使用叉与C [英] Using fork with c

问题描述

这是一个学术问题如此的原因是理解输出。

It is an academic question so the reason is to understand the output.

我有一个code：

int main(int argc, char **argv) {
            int k ;
            while(*(++argv)) {
                    k = fork();
                    printf("%s ",*argv);
            }
    return 0;
    }

结果
与运行程序：PROG A B结果
输出是：

running the program with : prog a b
The output is :

  a b a b a b a b

为什么我得到这样的结果？

Why do I get this result?

推荐答案

由于在意见提出由克里斯·卢茨，你正在观察所使用的静态缓冲区的作用的printf 在叉（）呼叫被复制。由第一叉创建的两个过程（）不打印 B 如果（因为你能想到的，如发生强制刷新）。他们都打印 A B 因为它们都具有一个挂起，未刷新 A 在各自的缓冲器。

As suggested by Chris Lutz in the comments, you are observing the effect of a static buffer used by printf being duplicated by the fork() call. The two processes created by the first fork() do not print b (as you could expect, and as happens if you force a flush). They both print a b because they both have a pending, unflushed a in their respective buffers.

有4个过程（2 ^ 2，包括最初的一个），它们都只有真正打印在出口时，缓冲区被刷新，并且它们都具有 AB 中当时他们各自的缓冲器。

There are 4 processes (2^2, including the initial one), they all only really print at exit when the buffer is flushed, and they all have a b in their respective buffers at that time.

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