如何丢弃以boost::asio发送的数据？
我正在编写一些使用boost::asio类读写串行设备的代码。然而，当在程序之间发送几个字符串时，我注意到在接收程序中，数据是按照写入串口的顺序读取的，而不是从其他程序发送的数据--如果几秒钟后我开始读取数据，我就不会得到当前发送的值，而是以前发送的值。我假设这是我设置boost::asio::serial_port的方式造成的
int main(int argc, char const *argv[]){
int baud=atoi(argv[1]);
std::string pty=argv[2];
printf("Virtual device: %s\n",pty.data());
printf("Baud rate: %d\n",baud);
boost::asio::io_service io;
boost::asio::serial_port port(io, pty);
port.set_option(boost::asio::serial_port_base::baud_rate(baud));
// counter that writes to serial port in 1s intervals
int val=0;
while (1){
std::string data=std::to_string(val);
data+='\n';
std::cout << data;
write(port,boost::asio::buffer(data.c_str(),data.size()));
sleep(1);
val++;
data.clear();
}
port.close();
return 0;
}在将新值发送到串行端口(我认为应该在代码的写()部分上完成)时，是否有一种方法强制丢弃过去的数据？
回答 1
Stack Overflow用户
发布于 2014-03-23 23:04:06
Boost.Asio不提供用于刷新串口缓冲区的更高级别的抽象。但是，这通常可以通过让特定于平台的调用(如tcflush()或PurgeComm() )在串口的手柄()上操作来实现。
每个串行端口都有一个接收和发送缓冲器，并且在一个或两个缓冲器上进行刷新操作。例如，如果连接了两个串行端口(/dev/pts/3和/dev/pts/4)，并且程序A打开并写入了/dev/pts/3，那么它只能刷新与/dev/pts/3相关的缓冲区(在/dev/pts/3上接收的数据没有读取，数据被写入/dev/pts/3但没有传输)。因此，如果程序B启动、打开/dev/pts/4并希望读取非陈旧数据，那么程序B需要在打开串口后为/dev/pts/4刷新接收缓冲区。
这里是一个运行在CentOs上的完整示例。当该示例作为编写器运行时，它将每秒钟向串行端口写入一个顺序递增的数字。当该示例作为编写器运行时，它将读取5个数字，睡眠5秒，并每隔一次迭代刷新其读取缓冲区：
#include <iostream>
#include <vector>
#include <boost/asio.hpp>
#include <boost/thread.hpp>
/// @brief Different ways a serial port may be flushed.
enum flush_type
{
flush_receive = TCIFLUSH,
flush_send = TCOFLUSH,
flush_both = TCIOFLUSH
};
/// @brief Flush a serial port's buffers.
///
/// @param serial_port Port to flush.
/// @param what Determines the buffers to flush.
/// @param error Set to indicate what error occurred, if any.
void flush_serial_port(
boost::asio::serial_port& serial_port,
flush_type what,
boost::system::error_code& error)
{
if (0 == ::tcflush(serial_port.lowest_layer().native_handle(), what))
{
error = boost::system::error_code();
}
else
{
error = boost::system::error_code(errno,
boost::asio::error::get_system_category());
}
}
/// @brief Reads 5 numbers from the serial port, then sleeps for 5 seconds,
/// flushing its read buffer every other iteration.
void read_main(boost::asio::serial_port& serial_port)
{
std::vector<unsigned char> buffer(5);
for (bool flush = false;; flush = !flush)
{
std::size_t bytes_transferred =
read(serial_port, boost::asio::buffer(buffer));
for (std::size_t i = 0; i < bytes_transferred; ++i)
std::cout << static_cast<unsigned int>(buffer[i]) << " ";
boost::this_thread::sleep_for(boost::chrono::seconds(5));
if (flush)
{
boost::system::error_code error;
flush_serial_port(serial_port, flush_receive, error);
std::cout << "flush: " << error.message() << std::endl;
}
else
{
std::cout << "noflush" << std::endl;
}
}
}
/// @brief Write a sequentially increasing number to the serial port
/// every second.
void write_main(boost::asio::serial_port& serial_port)
{
for (unsigned char i = 0; ; ++i)
{
write(serial_port, boost::asio::buffer(&i, sizeof i));
boost::this_thread::sleep_for(boost::chrono::seconds(1));
}
}
int main(int argc, char* argv[])
{
boost::asio::io_service io_service;
boost::asio::serial_port serial_port(io_service, argv[2]);
if (!strcmp(argv[1], "read"))
read_main(serial_port);
else if (!strcmp(argv[1], "write"))
write_main(serial_port);
}用socat创建虚拟串口
$ socat -d -d PTY: PTY:
2014/03/23 16:22:22 socat[12056] N PTY is /dev/pts/3
2014/03/23 16:22:22 socat[12056] N PTY is /dev/pts/4
2014/03/23 16:22:22 socat[12056] N starting data transfer loop with
FDs [3,3] and [5,5]开始读和写示例：
$ ./a.out read /dev/pts/3 & ./a.out write /dev/pts/4
[1] 12238
0 1 2 3 4 noflush
5 6 7 8 9 flush: Success
14 15 16 17 18 noflush
19 20 21 22 23 flush: Success
28 29 30 31 32 noflush
33 34 35 36 37 flush: Success正如输出中所演示的那样，只有当读取器刷新其读取缓冲区：3 4 noflush 5 6 7 8 9 flush 14 15时，才会在序列中跳过数字。
https://stackoverflow.com/questions/22581315
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