我会看一下boost::iostreams::mapped_file,但我认为我的要求更简单。我已经创建了一个从basic_filebuf派生的自定义类。
template<typename char_type>
class basic_filemultibuf : public std::basic_filebuf<char_type>
{
private:
char_type** m_buffers;
std::ptrdiff_t m_buffer_count,
m_curent_buffer;
std::streamsize m_buffer_size;
protected:
virtual int_type overflow(int_type meta = traits_type::eof())
{
if (this->m_buffer_count > 0)
{
if (this->m_curent_buffer == this->m_buffer_count)
this->m_curent_buffer = 0;
this->basic_filebuf::setbuf(this->m_buffers[this->m_curent_buffer++], this->m_buffer_size);
}
return this->basic_filebuf::overflow(meta);
}
public:
basic_filemultibuf(basic_filebuf const& other)
: basic_filebuf(other),
m_buffers(NULL),
m_buffer_count(0),
m_curent_buffer(-1),
m_buffer_size(0)
{
}
basic_filemultibuf(basic_filemultibuf const& other)
: basic_filebuf(other),
m_buffers(other.m_buffers),
m_buffer_count(other.m_buffer_count),
m_curent_buffer(other.m_curent_buffer),
m_buffer_size(other.m_buffer_size)
{
}
basic_filemultibuf(FILE* f = NULL)
: basic_filemultibuf(basic_filebuf(f))
{
}
basic_filemultibuf* pubsetbuf(char** buffers, std::ptrdiff_t buffer_count, std::streamsize buffer_size)
{
if ((this->m_buffers = buffers) != NULL)
{
this->m_buffer_count = buffer_count;
this->m_buffer_size = buffer_size;
this->m_curent_buffer = 0;
}
else
{
this->m_buffer_count = 0;
this->m_buffer_size = 0;
this->m_curent_buffer = -1;
}
this->basic_filebuf::setbuf(NULL, 0);
return this;
}
};
使用示例:
typedef basic_filemultibuf<char> filemultibuf;
std::fstream file("file", std::ios_base::binary | std::ios_base::in | std::ios_base::out);
char** buffers = new char*[2];
for (int i = 0; i < n; ++i)
buffers[i] = new char[4096];
filemultibuf multibuf(*file.rdbuf());
multibuf.pubsetbuf(buffers, 2, 4096);
file.set_rdbuf(&multibuf);
for (int i = 0; i < n; ++i)
delete[] buffers[i];
基本上就是这样了。我唯一想做的事情就是为其他streambufs提供这个功能,因为使用多个缓冲区不应该仅限于filebuf。但在我看来,如果没有重写特定于文件的函数,这似乎是不可能的。
你对此有何看法?