Seek 不适用于使用 boost filtering_istreambuf初始化的 std：：istream

我试图读取文件。它应该是内存映射以提高性能。我想使用 iostream 的提升过滤器链轻松包含 zip、bzip2 和 gzip 解压缩。

我尝试采用使用 boost：：iostreams mapped_file_source 和 filtering_streambuf 解压缩文件中提出的解决方案。

我的问题：当我尝试在流上seek()时，我得到一个异常："没有随机访问"。这很奇怪，因为从文档中我了解到我可以将std::istream用作接口。

我想出了以下代码(也在coliru上(：

#include <iostream>
#include <stdio.h>
#include <boost/iostreams/device/mapped_file.hpp>
#include <boost/iostreams/stream.hpp>
#include <boost/iostreams/filtering_streambuf.hpp>
// and later also include ...
//#include <boost/iostreams/filter/gzip.hpp>
//#include <boost/iostreams/filter/bzip2.hpp>
int main()
{
    namespace io = boost::iostreams;
    io::mapped_file_source inputDevice;                           // the device to read from (file)
    io::stream<io::mapped_file_source> mappedFileStream; // the memory mapped file stream    
    io::filtering_istreambuf filteredInputStream;                 // the source file (stream), together with a chain of filters and/or decompressors

    inputDevice = io::mapped_file_source("main.cpp");
    mappedFileStream.open(inputDevice);      // open device as a readable stream
    // add optional filter/decoder/decompressor
    //filteredInputStream.push(io::bzip2_decompressor());
    //filteredInputStream.push(io::zlib_decompressor());
    //filteredInputStream.push(io::gzip_decompressor());
    //filteredInputStream.push(io::base64_decoder());
    filteredInputStream.push(mappedFileStream);  //finally add the readable stream 
    // now we have a device that is streamed and the contents are filtered the resulting stream can be used like a std::iostream. (in theory)
    std::istream inputStream(&filteredInputStream);
    std::cout << inputStream.get() << std::endl;
    std::cout << inputStream.get() << std::endl;
    //fatal error: class boost::exception_detail::clone_impl<struct boost::exception_detail::error_info_injector<class std::ios_base::failure> >: no random access
    filteredInputStream.pubseekoff(0, std::ios_base::beg, std::ios_base::in | std::ios_base::out);
    inputStream.seekg(0);  // fatal error: class boost::exception_detail::clone_impl<struct boost::exception_detail::error_info_injector<class std::ios_base::failure> >: no random access
    std::cout << inputStream.get() << std::endl;
    std::cout << inputStream.get() << std::endl;
    return 0;
}