正确使用fork，wait，exit等-Correctusageoffork,wait,exit,etc

Use waitpid() to garner the exit statuses of the child processes in sequence; using wait() makes no guarantee about the sequence in which the child corpses will be retrieved.

使用waitpid()按顺序获取子进程的退出状态;使用wait()不能保证检索子尸体的顺序。

On Unix, the exit status is limited to 8 bits, which can be treated as signed or unsigned by the program retrieving the data. You also get an 8 bit value identifying the signal number and core dump status of the terminated child. AFAIK, either the status or the signal bits are always zero (and often both - when the process exits successfully).

在Unix上,退出状态限制为8位,可以通过检索数据的程序将其视为有符号或无符号。您还可以获得一个8位值,用于标识已终止子项的信号编号和核心转储状态。 AFAIK,状态或信号位始终为零(通常两者都是 - 当进程成功退出时)。

If you don't know that the numbers to be returned are smaller than 256, then exit status is not the way to go. As others have said, you have to use some other IPC in that case. If the only system calls permitted are those, then you have to conclude that the values will be less than 255, or that overflows don't matter. Neither is satisfactory as a conclusion outside a homework exercise, but in the 'real world', you are not limited to just 4 system calls either.

如果您不知道要返回的数字小于256,则退出状态不是可行的方法。正如其他人所说,在这种情况下你必须使用其他一些IPC。如果允许的唯一系统调用是那些,那么你必须得出结论,这些值将小于255,或者溢出无关紧要。作为家庭作业之外的结论,两者都不令人满意,但在“现实世界”中,您不仅限于4个系统调用。

See also Exit codes bigger than 255?. Note that on Windows, the range of exit codes is much larger - but you don't use the system calls listed in the question.

另请参阅大于255的退出代码?请注意,在Windows上,退出代码的范围要大得多 - 但您不使用问题中列出的系统调用。

Observation: when I do exit(1), the value in status from wait() is 256; is there a reason for that?

观察:当我退出(1)时,来自wait()的状态值为256;这是有原因的吗?

Answer: yes. The low 8 bits of the status word encode the signal number and so on; the high 8 bits of the (16-bit) status word encode the exit status.

答:是的。状态字的低8位编码信号编号,依此类推; (16位)状态字的高8位编码退出状态。

See and macros WIFEXITED(), WEXITSTATUS(), etc.

请参阅 和宏WIFEXITED(),WEXITSTATUS()等。

I think what you are doing should work fine - just return the number of occurrences as the exit code from the process.

我认为你正在做的事应该可以正常工作 - 只需将出现次数作为退出代码从流程中返回。

You mention that exit() will only allow numbers below 256. I highly doubt if this is the case, but it would be simple enough for you to write a test program to find out for sure.

你提到exit()只允许低于256的数字。我非常怀疑是否是这种情况,但你可以很简单地编写一个测试程序来确定。

Sounds like this is really just a simplified version of Map-Reduce. You might want to have a look at that algorithm as well for some ideas on how you could further parallelize the program - and maybe get some extra credit :)

听起来像这只是Map-Reduce的简化版本。你可能想看看那个算法以及关于如何进一步并行化程序的一些想法 - 并且可能得到一些额外的功劳:)

As for the difference between wait() and waitpid() - if you just want to wait for any of your child processes to complete, you would use wait(). If you want to wait only for a specific child process or if you wanted to just check if a child process has exited without hanging, you would use waitpid().

至于wait()和waitpid()之间的区别 - 如果你只想等待任何子进程完成,你可以使用wait()。如果您只想等待特定的子进程,或者只是想检查子进程是否已经退出而没有挂起,那么您将使用waitpid()。