使用fork与c(Using fork with c)

使用fork与c(Using fork with c)

这是一个学术问题，所以理由是要理解输出。

我有一个代码：

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

运行程序：prog ab 输出是：

a b a b a b a b

为什么我得到这个结果？

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

I have a code:

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

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

a b a b a b a b

Why do I get this result?

最满意答案

正如Chris Lutz在评论中所建议的那样，您正在观察由fork()调用复制的printf使用的静态缓冲区的效果。 由第一个fork()创建的两个进程不打印b （正如您所料，并且如果强制刷新则会发生）。 它们都打印ab因为它们在各自的缓冲区中都有待处理的未刷新的a 。

有4个进程（2 ^ 2，包括初始进程），它们只在刷新缓冲区时才真正在出口处打印，并且它们在那时都在各自的缓冲区中都有ab 。

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.

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.