Writing an array of ints to pipe

Question

I am having trouble trying to write and read from a pipe. I have to create an array of prime numbers and write that array to a pipe to be read that array from the pipe. I have tried multiple different ways but cannot figure it out.

Here is my code.

#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <stdlib.h>
#include <string>
#include <iostream>
#include <sstream>
#include <string.h>
using namespace std;

int main(int argc, char *argv[]){

int n = 10000;
int array[n] = {0};
int nums[n] = {0};
int k = 0;
int answer[argc] = {0};

//this loop makes an array or prime numbers acording to the node
//if that node number is not a prime number it puts a 0 in that node
for(int i =2; i < n; i++){
    for(int j = (i*i); j < n; j+=i){
        array[j-1] = 1;
    }
}
//this loop makes an array of all the prime numbers;
for(int i = 1; i < n; i++){
    if(array[i -1] == 0){
        nums[k] = i;
        k++;
    }
}
//this loop puts the selected prime numbers in the array
for(int j = 1; j < argc; j++){
    int num = atoi(argv[j]);
    answer[j - 1] = nums[num];
}
//this loop prints the primes for testing
for(int i = 1; i < argc; i++)
    cout << answer[i - 1] << endl;


int fd[2], nbytes;
pid_t childpid;
string number;
int readbuffer[90]; 
string numbers;
pipe(fd);

if((childpid = fork()) == -1){
    perror("fork");
    exit(1);
}

if(childpid == 0){

    close(fd[0]);
    for(int i = 0; i < argc; i ++){

    write(fd[1], &answer[i], sizeof(int));
    }
    exit(0);
}

else{
    close(fd[1]);
    for(int i = 0; i < argc; i++){
        nbytes = read(fd[0], readbuffer, sizeof(int));
        printf("recieved string: %s", readbuffer);
    }
}

}

Answer 1

You write byte encoding of int values

write(fd[1], &answer[i], sizeof(int))

read them correctly

nbytes = read(fd[0], readbuffer, sizeof(int))

but try to print them as C-strings

printf("recieved string: %s", readbuffer)

Your compiler should have complain about wrong type here. Replace by

printf("...%d\n",*readbuffer);

Beware that you are using C-streams while your code is C++. It will be better to use C++-streams...