为什么在使用fprintf时stdout没有打印?

I have this code:

我有这段代码:

#include <stdio.h>
#include <unistd.h>
int main()
{
        while(1)
        {
                fprintf(stdout,"hello-out");
                fprintf(stderr,"hello-err");
                sleep(1);
        }
        return 0;
}

The output is hello-err hello-err hello-err hello-err hello-err hello-err at 1 sec intervals. I want to know why hello-out never gets printed.

输出是hello-err hello-err hello- ur -err，每间隔1秒。我想知道为什么helloout永远不会被打印出来。

2 个解决方案

#1

You need to fflush stdout because usually stdout is line buffered and you don't issue a new line character in your program.

您需要fflush stdout，因为通常stdout是行缓冲的，而且在程序中不会发出新的行字符。

            fprintf(stdout,"hello-out");
            fflush(stdout);

stderr is not fully buffered by default so you don't need to fflush it.

stderr在默认情况下没有完全缓冲，所以不需要填充它。

#2

stdout is line-buffered by default, meaning that the buffer will be flushed at every end-of-line ('\n'). stderr is unbuffured, so every character is sent automatically without the need to flush.

默认情况下，stdout是行缓冲的，这意味着缓冲区将在每个行结束时刷新('\n')。stderr是无缓冲的，所以每个字符都是自动发送的，不需要刷新。

You can confirm this by placing a \n at the end of the stdout output. That way both lines will be printed at 1 second intervals.

您可以在stdout输出的末尾放置一个\n来确认这一点。这样，两行每隔1秒打印一次。

#1