Problem with multidirectional pipe (father <-> son) - c

Question

My little program includes two pipes to create a multidirectional communication between father and son.
The write on s2f [1] returns -1 but I did not understand why.
Can you help me? Is there anything else that does not work or that I could improve?
/*
Write a program in C language that in sequence:
1) create 2 pipes and a child (the 2 pipes will be used for two-way communication between the parent
and son);
2) the father, after the creation of the child, takes in input from the user a file name;
3) send the child the name of the file using the first pipe;
4) make the child look for the number of spaces in the file and communicate this number to the father through the use of the second pipe;
5) let the father print the number received from son;
*/
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/wait.h>
int main (int argc, char *argv[])
{
int f2s[2];
int s2f[2];
int fd, n;
pid_t p;
char buf[20];
char c;
int countspace=0, valueofspace;
if (argc<2)
{
printf("ERROR!\n");
exit (-1);
}
if (pipe (f2s) == -1 && pipe (s2f) == -1)
exit(-1);
p=fork();
if (p>0)
{
printf("I'm inside the father process.\n");
close(f2s[0]);
close(s2f[1]);
write(f2s[1],argv[1],sizeof(argv[1]));
read(s2f[0],&valueofspace, sizeof(int));
printf("The spaces are %d", valueofspace);
printf("Father exit\n");
exit(0);
}
if (p==0)
{
printf("I'm inside the child process.\n");
close(f2s[1]);
close(s2f[0]);
read (f2s[0],buf,20);
if (fd = open(buf, O_RDONLY) == -1)
printf("Error when opening the file\n");
while (read(fd,&c,1) > 0)
{
if (c==' ')
countspace++;
}
close(fd);
printf("Count: %d\n",countspace);
n = write(s2f[1],&countspace, sizeof(countspace));
printf("WRITE of %d BYTES\n", n);
printf("Son exit \n");
exit(0);
}
}

Answer 1

You have closed the reading end of the pipe s2f before writing into it.
close(s2f[0]);
So there will be a EPIPE error when you write into the pipe. From the online reference on write (with added emphasis):
The EPIPE error occurs when fd is connected to a pipe or socket whose reading end is closed. When this happens the writing process will also receive a SIGPIPE signal. (Thus, the write return value is seen only if the program catches, blocks or ignores this signal.)
Since your program does not catch, block or ignore this signal, the write return value is not as expected and instead is -1.