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There is a task: Write a program to calculate the sum of matrix elements. The matrix is entered from a file. The calculation of the sums of the elements of each row is performed in separate processes. To transfer data to the parent process, use the named pipe mechanism (FIFO).

I found this solution, however it does not meet all the requirements:

#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
 
 
using namespace std;
 
 
 
int main(){
    int fd[2];
    int i,j;
    int p[2];
    int arr[2][2];
    int marr[2];
    FILE *file = fopen("matrix","r");
    if (!file)
        printf("NO FILE");
    for(i = 0; i < 2; i++){
        for(j = 0; j < 2; j++){
            fscanf(file, "%d", &arr[i][j]);
            printf("%d ", arr[i][j]);
        }
        printf("\n");
    }
 
    if(pipe(fd) < 0) {
        printf("Pipe error!\n");
        return 1;
    }
    int max=arr[0][0];
 
    for (int i=0; i<2; i+=1){
        p[i]=fork();
        if(p[i]==0){
        printf("%d subprocess\n", i);
        max=arr[i][0];
            for(j=0; j<2; j++){
                if(max<arr[i][j]){
                    max=arr[i][j];
                    }
                }
            close(fd[0]);
        printf("write to pipe: max=%d i=%d\n", max, i);
            write(fd[1],&max,sizeof(int));
            write(fd[1],&i,sizeof(int));
            exit(0);
        }
        else{
           
        }
    }
 close(fd[1]);
            for(int k=0; k<2; k++){
                read(fd[0],&max,sizeof(int));
                read(fd[0],&i,sizeof(int));
        printf("read from pipe: max=%d i=%d\n", max, i);
                marr[i]=max;
            }
   printf("massiv max:\n");
    for(i=0; i<2; i++){
        printf("%d\n",marr[i]);
    }
    fclose(file);
    return 0;
}

I tried to somehow change the relationship between the processes from pipe to fifo, but I can't check, because the code needs to be run on a linux virtual machine, and in QT the SIGSEGV error appears on the line

fscanf(file, "%d", &arr[i][j]);

, the reasons for which, as I understand it, can be very different.

The test file for this code will look like:

3 4

5 6

and it finds the maximum of each row. It won't be difficult for me to redo it for my task, the main problem is in fifo. I will be grateful for any hints.

Saveliy Adaev
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  • A pipe is a FIFO. – Eric Postpischil Oct 26 '22 at 12:09
  • That is C++ code, not C. Why did you tag C and show C++ code? Is your project requirement for C or C++? Are you going to change the C++ code to C? – Eric Postpischil Oct 26 '22 at 12:09
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    Re “I found this solution”: You are supposed to do coursework by writing code, not by finding it. – Eric Postpischil Oct 26 '22 at 12:11
  • Re “the SIGSEGV error appears”: Test the result of `fopen`. If it is a null pointer, use `perror` to print the reason why `fopen` did not open the file. – Eric Postpischil Oct 26 '22 at 12:14
  • Okay, will try that. So, you are saying that given code is already using fifo? There is no mkfifo command though. I find it difficult to write something i don't know anything about yet, so i look for proper examples of my task, and i said that i will redo the whle thing by myself anyway. Sorry about the tag, my mistake. – Saveliy Adaev Oct 26 '22 at 12:36
  • A “pipe” is a software construct that is a “FIFO.” In this sense, a FIFO is a data structure and associated interface that provides first-in first-out storage of data. A “fifo” as made with `mkfifo` is a different software construct, also called a “named pipe” that is also a FIFO. If the assignment is to use a FIFO, then an unnamed pipe made with `pipe` is a FIFO. If the assignment is to use a Unix fifo file, then you need to use `mkfifo`. – Eric Postpischil Oct 26 '22 at 13:30

0 Answers0