One of the child processes can't read from pipe - c

Question

I am trying to implement a small IPC in C, but I have an issue that I can't solve.
My main process have two children, child A and child B; Child A gets created first.
I have two pipes to pass information to these processes, pipefd and pipefd2.
First, parent process reads a file's content, and writes to both pipes these two values:
1-length of the string
2-string itself
Once they get the length of string, they create a char array with the given length, and then read the string into this array.
Then both children read from their pipes. Child B can get these values correctly from the pipe, but child A gets 0 as size.
Here's my code, thanks for your time!
Output :
Child A here, input read, size is: 0
Size is 45169child reads input, size : 45169
Child B here, input read, size is: 45169
//
// Created by Dilara on 16.02.2020.
//
#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
#include <time.h>
#include <signal.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <string.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <sys/wait.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#define MESSAGESIZE 10
#define READ_END 0
#define WRITE_END 1
int fsize(FILE *fp){
int prev=ftell(fp);
fseek(fp, 0L, SEEK_END);
int sz=ftell(fp);
fseek(fp,prev,SEEK_SET); //go back to where we were
return sz;
}
void writeToPipe(int fd[2], char string[], long stell){
close(fd[READ_END]);
write(fd[WRITE_END], stell, sizeof(stell));
write(fd[WRITE_END], string, strlen(string)+1);
close(fd[WRITE_END]);
}
static void readFromPipe(int pipefd[2], char input[],long size){
// wait(NULL);
close(pipefd[WRITE_END]);
read(pipefd[READ_END], input, size);
printf("child reads input, size : %d \n",size);
close(pipefd[READ_END]);
}
static long readSize(int pipefd[2]){
long size;
close(pipefd[WRITE_END]);
read(pipefd[READ_END], size, sizeof(size));
printf("Size is %d",size);
close(pipefd[READ_END]);
return size;
}
int main()
{
int pipefd[2];
int pipefd2[2];
  int childA_pid;
int childB_pid;
if (pipe(pipefd) == -1)
{
perror(" pipe");
return 0;
}
if (pipe(pipefd2) == -1)
{
perror(" pipe");
return 0;
}
childA_pid = fork();
    if(childA_pid == 0){
//childA
long SIZE = readSize(pipefd);
char input[SIZE];
readFromPipe(pipefd, input, SIZE);
printf("Child A here, input read, size is: %d \n",SIZE);
}
else{
childB_pid = fork();
if(childB_pid == 0){
long SIZE = readSize(pipefd2);
char input[SIZE];
readFromPipe(pipefd2, input, SIZE);
printf("Child B here, input read, size is: %d \n",SIZE);
}else{
//parent
char *buffer;
FILE *fp = fopen("try.txt", "r");
if (fp != NULL)
{
fseek(fp, 0L, SEEK_END);
long stell = ftell(fp);
rewind(fp);
char str[stell];
buffer = (char *)malloc(stell);
if (buffer != NULL)
{
//fread(buffer, stell, 1, fp);
fread(str,stell,1, fp);
// printf("%s", str);
fclose(fp);
fp = NULL;
free(buffer);
}
printf("SIZE: %d", stell);
writeToPipe(pipefd2, str,stell);
writeToPipe(pipefd, str,stell);
}
}
   
}
 return 0;
}

Answer 1

write(fd[WRITE_END], stell, sizeof(stell));
I think your code lacks an ampersand here. Instead of the stell variable you should use its address:
write(fd[WRITE_END], &stell, sizeof(stell));