Question

Assume each POSIX API call (fork, write, etc.) does not fail. Which of the following are possible outputs?

write(STDOUT_FILENO, "A", 1);
int value = 0;
pid_t pid1 = fork();
if (pid1 == 0) {
    write(STDOUT_FILENO, "B", 1);
    value += 1;
} else {
    write(STDOUT_FILENO, "C", 1);
    value += 2;
}
pid_t_pid2 = fork();
char value_as_string[2];
sprintf(value_as_string, "%d", value);
write(STDOUT_FILENO, value_as_string, 1);

1. ABC1122

2. ACB1122

3. ABC3333

4. AC22B11

5. AC22C33

6. AC221B1

Please explain how you got the possible outputs. Thanks!

Answer 1

Option 4.AC22B11 is the right answer.

Explanation:

It will print A as per write command. pid1 is the childprocess created. But when the program is executed first the if condition fails and it will print the C value in the else part and since value is 2 there number 2 gets printed.The sprintf statement holds the value 2 hence again 2 is printed(AC22). Then second time it goes inside the child process and prints the B character and the value is 1 there so 1 is printed.