从升压filtering_streambuf DECOM preSS文件为std ::矢量＆lt;＆字符GT ;? [英] Decompress file from Boost filtering_streambuf to std::vector<char>?

问题描述

我想DECOM preSS使用deflate算法和东西它变成一个矢＆lt这是COM pressed文件; unsigned char型＆GT; 。从调研至今我所完成的，这似乎是我可以使用的boost ::输入输出流:: filtering_streambuf ，然后用的boost ::输入输出流::复制（）来得到它变成一个的boost ::进程间:: basic_vectorstream＆LT;的std ::矢量＆lt; unsigned char型＆GT;＆GT; ，然后拉底层矢量出vectorstream的。不过，我得到一吨的编译器错误的，首先是这样的：

I'm trying to decompress a file that was compressed using the DEFLATE algorithm and stuff it into a vector<unsigned char>. From the research I've done so far, it seemed like I could use a boost::iostreams::filtering_streambuf and then use boost::iostreams::copy() to get it into a boost::interprocess::basic_vectorstream<std::vector<unsigned char>> and then pull the underlying vector out of the vectorstream. However, I'm getting a ton of compiler errors, starting with this:

/usr/include/boost/iostreams/copy.hpp: In function ‘std::streamsize boost::iostreams::detail::copy_impl(Source, Sink, std::streamsize) [with Source = boost::reference_wrapper<boost::iostreams::filtering_streambuf<boost::iostreams::input> >, Sink = boost::reference_wrapper<boost::interprocess::basic_vectorstream<std::vector<unsigned char> > >, std::streamsize = long int]’:
/usr/include/boost/iostreams/copy.hpp:245:79:   instantiated from ‘std::streamsize boost::iostreams::copy(Source&, Sink&, std::streamsize, typename boost::enable_if<boost::iostreams::is_std_io<Source> >::type*, typename boost::enable_if<boost::iostreams::is_std_io<Sink> >::type*) [with Source = boost::iostreams::filtering_streambuf<boost::iostreams::input>, Sink = boost::interprocess::basic_vectorstream<std::vector<unsigned char> >, std::streamsize = long int, typename boost::enable_if<boost::iostreams::is_std_io<Source> >::type = void, typename boost::enable_if<boost::iostreams::is_std_io<Sink> >::type = void]’
ValueFileReader.cpp:92:41:   instantiated from here
/usr/include/boost/iostreams/copy.hpp:178:5: error: static assertion failed: "(is_same<src_char, snk_char>::value)"

在code我用低于（简称和使用命名空间为简便起见在这里做）：

The code I'm using is below (shortened up and doing "using namespace" for brevity here):

using namespace boost::iostreams;
using namespace boost::interprocess;

filtering_streambuf<input> in;
std::ifstream file(filename, std::ifstream::in);
in.push(zlib_decompressor());
in.push(file);

basic_vectorstream<std::vector<unsigned char>> vectorStream;
copy(in, vectorStream);
std::vector<unsigned char> chars(vectorStream.vector());

我见过的<一个href=\"http://stackoverflow.com/questions/9557555/how-can-i-decom$p$pss-a-vector-of-deflated-data-with-boost\">this螺纹，但我不知道，如果将所有内容复制到一个载体，然后DECOM pressing从载体将是绕了最有效的方式。

I've seen this thread, but I wasn't sure if copying everything into a vector, then decompressing from the vector would be the most efficient way of going about it.

有没有更好的办法，我可以去吗，或者我有个好主意，但在code一些错误？

Is there a better way I can go about this, or do I have the right idea but some error in the code?

推荐答案

的问题是，你的 ifstream的和 filtering_streambuf 使用字符作为其基础字符类型，但你的 basic_vectorstream 使用 unsigned char型作为它的值类型。升压code有一个静态断言要求这些类型是一样的，所以，如果你使用两种不同类型的不可转换你没有得到编译器错误的溢料。

The problem is that your ifstream and filtering_streambuf use char as their underlying character type, but your basic_vectorstream uses unsigned char as its value type. The Boost code has a static assertion requiring that these types be the same so that you don't get a spew of compiler errors if you use two different types that are not convertible.

幸运的是，这里的修复是很容易与ndash的;变化：

Fortunately, the fix here is easy – change:

basic_vectorstream<std::vector<unsigned char>> vectorStream;
copy(in, vectorStream);
std::vector<unsigned char> chars(vectorStream.vector());

到

basic_vectorstream<std::vector<char>> vectorStream;
copy(in, vectorStream);
std::vector<unsigned char> chars(
    vectorStream.vector().begin(),
    vectorStream.vector().end()
);

这是安全的，因为字符和 unsigned char型是由C ++标准保证具有相同的对象重新presentation（§3.9.1/ 1）。

This is safe because char and unsigned char are guaranteed by the C++ standard to have the same object representation (§3.9.1/1).

无关于直接的问题，但你也需要通过的std :: IOS ::二进制到文件的构造函数，否则你将不得不因行结束转换损坏的数据。

Unrelated to your direct problem, but you also need to pass std::ios::binary to file's constructor, otherwise you'll have corrupt data due to line-ending conversions.

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