程序流，带有逻辑的fork（）

Question

我试图理解这个简单的C fork（）代码的流程：

fork() && fork() || fork();
fork();
printf("forked ");

对我来说（g ++）的输出是：

forked forked forked forked forked forked forked forked forked 

单步执行并不能真正帮助我理解它。

Answer 1

fork() && fork() || fork();
^^^^^^^^^^^^^^^^
Parent forks a child with return value 0 for the child process. 
Since it is logical AND operator, the short-circuit evaluation applies, 
so the child doesn’t go further. Parent goes on forking again(right-hand-side of AND). 
There are 3 processes being composed of 2 children and 1 parent.



fork() && fork() || fork();
                    ^^^^^^
                    Again parent forks one more and since OR operator
                    doesn’t apply short-circuit for latter child
                    (due to return type which is 0 and left-hand-side of OR op.), 
                    the latter child forks as well. There are totally 5 processes.

 fork()[fourth]; doubles prior number of processes 5*2 = 10 processes totally exist.

您的输出很有可能被缓冲。尝试fprintf(stderr, "forked ");，fflush(stdout)或printf("forked\n”);。

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我认为以下附图会有所帮助。