Consider this:
main()
{
int i = 1;
fork(); fork(); fork();
printf("%d ",i);
}
The output of the above code is:
1 1 1 1 1 1 1 1
That is, at the end there are 8 (2^3) processes reaching the printf() line. Now consider the code below:
main()
{
int i = 1;
fork() && fork() || fork();
printf("%d ",i);
}
Initially, I thought there'd be no change in the output because the results of the comparisons using && , || are not being evaluated by a control statement like if or while. That is, they're being discarded. However, The output of this code is:
1 1 1 1 1
Meaning, at the end there are 5 processes that reach the printf() line.
My question: What does this line do
fork() && fork()||fork();
Definitely, something has changed. I've never contemplated using comparison operators like && , || without control statements like if, while to evaluate the result of the comparison and accordingly take some action. I thought, without these control constructs, the comparison operators are meaningless; they'd simply return 1 or 0 without anything being done about it.
Clearly, I'm mistaken, and am totally unaware of this usage of the operators.
fork() returns the PID for a child process if it’s returning in the parent, or 0 if it’s returning in the child. Logical operators short-circuit in C, so a && b doesn’t evaluate b if a is 0, and a || b doesn’t evaluate b if a is not 0.
So you fork once. Two processes. The right side of the && only gets evaluated in the child. Three processes. The right side of the || gets evaluated in the same child again. Four processes. But wait! && binds tighter than ||, so the parent process also forks again, for a total of five processes.
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