Pipe, Fork, and Exec - Two Way Communication Between Parent and Child Process

Question

An assignment in my Operating Systems class requires me to build a binary process tree by recursively calling exec on the same program. The goal is to split some arbitrary task

Answer 1

Besides the issue mentioned by Jonathon Reinhart, most probably the call to execv() fails.

To test this modify these lines

execvp("two_way_pipes", argv2);
_exit(0);

to be

...
#include 
...


execvp("two_way_pipes", argv2); /* On sucess exec*() functions never return. */
perror("execvp() failed); /* Getting here means execvp() failed. */
_exit(errno);

Expect to receive

execvp() failed: No such file or directory

To fix this change

execvp("two_way_pipes", argv2);

to be

execvp("./two_way_pipes", argv2);

---

Also if the child was not exec*()ed then this line

read(PARENT_READ, buff, 4); // should read "test" which was written by the child to stdout

fails and in turn buff is not initialised and therefore this line

fprintf(stderr, "in parent | message received: %s\n", buff);  

provokes undefined behaviour.

To fix this at least properly initialise buff by changing

char buff[5];

to be

char buff[5] = "";