would need to scan it as such?

scanf("%s", *experiments[0]);

Doing so gives me an error: Segmentation fault (core dumped)

What is incorrect about this?

Say my file is simply numbers, for ex:

0 1 2 3 4 5 6 7 8 9

Then,
scanf("%d", data[0][0]); works, and will hold value of '1'. Is there an easier way to do this for the whole line of data? ie data[0-9][0] .

Answer 1

The redirected file is associated with the FILE * stdin . It's already opened for you...

otherwise, you can treat it the same as any other text file, and/or use the functions that are dedicated to standard input - with the only exception that you cannot seek in the file and not retrieve the size of the input.

Answer 2

find the pseudo-code, code explains how to read the input

int main()
{ 

    char str[100]; // make sure that this size is enough to hold the single line
    int no_line=1;

    while(gets(str) != NULL && strcmp(str,"END"))
    {    
            if(no_line % 2 == 0)
            {
                /*read integer values from the string "str" using sscanf, sscanf can be called in a loop with %d untill it fails */   
            }  
            else
            {
                /*strore string in your variable "experiments" , before copying allocate a memory for the each entry */ 
            }
         no_line++;
    }
 }

Answer 3

For the data sizes you're talking about, by far the easiest thing to do is just slurp all of the content into a buffer and work on that: you don't have to be super-stingy, just make sure that you don't overrun.

If you want to be super-stingy with memory, preallocate a 4kB buffer with malloc() , progressively read() into it from stdin , and realloc() another 4kB every time the input exceeds what you've already read. If you don't care so much about being stingy with memory (eg on a modern machine with gigabytes of memory), just malloc() something much bigger than the expected input (eg a megabyte) and bug out if the input is more than that: this is far simpler to implement but less general/elegant.

You then have all of the input in a buffer and you can do what you like with it, which depends too strongly on the format of the input for me to say how you should approach that part.