Asio基本接口

Asio是C++的网络库，有boost和非boost这两种版本，这里涉及的都是非boost的版本。Asio官方文档

在使用Asio时可以只包含头文件asio.hpp，如果知道所用接口具体在哪个头文件中定义，也可以直接包含该头文件。

buffer

头文件asio/buffer.hpp

asio::buffer的接口很多，下面这些都是：

mutable_buffers_1 buffer(const mutable_buffer & b);
mutable_buffers_1 buffer(const mutable_buffer & b, std::size_t max_size_in_bytes);
const_buffers_1 buffer(const const_buffer & b);
const_buffers_1 buffer(const const_buffer & b, std::size_t max_size_in_bytes);
mutable_buffers_1 buffer(void * data, std::size_t size_in_bytes);
const_buffers_1 buffer(const void * data, std::size_t size_in_bytes);
// 模板
template< typename PodType, std::size_t N> 
mutable_buffers_1 buffer( PodType (&data)[N]);

template<typename PodType, std::size_t N>
mutable_buffers_1 buffer(PodType (&data)[N], std::size_t max_size_in_bytes);

template<typename PodType, std::size_t N>
const_buffers_1 buffer(const PodType (&data)[N]);

template<typename PodType, std::size_t N>
const_buffers_1 buffer(const PodType (&data)[N], std::size_t max_size_in_bytes);

template<typename PodType, std::size_t N>
mutable_buffers_1 buffer(boost::array< PodType, N > & data);

template<typename PodType, std::size_t N>
mutable_buffers_1 buffer(boost::array< PodType, N > & data, std::size_t max_size_in_bytes);

template<typename PodType, std::size_t N>
const_buffers_1 buffer(boost::array< const PodType, N > & data);

template<typename PodType, std::size_t N>
const_buffers_1 buffer(boost::array< const PodType, N > & data, std::size_t max_size_in_bytes);

template<typename PodType, std::size_t N>
const_buffers_1 buffer(const boost::array< PodType, N > & data);

template<typename PodType, std::size_t N>
const_buffers_1 buffer(const boost::array< PodType, N > & data, std::size_t max_size_in_bytes);

template<typename PodType, std::size_t N>
mutable_buffers_1 buffer(std::array< PodType, N > & data);

template<typename PodType, std::size_t N>
mutable_buffers_1 buffer(std::array< PodType, N > & data, std::size_t max_size_in_bytes);

template<typename PodType, std::size_t N>
const_buffers_1 buffer(std::array< const PodType, N > & data);

template<typename PodType, std::size_t N>
const_buffers_1 buffer(std::array< const PodType, N > & data, std::size_t max_size_in_bytes);

template<typename PodType, std::size_t N>
const_buffers_1 buffer(const std::array< PodType, N > & data);

template<typename PodType, std::size_t N>
const_buffers_1 buffer(const std::array< PodType, N > & data, std::size_t max_size_in_bytes);

template<typename PodType, typename Allocator>
mutable_buffers_1 buffer(std::vector< PodType, Allocator > & data);

template<typename PodType, typename Allocator>
mutable_buffers_1 buffer(std::vector< PodType, Allocator > & data, std::size_t max_size_in_bytes);

template<typename PodType, typename Allocator>
const_buffers_1 buffer(const std::vector< PodType, Allocator > & data);

template<typename PodType, typename Allocator>
const_buffers_1 buffer(const std::vector< PodType, Allocator > & data, std::size_t max_size_in_bytes);

template<typename Elem, typename Traits, typename Allocator>
const_buffers_1 buffer(const std::basic_string< Elem, Traits, Allocator > & data);

template<typename Elem, typename Traits, typename Allocator>
const_buffers_1 buffer(const std::basic_string< Elem, Traits, Allocator > & data, std::size_t max_size_in_bytes);

一般常用的是这几个：

mutable_buffers_1 buffer(void * data, std::size_t size_in_bytes);

一般用带有指定大小的比较方便，这样可以重复利用buffer，不需要去整一个恰好大小的buffer。

官方的例子：

char d1[128];
size_t bytes_transferred = sock.receive(asio::buffer(d1));

std::vector<char> d2(128);
bytes_transferred = sock.receive(asio::buffer(d2));

std::array<char, 128> d3;
bytes_transferred = sock.receive(asio::buffer(d3));

boost::array<char, 128> d4;
bytes_transferred = sock.receive(asio::buffer(d4));

注意，如果用的是STL容器，如vector，虽然它是可以动态调整大小的，但是buffer不会去调整它，所以传进去的vector的size决定了这个buffer所能容纳的数据量，而不是capacity决定的。buffer的其他接口还有buffer_size获取大小、buffer_cast类型转换、buffer_copy拷贝，这里不谈了。

write

写的接口比较少，只有如下四个：

template<typename AsyncWriteStream, typename ConstBufferSequence, typename WriteHandler>
void-or-deduced async_write(AsyncWriteStream & s, const ConstBufferSequence & buffers, WriteHandler handler);

template<typename AsyncWriteStream, typename ConstBufferSequence, typename CompletionCondition, typename WriteHandler>
void-or-deduced async_write(AsyncWriteStream & s, const ConstBufferSequence & buffers, CompletionCondition completion_condition, WriteHandler handler);

template<typename AsyncWriteStream, typename Allocator, typename WriteHandler>
void-or-deduced async_write(AsyncWriteStream & s, basic_streambuf< Allocator > & b, WriteHandler handler);

template<typename AsyncWriteStream, typename Allocator, typename CompletionCondition, typename WriteHandler>
void-or-deduced async_write(AsyncWriteStream & s, basic_streambuf< Allocator > & b, CompletionCondition completion_condition, WriteHandler handler);

一般可以这样用：

char data[size] = ...;
asio::async_write(sock, asio::buffer(data, size), handler);