从外部过程管道阅读时，fgets卡在

发布于 2025-02-03 05:01:12 字数 839 浏览 4 评论 0原文

我正在从popen中调用iperf3，然后从其输出中读取到字符串中。

#include <stdio.h>
#include <iostream>

using namespace std;

int main() {
  string peer_ip = "localhost";

  string iperf_cmd = "iperf3 -c " + peer_ip + " -t 1" + " -R 2>&1";
  string iperf_out;
  char iperf_buff[2];

  FILE *iperf_d = popen(iperf_cmd.c_str(), "r");
  while (fgets(iperf_buff, 2, iperf_d) != nullptr)
    iperf_out += iperf_buff;
  pclose(iperf_d);

  cout << iperf_out << "\n";
}

这大多数时候都起作用。

但是，当网络非常慢时，我的fgets被卡住了，并且程序切勿从iperf3中打印输出。这是为什么？

来自MAN FGETS（3）：

fgets（）读取最多比流的大小字符少。并将它们存储到s指向的缓冲区中。阅读停止在EOF或NEWLINE之后。如果读取新线，则将其存储在缓冲区。最后一个终止null字节（'\ 0'）是在上次之后存储的缓冲区中的字符。

请注意，我的缓冲区长2个字节。

原文

I'm calling iperf3 from via popen and read from its output into a string.

#include <stdio.h>
#include <iostream>

using namespace std;

int main() {
  string peer_ip = "localhost";

  string iperf_cmd = "iperf3 -c " + peer_ip + " -t 1" + " -R 2>&1";
  string iperf_out;
  char iperf_buff[2];

  FILE *iperf_d = popen(iperf_cmd.c_str(), "r");
  while (fgets(iperf_buff, 2, iperf_d) != nullptr)
    iperf_out += iperf_buff;
  pclose(iperf_d);

  cout << iperf_out << "\n";
}

This works most of the time.

However, when the network is is very slow, my fgets gets stuck and program never prints the output from iperf3. Why is that?

From man fgets(3):

fgets() reads in at most one less than size characters from stream
and stores them into the buffer pointed to by s. Reading stops
after an EOF or a newline. If a newline is read, it is stored into
the buffer. A terminating null byte ('\0') is stored after the last
character in the buffer.

Note that my buffer is 2 bytes long.

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