将换行符添加到 printf() 是否等同于刷新流? [英] Is adding the newline character to printf() equivalent to flushing the stream?

问题描述

以下程序显示了在发生除以零"等错误时，缓冲 I/O 如何导致程序出现问题:

The following program shows how buffered I/O can cause problems in programs when errors like 'divide by zero' happen:

int main()
{
    int a = 1, b = 0, c;

    printf("Dividing...");
    c = a/b;

    printf("Answer is: %d\n", c);
    return 0;
}

输出为浮点异常(核心转储).

很公平.但令人惊讶的是，如果我将第一个 printf 更改为 printf("Dividing...\n");，则该文本实际上会在程序崩溃之前打印出来(我在 Linux 上运行 GCC，通过方式).

Fair enough. But surprisingly, if I changed the first printf to printf("Dividing...\n");, this text actually gets printed before the program crashes (I'm running GCC on Linux, by the way).

我是否可以得出添加换行符等同于刷新的结论?如果是这样，如果我所有的 printf() 字符串都以 \n 结尾，我实际上是在剥夺自己享受缓冲 I/O 的好处吗?

Am I to conclude that adding a newline is equivalent to flushing? And if so, if all my printf() strings end in \n, I'm actually depriving myself of the benefits of buffered I/O?

推荐答案

如果你的标准输出是去终端，是的，它等于刷新，因为 printf() 将使用基于行的缓冲.

If your standard output is going to a terminal, yes, it's equal to flushing, as printf() will use line-based buffering.

如果它被重定向到一个文件，那么没有.在这种情况下，printf() 使用更大的缓冲区(通常对应于文件系统块大小或其他大小)来优化 IO.

If it's redirected to a file, then no. In this case printf() uses much bigger buffers, usually corresponding to file system block sizes or whatever, to optimize IO.

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