fork() doesn't do what I want - c

Question

So,my programm should do this: I write in the parent process a message to the file "vaterkind" and then read it with the child process, write it to a string and put it on the screen. I tried with this code:
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <sys/stat.h>
int main()
{
FILE *vaterkind, *kindvater;
char path1[]={"/home/user/Documents/vaterkind"}, path2[]={"/home/user/Documents/kindvater"}; //paths to files
int ret, readyv=0, readyk=0;
mkfifo(path1,0666); //makes fifos
mkfifo(path2,0666);
ret = fork();
if(ret > 0) //parent
{
char data_in[50];
char data_out[50];
puts("String");
gets(data_in);
vaterkind = open(path1,O_WRONLY); //dad is able to write
kindvater = open(path2,O_RDONLY); //child is able to read
write(vaterkind,data_in,strlen(data_in)); //write input in vaterkind
puts("String sent");
readyv = 1; // set ready
}
else if(ret == 0) // child
{
char data[50],hex[50],ascii[50];
int i = 0, j = 0;
vaterkind = open(path1,O_RDONLY); //dad is able to read
kindvater = open(path2,O_WRONLY); //child is able to write
read(vaterkind,data,strlen(data)); //read input and write to data
puts(data);
puts("Child finished");
return 0;
}
else
{
puts("Fork failed");
}
sleep(1);
return 0;
}
But when I start the program I first get the message "String" then a symbol (don't know why a symbol is here) then "Child finished" then I can do the gets from the parent and then "String sent" it looks like this:
String
Child finished
input
String sent
Can somebody help out please?

Answer 1

In the child branch
char data[50];
...
read(vaterkind,data,strlen(data))
At that point data contains garbage and applying strlen to it makes no sense at all.
(That's not even mentioning that the parent sends a string without a zero-terminator and the child never bothers to zero-terminate what it received.)
You are supposed to develop a communication protocol of some sort to make sure that at any point the child knows how many bytes it should read from FIFO. For example, the parent can first send the length of the string and only then the contents of the string. The child begins by reading the length and proceeds from there.

Answer 2

Your read in child process is not blocked.
so it wont wait till parent process is finished.
you have to use a pipe from parent to child.
Write into pipe from parent end.
read from the pipe in child.
This blocks the child process, till reading is complete.
Below is simple design for your understanding and how to do it.
int main(int argc, char *argv[])
{
//Two file descriptors for pipe read and write.
int fd[2];
// create a pipe with defined file descriptors
pipe(fd);
// fork() returns 0 for child process.
//so below is a parent process.
if (fork() != 0)
{
// close read-descriptor, you are only writing in parent.
close(fd[0]);
//write into the pipe
write(fd[1], "your data to write", sizeof("your data"));
// close the write descriptor
close(fd[1]);
}
else
{
// close the write-descriptor, you are only reading here
close(fd[1]);
// read here. this will block the process till your reading complete.
read(fd[0], "your variable to read", sizeof("your variable"));
// close the read-descriptor
close(fd[0]);
}
return 0;
}