c++ 要包含哪些文件和库？

Question

Many times I find useful code examples on the Internet. About half of the time they don't specify what files to include or even what libs to include on the command line with -l. How do you usually find that out?

edit note: The problem below has been solved. The remainder of this post can be skipped.

Right now, I'm getting tons of errors while trying to compile:

53: string Gunzip::gunzip(string& compressed)
54: {
55:   namespace io = boost::iostreams;
56:
57:   io::filtering_istream gunzip;
58:   gunzip.push(io::gzip_decompressor());
59:   std::istringstream in_stream = std::istringstream(compressed);
60:   gunzip.push(in_stream);
61:
62:   stringstream strstream;
63:   io::copy(gunzip, strstream);
64:   return strstream.str();
65: }

After a day on the Internet I'm trying:

option: 3 -L/usr/include/boost
and:
 8: #include <string>
 9: #include <iostream>
10: #include <sstream>

15: #include <boost/iostreams/copy.hpp>
16: #include <boost/iostreams/device/array.hpp>
17: #include <boost/iostreams/device/back_inserter.hpp>
18: #include <boost/iostreams/filter/gzip.hpp>
19: #include <boost/iostreams/filter/test.hpp>
20: #include <boost/iostreams/filtering_stream.hpp>

The error I have is:

                 from /usr/include/c++/4.5/string:45,
                 from Gunzip.cpp:8:
/usr/include/c++/4.5/bits/ios_base.h: In copy constructor     ‘std::basic_ios<char>::basic_ios(const std::basic_ios<char>&)’:
In file included from /usr/include/c++/4.5/bits/localefwd.h:43:0,
/usr/include/c++/4.5/bits/ios_base.h:785:5: error: ‘std::ios_base::ios_base(const     std::ios_base&)’ is private
/usr/include/c++/4.5/iosfwd:77:11: error: within this context
/usr/include/c++/4.5/iosfwd: In copy constructor     ‘std::basic_istringstream<char>::basic_istringstream(const     std::basic_istringstream<char>&)’:
/usr/include/c++/4.5/iosfwd:97:11: note: synthesized method     ‘std::basic_ios<char>::basic_ios(const std::basic_ios<char>&)’ first required here 
/usr/include/c++/4.5/streambuf: In copy constructor     ‘std::basic_stringbuf<char>::basic_stringbuf(const std::basic_stringbuf<char>&)’:
/usr/include/c++/4.5/streambuf:773:7: error: ‘std::basic_streambuf<_CharT,     _Traits>::basic_streambuf(const std::basic_streambuf<_CharT, _Traits>::__streambuf_type&)     [with _CharT = char, _Traits = std::char_traits<char>, std::basic_streambuf<_CharT,     _Traits>::__streambuf_type = std::basic_streambuf<char>]’ is private
/usr/include/c++/4.5/iosfwd:93:11: error: within this context
/usr/include/c++/4.5/iosfwd: In copy constructor     ‘std::basic_istringstream<char>::basic_istringstream(const     std::basic_istringstream<char>&)’:
/usr/include/c++/4.5/iosfwd:97:11: note: synthesized method     ‘std::basic_stringbuf<char>::basic_stringbuf(const std::basic_stringbuf<char>&)’ first     required here 
Gunzip.cpp: In member function ‘std::string Gunzip::gunzip(std::string&)’:
Gunzip.cpp:59:65: note: synthesized method     ‘std::basic_istringstream<char>::basic_istringstream(const std::basic_istringstream<char>&)’ first required here 
make[2]: Leaving directory `/home/albert/NetBeansProjects/Arb3'
make[1]: Leaving directory `/home/albert/NetBeansProjects/Arb3'
make[2]: *** [build/Debug/GNU-Linux-x86/Gunzip.o] Error 1
make[1]: *** [.build-conf] Error 2
make: *** [.build-impl] Error 2

BUILD FAILED (exit value 2, total time: 9s)

I can remove the first 3 includes to obtain other errors I don't understand. I don't know which errors are better.

1. Is this error related to includes? How should I know? I'm blaming the includes because so far all errors were due to includes. I don't know what basic_ios is.
2. How do you find out what to include and what libs to use?

Answer 1

The error you posted is actually not an include-related error, or a linker error it is the line:

std::istringstream in_stream = std::istringstream(compressed);

that causes a call to an inherited copy constructor that is marked as private, so you should replace it with:

std::istringstream in_stream(compressed);

The compiler output is actually quite clear in this case.

Answer 2

The short answer is 'it depends'. For classes / functions which are part of the C++ standard library the man pages which come with your compiler will list which header(s) and libraries are required; or alternately you can use online resources such as cplusplus.com , MSDN or GNU libstdc++ doxygen docs .

For things like Boost you have to look at their documentation; however the obvious question is 'how do I know if a class is from boost' - to which the answer is pretty much 'Google it' - over time you'll get used to what is and isn't in Boost.

Answer 3

In general if you could not find the required libraries or don't know how to build and use it, the best places to find such information are: the project's docs or wiki page, forum or IRC channel. To find which project the classes/functions belong you can search using the class/function's name.

For the above code snippet you need Boost . Mostly all you need to do is #include the header file. But certain libraries require you to build and link them. See the ' Getting Started on Microsoft Windows ' or ' Getting Started on Unix variants (eg Linux, MacOS) ' for instructions.

If you are working on a Windows machine, you can download the pre-compiled binaries from here: http://www.boostpro.com/download/