why I'm not getting the stdout result from the child process - c

Question

I have two programs: Program "Vanilla", and program "verB".
My instructions are that the main process will deal with I\O from the user, and the child will call execve() and run the "Vanilla" process. To accomplish this, I have to use dup2() to replace stdin\stdout on both pipes. (The Vanilla program should use fgets() to read from the pipe).
Inside the "Vanilla" program I read two strings from the user until ctrl+D is pressed, Vanilla calls "xorMethod()" which is doing something (not relevant what) and returns a result.
When I run the "verB" program on Linux(), I only get the "Please insert first, the second string" and then nothing happens and the program stops running.
I want that the parent will continue getting two strings until ctrl+D is pressed, and print the result that he got from his child on the screen.
Vanilla.c
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include "Vanila.h"
#include "xor.h"
#define MAXLEN 80
int main()
{
char s1[MAXLEN + 1];
char s2[MAXLEN + 1];
while (!feof(stdin))
{
if (readString(s1) == -1)
break;
if (readString(s2) == -1)
break;
fflush(stdin);
int res = xorMethod(s1, s2);
printf("%s xor %s = %d", s1, s2, res);
}
return 1;
}
int readString(char * string)
{
if ((fgets(string, MAXLEN + 1, stdin) < 0 || feof(stdin)))
return -1;
string[strcspn(string, "\n")] = 0;
return 1;
}
verB.c
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include "Vanila.h"
#define MAXLEN 80
int readStr(char * string);
int main()
{
int pipeToChild[2];
int pipeToParent[2];
char * argv[] = { "./Vanilla",NULL };
if (pipe(pipeToChild) == -1)
return -1;
if (pipe(pipeToParent) == -1)
return -1;
pid_t pid = fork();
if (pid == -1)
return -1;
if (pid == 0) //CHILD proccess
{
close(pipeToChild[0]);
close(pipeToParent[1]);
dup2(pipeToChild[0], fileno(stdin));
dup2(pipeToParent[1], fileno(stdout));
execve(argv[0], argv, NULL);
}
else
{
char string1[MAXLEN + 1];
char string2[MAXLEN + 1];
char result[MAXLEN + 1];
close(pipeToChild[0]);
close(pipeToParent[1]);
while (!feof(stdin))
{
printf("Please insert first string : ");
if (readStr(string1) == -1)
return -1;
printf("Please insert second string : ");
if (readStr(string2) == -1)
return -1;
write(pipeToChild[1], string1, strlen(string1));
write(pipeToChild[1], string2, strlen(string2));
read(pipeToParent[0], &result, MAXLEN);
printf("%s\n", result);
}
wait(NULL);
}
return 1;
}
int readStr(char * string)
{
if ((fgets(string, MAXLEN + 1, stdin) < 0 || feof(stdin)))
return -1;
string[strcspn(string, "\n")] = 0;
return 1;
}

Answer 1

You close the wrong ends of the pipes in the child process. You close the read end of pipeToChild and then dup2 the standard input stream, so you child program will have a closed standard input stream. You should close the write end of pipeToChild and the read end of pipeToParent in the child process, and the other way around in the main process:
if (pid == 0) //CHILD proccess
{
close(pipeToChild[1]);
close(pipeToParent[0]);
/* ... */
else //PARENT
{
close(pipeToChild[0]);
close(pipeToParent[1]);