写一个简短的例子：简单的回声程序。请帮忙编译，因为我不明白为什么编译器会出错
我尝试了以下操作：g++ -Wall -Wextra -pedantic client.cpp -o client -lboost_thread -lboost_system，但遇到下一个错误https://pastebin.com/byevYxPa
#include <boost/asio.hpp>
#include <boost/bind.hpp>
#include <string>
using namespace boost::asio;
using error_code = boost::system::error_code;
io_service ioservice;
posix::stream_descriptor out(ioservice, STDOUT_FILENO);
posix::stream_descriptor in(ioservice, STDIN_FILENO);
std::string line;
void on_read(const error_code & err, std::size_t bytes);
void on_write(const error_code & err, std::size_t bytes);
void on_read(const error_code & err, std::size_t bytes) {
if (err || line == "exit") return;
line += "\n";
async_write(out, buffer(line), on_write);
}
void on_write(const error_code & err, std::size_t bytes) {
write(out, buffer("$ "));
async_read_until(in, buffer(line),'\n',on_read);
}
int main() {
async_read_until(in, buffer(line),'\n',on_read);
ioservice.run();
}
我希望这段代码能够正确运行并被编译
client.cpp: In function ‘void on_read(const error_code&, std::size_t)’:
client.cpp:17:50: warning: unused parameter ‘bytes’ [-Wunused-parameter]
void on_read(const error_code & err, std::size_t bytes) {
^~~~~
client.cpp: In function ‘void on_write(const error_code&, std::size_t)’:
client.cpp:25:51: error: no matching function for call to ‘async_read_until(boost::asio::posix::stream_descriptor&, boost::asio::const_buffers_1, char, void (&)(const error_code&, std::size_t))’
async_read_until(in, buffer(line),'\n',on_read);
^
In file included from /usr/include/boost/asio/read_until.hpp:921:0,
from /usr/include/boost/asio.hpp:91,
from client.cpp:1:
/usr/include/boost/asio/impl/read_until.hpp:498:1: note: candidate: template<class AsyncReadStream, class Allocator, class ReadHandler> typename boost::asio::async_result<typename boost::asio::handler_type<WriteHandler, void(boost::system::error_code, long unsigned int)>::type>::type boost::asio::async_read_until(AsyncReadStream&, boost::asio::basic_streambuf<Allocator>&, char, ReadHandler&&)
async_read_until(AsyncReadStream& s,
^~~~~~~~~~~~~~~~
/usr/include/boost/asio/impl/read_until.hpp:498:1: note: template argument deduction/substitution failed:
client.cpp:25:51: note: ‘boost::asio::const_buffers_1’ is not derived from ‘boost::asio::basic_streambuf<Allocator>’
async_read_until(in, buffer(line),'\n',on_read);
^
In file included from /usr/include/boost/asio/read_until.hpp:921:0,
from /usr/include/boost/asio.hpp:91,
from client.cpp:1:
/usr/include/boost/asio/impl/read_until.hpp:701:1: note: candidate: template<class AsyncReadStream, class Allocator, class ReadHandler> typename boost::asio::async_result<typename boost::asio::handler_type<WriteHandler, void(boost::system::error_code, long unsigned int)>::type>::type boost::asio::async_read_until(AsyncReadStream&, boost::asio::basic_streambuf<Allocator>&, const string&, ReadHandler&&)
async_read_until(AsyncReadStream& s,
^~~~~~~~~~~~~~~~
/usr/include/boost/asio/impl/read_until.hpp:701:1: note: template argument deduction/substitution failed:
client.cpp:25:51: note: ‘boost::asio::const_buffers_1’ is not derived from ‘boost::asio::basic_streambuf<Allocator>’
async_read_until(in, buffer(line),'\n',on_read);
^
In file included from /usr/include/boost/asio/read_until.hpp:921:0,
from /usr/include/boost/asio.hpp:91,
from client.cpp:1:
/usr/include/boost/asio/impl/read_until.hpp:913:1: note: candidate: template<class AsyncReadStream, class Allocator, class ReadHandler> typename boost::asio::async_result<typename boost::asio::handler_type<WriteHandler, void(boost::system::error_code, long unsigned int)>::type>::type boost::asio::async_read_until(AsyncReadStream&, boost::asio::basic_streambuf<Allocator>&, const regex&, ReadHandler&&)
async_read_until(AsyncReadStream& s,
^~~~~~~~~~~~~~~~
/usr/include/boost/asio/impl/read_until.hpp:913:1: note: template argument deduction/substitution failed:
client.cpp:25:51: note: ‘boost::asio::const_buffers_1’ is not derived from ‘boost::asio::basic_streambuf<Allocator>’
async_read_until(in, buffer(line),'\n',on_read);
^
In file included from /usr/include/boost/asio/read_until.hpp:921:0,
from /usr/include/boost/asio.hpp:91,
from client.cpp:1:
/usr/include/boost/asio/impl/read_until.hpp:1122:1: note: candidate: template<class AsyncReadStream, class Allocator, class MatchCondition, class ReadHandler> typename boost::asio::async_result<typename boost::asio::handler_type<WriteHandler, void(boost::system::error_code, long unsigned int)>::type>::type boost::asio::async_read_until(AsyncReadStream&, boost::asio::basic_streambuf<Allocator>&, MatchCondition, ReadHandler&&, typename std::enable_if<boost::asio::is_match_condition<MatchCondition>::value>::type*)
async_read_until(AsyncReadStream& s,
^~~~~~~~~~~~~~~~
/usr/include/boost/asio/impl/read_until.hpp:1122:1: note: template argument deduction/substitution failed:
client.cpp:25:51: note: ‘boost::asio::const_buffers_1’ is not derived from ‘boost::asio::basic_streambuf<Allocator>’
async_read_until(in, buffer(line),'\n',on_read);
^
client.cpp:23:34: warning: unused parameter ‘err’ [-Wunused-parameter]
void on_write(const error_code & err, std::size_t bytes) {
^~~
client.cpp:23:51: warning: unused parameter ‘bytes’ [-Wunused-parameter]
void on_write(const error_code & err, std::size_t bytes) {
^~~~~
client.cpp: In function ‘int main()’:
client.cpp:29:51: error: no matching function for call to ‘async_read_until(boost::asio::posix::stream_descriptor&, boost::asio::const_buffers_1, char, void (&)(const error_code&, std::size_t))’
async_read_until(in, buffer(line),'\n',on_read);
^
In file included from /usr/include/boost/asio/read_until.hpp:921:0,
from /usr/include/boost/asio.hpp:91,
from client.cpp:1:
/usr/include/boost/asio/impl/read_until.hpp:498:1: note: candidate: template<class AsyncReadStream, class Allocator, class ReadHandler> typename boost::asio::async_result<typename boost::asio::handler_type<WriteHandler, void(boost::system::error_code, long unsigned int)>::type>::type boost::asio::async_read_until(AsyncReadStream&, boost::asio::basic_streambuf<Allocator>&, char, ReadHandler&&)
async_read_until(AsyncReadStream& s,
^~~~~~~~~~~~~~~~
/usr/include/boost/asio/impl/read_until.hpp:498:1: note: template argument deduction/substitution failed:
client.cpp:29:51: note: ‘boost::asio::const_buffers_1’ is not derived from ‘boost::asio::basic_streambuf<Allocator>’
async_read_until(in, buffer(line),'\n',on_read);
^
In file included from /usr/include/boost/asio/read_until.hpp:921:0,
from /usr/include/boost/asio.hpp:91,
from client.cpp:1:
/usr/include/boost/asio/impl/read_until.hpp:701:1: note: candidate: template<class AsyncReadStream, class Allocator, class ReadHandler> typename boost::asio::async_result<typename boost::asio::handler_type<WriteHandler, void(boost::system::error_code, long unsigned int)>::type>::type boost::asio::async_read_until(AsyncReadStream&, boost::asio::basic_streambuf<Allocator>&, const string&, ReadHandler&&)
async_read_until(AsyncReadStream& s,
^~~~~~~~~~~~~~~~
/usr/include/boost/asio/impl/read_until.hpp:701:1: note: template argument deduction/substitution failed:
client.cpp:29:51: note: ‘boost::asio::const_buffers_1’ is not derived from ‘boost::asio::basic_streambuf<Allocator>’
async_read_until(in, buffer(line),'\n',on_read);
^
In file included from /usr/include/boost/asio/read_until.hpp:921:0,
from /usr/include/boost/asio.hpp:91,
from client.cpp:1:
/usr/include/boost/asio/impl/read_until.hpp:913:1: note: candidate: template<class AsyncReadStream, class Allocator, class ReadHandler> typename boost::asio::async_result<typename boost::asio::handler_type<WriteHandler, void(boost::system::error_code, long unsigned int)>::type>::type boost::asio::async_read_until(AsyncReadStream&, boost::asio::basic_streambuf<Allocator>&, const regex&, ReadHandler&&)
async_read_until(AsyncReadStream& s,
^~~~~~~~~~~~~~~~
/usr/include/boost/asio/impl/read_until.hpp:913:1: note: template argument deduction/substitution failed:
client.cpp:29:51: note: ‘boost::asio::const_buffers_1’ is not derived from ‘boost::asio::basic_streambuf<Allocator>’
async_read_until(in, buffer(line),'\n',on_read);
^
In file included from /usr/include/boost/asio/read_until.hpp:921:0,
from /usr/include/boost/asio.hpp:91,
from client.cpp:1:
/usr/include/boost/asio/impl/read_until.hpp:1122:1: note: candidate: template<class AsyncReadStream, class Allocator, class MatchCondition, class ReadHandler> typename boost::asio::async_result<typename boost::asio::handler_type<WriteHandler, void(boost::system::error_code, long unsigned int)>::type>::type boost::asio::async_read_until(AsyncReadStream&, boost::asio::basic_streambuf<Allocator>&, MatchCondition, ReadHandler&&, typename std::enable_if<boost::asio::is_match_condition<MatchCondition>::value>::type*)
async_read_until(AsyncReadStream& s,
^~~~~~~~~~~~~~~~
/usr/include/boost/asio/impl/read_until.hpp:1122:1: note: template argument deduction/substitution failed:
client.cpp:29:51: note: ‘boost::asio::const_buffers_1’ is not derived from ‘boost::asio::basic_streambuf<Allocator>’
async_read_until(in, buffer(line),'\n',on_read);
^
答案 0 :(得分：0)
asio::buffer返回可变的缓冲区类型，它与async_read_until的第二个参数不匹配。此重载需要动态缓冲区，只需使用boost::asio::dynamic_buffer。
void on_write(const error_code & err, std::size_t bytes) {
write(out, buffer("$ "));
async_read_until(in, dynamic_buffer(line),'\n',on_read);
}
int main() {
async_read_until(in, dynamic_buffer(line),'\n',on_read);
ioservice.run();
}