fork()和"\ n" [英] fork() and "\n"

问题描述

我只是在C中制作了一个简单的演示程序，以了解fork()的工作原理，并遇到了我不了解的内容.在此示例中:

I just made a simple demo program in C to see how fork() works and came across something that I don't understand. In this example:

void fork2()
{
    printf("A");
    fork();
    printf("B");
}

输出为ABAB，但在此示例中:

The output is ABAB, but in this example:

void fork2()
{
    printf("A\n");
    fork();
    printf("B\n");
}

输出为ABB(当然是单独的行).第二个是有道理的，因为如果我正确理解fork()，它将产生一个新的子代，该子代在fork()发生的地方之后开始(在本例中为printf("B\n");).我不明白的是，为什么当我包含换行符时输出会有所不同.

The output is ABB (separate lines of course). The second one makes sense, because if I understand fork() correctly it spawns a new child that starts right after where the fork() took place (so printf("B\n"); in this case). What I don't understand, is why the output is different when I include the new line character.

推荐答案

printf()缓冲输出，直到遇到换行符为止.因此，您的\n -less版本会将A塞入输出缓冲区，分叉.

printf() buffers output until a newline is encountered. So your \n-less version stuffs A into the output buffer, forks.

由于两个进程都是相同的(减PID和诸如此类)，所以它们现在都具有包含A的输出缓冲区.

Since both processes are identical (minus PIDs and whatnot), they now both have an output buffer that contains A.

执行继续，并在每个进程的缓冲区中打印B.然后，这两个进程都退出，导致刷新输出缓冲区，该缓冲区两次输出AB，每个进程一次.

The execution continues and prints B into the buffers in each process. Both processes then exit, causing a flush of the output buffer, which prints AB twice, once for each process.

另一个版本为\n的版本会导致在第一次调用printf()之后刷新输出缓冲区，并且当fork命中时，两个进程都有一个空缓冲区.

You other version, having \n, causes that output buffer to flush after the first printf() call, and when the fork hits, both processes have an empty buffer.

这篇关于fork()和"\ n"的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！