我得到一个编译错误，另外我不能在不给它数组元素的情况下提升:: asio :: read buf。
std::string eport::read_data (void)
{
io_service io; // create the I/O service that talks to the serial device
serial_port port (io, PORT); // create the serial device, note it takes the io service and the port name
error_code ec; // address used for error checking
std::string buf [100]; // data with crc on end
try
{
read (port, buffer (buf), ec);
std::cout << "eport::read: result: " << buf << std::endl;
}
catch (error_code &ec)
{
std::cout << "eport::read: ERROR: " << ec << std::endl;
return "error";
}
std::cout << "eport::read: SUCCESS" << std::endl;
return buf;
错误：
eport.cc:83:9: error: could not convert ‘(std::string*)(& buf)’ from ‘std::string* {aka std::basic_string<char>*}’ to ‘std::string {aka std::basic_string<char>}’
该函数是否需要转换为const char *？我不确定是什么问题。感谢任何帮助，谢谢。
更新代码
这是我的代码。我希望它可以帮助某人，因为asio缺乏网上的好例子。我知道我的写功能可以写得更好，而且这段代码还没有经过测试，所以我不确定我是否做得对。感谢。
#include "../include/main.H"
#include <boost/asio.hpp> // asynchronous input/output
#include <boost/crc.hpp> // cyclic redundancy code (for data checking)
using namespace::boost::system;
using namespace::boost::asio;
const char *PORT = "/dev/ttyS0";
// serial port communication setup
serial_port_base::baud_rate BAUD (9600); // what baud rate do we communicate at (default is 9600)
serial_port_base::character_size C_SIZE (8); // how big is each "packet" of data (default is 8 bits)
serial_port_base::flow_control FLOW (serial_port_base::flow_control::none); // what flow control is used (default is none)
serial_port_base::parity PARITY (serial_port_base::parity::none); // what parity is used (default is none)
serial_port_base::stop_bits STOP (serial_port_base::stop_bits::one); // how many stop bits are used (default is one)
int eport::initialize (void)
{
io_service io; // create the I/O service that talks to the serial device
serial_port port (io, PORT); // create the serial device, note it takes the io service and the port name
// set serial port options
port.set_option (BAUD);
port.set_option (C_SIZE);
port.set_option (FLOW);
port.set_option (PARITY);
port.set_option (STOP);
return 0;
}
int eport::write_data (std::string data)
{
io_service io; // create the I/O service that talks to the serial device
serial_port port (io, PORT); // create the serial device, note it takes the io service and the port name
error_code ec; // address used for error checking
boost::crc_32_type crcresult; // used for communication checking
char buf [1024]; // buffer to hold data
int crc; // holds crc value
std::ostringstream convert; // used to convert int to string
std::string data_crc; // data with crc on end
std::stringstream ss; // used to add strings
strncpy (buf, data.c_str(), sizeof(buf)); // put data into buffer
buf [sizeof(buf) - 1] = 0; // make sure the last element has a null
crcresult.process_bytes (buf, sizeof(buf)); // get crc value from buffer contents
crc = crcresult.checksum(); // put crc value into integer
convert << crc; // convert integer to string
ss << data << convert.str (); // add crc string to data string
data_crc = ss.str (); // data string with crc appended to be used in reading / writing
std::cout << "eport::write: data with crc: " << data_crc << std::endl;
std::cout << "eport::write: writing: " << data_crc << std::endl;
write (port, buffer (data_crc, sizeof(data_crc)), ec); // write data with crc to serial device
if (ec) // if error code is true, print and return
{
std::cout << "eport::write: ERROR: " << ec << std::endl;
return -1;
}
std::cout << "eport::write: SUCCESS" << std::endl;
return crc;
}
std::string eport::read_data (void)
{
io_service io; // create the I/O service that talks to the serial device
serial_port port (io, PORT); // create the serial device, note it takes the io service and the port name
error_code ec; // address used for error checking
streambuf sb; // asio stream buffer to hold read data
std::string buf; // read buffer will be put into this string
size_t transferred = read (port, sb, ec); // read data from serial device
buf.resize (transferred); // resize the string to the read data size
sb.sgetn (&buf[0], buf.size ()); // stores characters from the stream to the array
std::cout << "eport::read: result: " << buf << std::endl;
if (ec)
{
std::cout << "eport::read: ERROR: " << ec << std::endl;
return "error";
}
std::cout << "eport::read: SUCCESS" << std::endl;
return buf;
}
答案 0 :(得分：1)
buf是std::string的数组。您应该更改原型或只返回一个字符串。例如buf[0]。
你最想要的可能是：
std::string buf; // No [100]
答案 1 :(得分：1)
您的代码存在问题需要回答，更具体地说，您如何知道将发送到read函数的字符数？
但是，您的问题的一般答案是使用字符数组，然后将其作为std :: string返回：
std::string eport::read_data (void)
{
io_service io; // create the I/O service that talks to the serial device
serial_port port (io, PORT); // create the serial device, note it takes the io service and the port name
error_code ec; // address used for error checking
char buf [100]; // data with crc on end
try
{
read (port, buf, ec);
std::cout << "eport::read: result: " << buf << std::endl;
}
catch (error_code &ec)
{
std::cout << "eport::read: ERROR: " << ec << std::endl;
return "error";
}
std::cout << "eport::read: SUCCESS" << std::endl;
return buf;
}
std::string构造函数将最后将buf复制到std :: string。
现在，如果有办法确定读取的字符数，则必须以不同方式编写函数。大多数read函数都有一个参数，指定要读取的最大字符数，并在某处返回读取的字符数。
假设您可以重写（或调用）具有这两个属性的不同读取函数，代码将如下所示：
std::string eport::read_data (void)
{
io_service io; // create the I/O service that talks to the serial device
serial_port port (io, PORT); // create the serial device, note it takes the io service and the port name
error_code ec; // address used for error checking
char buf [100]; // data with crc on end
int numCharsRead = 0;
try
{
numCharsRead = read2 (port, buf, 100, ec);
std::cout << "eport::read: result: " << buf << std::endl;
}
catch (error_code &ec)
{
std::cout << "eport::read: ERROR: " << ec << std::endl;
return "error";
}
std::cout << "eport::read: SUCCESS" << std::endl;
return std::string(buf, numCharsRead);
}
请注意return的差异。 std :: string是从字符数组构造的，但最多只能有numCharsRead个字符。
答案 2 :(得分：1)
最通用的方法是使用asio::streambuf
streambuf sb;
size_t transferred = read (port, sb, ec);
根据文件：
此函数用于从流中读取一定数量的字节数据。该调用将阻塞，直到满足下列条件之一：
- 提供的缓冲区已满（即已达到最大大小）。
- 发生错误。
此操作是根据对流
read_some函数的零次或多次调用实现的。
然后，将其复制到字符串：
std::string buf;
buf.resize(transferred);
sb.sgetn(&buf[0], buf.size());
或者，预分配预期大小的缓冲区：
std::string buf(100u, '\0');
size_t transferred = read (port, buffer(buf), ec);
buf.resize(transferred);
对于更复杂的方案，请使用read_until：
streambuf sb;
size_t transferred = read_until(port, sb, "\r\n", ec);
这将在"\r\n"遇到read_some之前阅读（注意：可能会阅读更多内容，但在看到分隔符后又不会再次调用ec。）
更复杂的停止条件可以使用overload that takes a MatchCondition functor。
如果您通过error_code接收{{1}}，则不会抛出任何例外