Recursive Fibonacci using a fork (in C)

Question

I am trying to write a function that recursively computes the resulting fibonacci number from a given int n using forks in C.

Here is the specification of the function: If the print is correct, print it. Otherwise, provide the parent process. The solution must be recursive, and it must develop a new child for each challenge. Each process must call doFib () exactly once. The signature of the method cannot be changed. You cannot use helper functions.

Here is what I have written so far based on my understanding of the plug. I am trying to split twice, so I can create two child processes. One to make fib (n-1) and one to make fib (n-2). That way I can capture both results and combine them.

static void doFib(int n, int doPrint) { pid_t pid1; pid_t retpid1; int status1; pid_t pid2; pid_t retpid2; int status2; pid = fork(); if (pid == 0) // Child Process 1 { exit(100); // sends 100 to the parent } else if (pid > 0) // Parent Process 1 { pid2 = fork(); if (pid2 == 0) // Child Process 2 { exit(200); // sends 200 to the parent } else if (pid2 > 0) // Parent Process 1 { } retpid = waitpid(pid,&status,0); if (pid != retpid) { printf("waitpid error\n"); } printf("I got this value from my child process 1: %d\n", WEXITSTATUS(status)); } } 

My questions:

1. How to get both values ​​from two child processes? I know how to capture one (see Code), but how can I capture them?

2. Since doFib does not return a value, how do I get the value of my doFib call in any of my child processes so that I can combine them?

3. Am I doing my job right? I was sure of one plug, two had a headache.

This is an interim issue in the practice of the series that I am currently working on to prepare for the upcoming exam.

Answer 1

1) Call waitpid twice.

2) Calling waitpid will put it in status .

3) Two things: first, to end the forked process, use _exit , not exit . The exit function may corrupt file descriptors that the parent is still using. In your case, it does not matter, but why learn bad habits? Secondly, you do not need the else if (pid2 > 0) . That is all that remains.