I am reading from the user the size of an arr. I create the arr[row][col] and fill it with random integers. Then i want to send each row from the parent process to the child so i create a new arr2 to store every time the current row in it. I read the arr2 to child process and calculating the sum of the row. At the end i want to send the sum to parent process and print it. I do this in a for(i=0;i<row;i ). The problem is that the child process only takes the first row every time.
#include <sys/types.h>
#include<stdio.h>
#include <unistd.h>
#include<time.h>
#include<stdlib.h>
int main(){
int gram, steiles;
printf("Dwse mou tis grammes tou pinaka\n");
scanf("%d", &gram);
printf("Dwse mou tis steiles tou pinaka\n");
scanf("%d", &steiles);
int arr[gram][steiles];
int arr2[gram];
srand(time(NULL));
for (int i = 0; i < gram; i ) {
for (int j = 0; j < steiles; j ) {
arr[i][j] = rand() % 20 1;
}
}
for (int i = 0; i < gram; i ) {
for (int j = 0; j < steiles; j ) {
printf("%d", arr[i][j]);
printf("\t");
}
printf("\n");
}
pid_t pid;
int fd[2], fd1[2], sum=0;
if (pipe(fd) == -1) {
return 2;
}
if (pipe(fd1) == -1) {
return 3;
}
for (int i = 0; i < gram; i ) {
pid = fork();
if (pid<0) {
return 1;
}
if (pid>0){
for (int j = 0; j < steiles; j ) {
arr2[j]=arr[i][j];
}
close(fd[0]);
write(fd[1], arr2, sizeof(int)*steiles);
close(fd[1]);
close(fd1[1]);
read(fd1[0], &sum, sizeof(int));
close(fd1[0]);
printf("the sum of the row is: %d", sum);
}else{
wait(NULL);
close(fd[1]);
read(fd[0], arr2, sizeof(int)* steiles);
close(fd[0]);
for (int k = 0; k < steiles; k ) {
// printf("%d\t", arr2[k]);
sum =arr2[k];
}
close(fd1[0]);
write(fd1[1], &sum, sizeof(int));
close(fd1[1]);
}
}
}
CodePudding user response：
I've outlined many of the problems in the comments above, including:
- You don't error check your I/O calls but should.
- The parent process closes the pipes for the first child; the second and subsequent children don't stand a chance, poor things. They've been deprived of all communication with the parent, and you know how much children benefit from talking with their parents.
- Create the pipes inside the loop, not outside. Note that error checking the I/O calls would have told you about this problem.
- Don't forget to end messages with newlines.
- Also, make sure your child processes exit after they've done their stuff. As it stands, the first child reads its data, and then goes back around the loop to run a new child (as well as the parent running a new child).
Here's some code which still skips on the I/O error checking but works correctly:
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <unistd.h>
static void dump_vector(const char *tag, size_t size, const int *data);
int main(void)
{
int gram, steiles;
printf("Dwse mou tis grammes tou pinaka\n");
scanf("%d", &gram);
printf("Dwse mou tis steiles tou pinaka\n");
scanf("%d", &steiles);
int arr[gram][steiles];
int arr2[gram];
srand(time(NULL));
for (int i = 0; i < gram; i )
{
for (int j = 0; j < steiles; j )
{
arr[i][j] = rand() % 20 1;
}
}
for (int i = 0; i < gram; i )
{
for (int j = 0; j < steiles; j )
{
printf("%d", arr[i][j]);
printf("\t");
}
printf("\n");
}
for (int i = 0; i < gram; i )
{
pid_t pid;
int fd1[2], fd2[2];
if (pipe(fd1) == -1)
{
return 2;
}
if (pipe(fd2) == -1)
{
return 3;
}
pid = fork();
if (pid < 0)
{
return 1;
}
if (pid > 0)
{
for (int j = 0; j < steiles; j )
{
arr2[j] = arr[i][j];
}
dump_vector("arr2 - parent", steiles, arr2);
close(fd1[0]);
write(fd1[1], arr2, sizeof(int) * steiles);
close(fd1[1]);
int sum = 0;
close(fd2[1]);
read(fd2[0], &sum, sizeof(int));
close(fd2[0]);
printf("the sum of the row is: %d\n", sum);
}
else
{
close(fd1[1]);
read(fd1[0], arr2, sizeof(int) * steiles);
close(fd1[0]);
dump_vector("arr2 - child", steiles, arr2);
int sum = 0;
for (int k = 0; k < steiles; k )
{
// printf("%d\t", arr2[k]);
sum = arr2[k];
}
printf("Child %d (%d): sum = %d\n", i, getpid(), sum);
close(fd2[0]);
write(fd2[1], &sum, sizeof(int));
close(fd2[1]);
exit(0);
}
}
return 0;
}
static void dump_vector(const char *tag, size_t size, const int *data)
{
int length = printf("%s (%zu):", tag, size);
for (size_t i = 0; i < size; i )
{
length = printf(" -", data[i]);
if (length > 60)
{
length = 0;
putchar('\n');
}
}
if (length > 0)
putchar('\n');
}
I find that functions like dump_vector() are very helpful; I write them for many data structures. Sometimes I accept a FILE *fp argument too, but the tag is crucial. For arrays, size and data are necessary; for single structures, just the structure, of course.
Example output
Dwse mou tis grammes tou pinaka
4
Dwse mou tis steiles tou pinaka
10
12 12 4 3 8 12 6 4 2 10
10 13 14 13 13 1 7 12 4 8
7 12 19 12 14 18 20 13 8 8
5 14 7 11 19 16 4 12 14 18
arr2 - parent (10): 12 12 4 3 8 12 6 4 2 10
arr2 - child (10): 12 12 4 3 8 12 6 4 2 10
Child 0 (15771): sum = 73
the sum of the row is: 73
arr2 - parent (10): 10 13 14 13 13 1 7 12 4 8
arr2 - child (10): 10 13 14 13 13 1 7 12 4 8
Child 1 (15772): sum = 95
the sum of the row is: 95
arr2 - parent (10): 7 12 19 12 14 18 20 13 8 8
arr2 - child (10): 7 12 19 12 14 18 20 13 8 8
Child 2 (15773): sum = 131
the sum of the row is: 131
arr2 - parent (10): 5 14 7 11 19 16 4 12 14 18
arr2 - child (10): 5 14 7 11 19 16 4 12 14 18
Child 3 (15774): sum = 120
the sum of the row is: 120