I know there is some question about this already, but I don't understand what I'm doing wrong here. I'm reading numbers from file, and storing them into array. Now I want to create process that the parent is reading 10 numbers, then the children read the other numbers, add them together and send to the parent process, but for some reason the return value I'm getting is wrong. what I'm missing here? I added image to demonstrate

#include <stdio.h>
#include <stdlib.h>
#include <malloc.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <unistd.h>

int my_read(char *arg1);

int main(int argc, char *argv[])
{
  my_read("numbers.txt");
}

int my_read(char *arg1)
{
  int status;
  int avg = 0;
  int p, i;
  int arr[26];

  FILE *file = fopen(arg1, "r");

  if (NULL == file)
  {
    printf("file can't be opened \n");
  }

  fscanf(file, "%d", &i);
  while (!feof(file))
  {
    arr[p] = i;
    p  ;
    fscanf(file, "%d", &i);
  }
  arr[25] = i;

  // fork
  printf("I am the parent: %d\n", (int)getpid());

  pid_t pid = fork();

  if (pid < 0)
  { /* error occurred */
    perror("Fork failed");
  }
  if (pid == 0)
  { /* child process */
    printf("I am the child with pid %d\n", (int)getpid());
    for (i = 10; i < 26; i  )
    {
      printf("%d\n", arr[i]);
      avg  = arr[i];
    }
    exit(avg);//send to parent
    
  }

  /* parent process */

  for (i = 0; i < 10; i  )
  {
    printf("%d\n", arr[i]);
  }

  wait(&status);
  printf("I am the parent: %d\n", (int)getpid());
  printf("%d\n", status);

  fclose(file);
  return (0);
}

CodePudding user response：

This code deals with most of the problems outlined in my comments. One area it addresses that wasn't highlighted in the comments is the fragility of the original code — it assumes that there will be exactly 26 numbers in the file. This code ensures that only 26 numbers are read.

#include <stdio.h>
#include <stdlib.h>
#include <sys/wait.h>
#include <unistd.h>

int my_read(char *arg1);

int main(void)
{
  my_read("numbers.txt");
  return 0;
}

int my_read(char *arg1)
{
  int status;
  int avg = 0;
  int p, i;
  int arr[26];

  FILE *file = fopen(arg1, "r");

  if (NULL == file)
  {
    fprintf(stderr, "file '%s' can't be opened for reading\n", arg1);
    exit(EXIT_FAILURE);
  }

  p = 0;
  while (fscanf(file, "%d", &i) == 1 && p < 26)
    arr[p  ] = i;

  fclose(file);

  /* p contains the number of values */

  // fork
  printf("I am the parent: %d\n", (int)getpid());

  pid_t pid = fork();

  if (pid < 0)
  { /* error occurred */
    perror("Fork failed");
  }
  if (pid == 0)
  { /* child process */
    printf("I am the child with pid %d\n", (int)getpid());
    for (i = 10; i < p; i  )
    {
      printf("%d\n", arr[i]);
      avg  = arr[i];
    }
    printf("Sum of values: %d\n", avg);
    avg /= (26 - 10);
    printf("Avg of values: %d (0x%.2X)\n", avg, avg);
    exit(avg);//send to parent
  }

  /* parent process */

  for (i = 0; i < 10; i  )
  {
    printf("%d\n", arr[i]);
  }

  wait(&status);
  printf("I am the parent: %d\n", (int)getpid());
  printf("Raw: 0x%.4X\n", status);
  printf("Value: %d\n", WEXITSTATUS(status));

  return (0);
}

Given the input file (with 4 extra primes):

1 2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97
101 103 107 109

it still works correctly — and produces output such as:

I am the parent: 18797
1
2
3
5
7
11
13
17
19
23
I am the child with pid 18798
29
31
37
41
43
47
53
59
61
67
71
73
79
83
89
97
Sum of values: 960
Avg of values: 60 (0x3C)
I am the parent: 18797
Raw: 0x3C00
Value: 60

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