Using boost program_options fails with weird compilation error

Question

I´m trying to use Boost´s program_options library to build a simple command line app to a library but it is failing with a really weird error. Here´s all the code in question (yes, it´s really simple):

#include <iostream>
#include <stdexcept>
#include <string>
#include <boost/program_options.hpp>
#include "NCDocEngineInterop.h"
#include "NCDocumentEngine.h"
#include "NCConfigurationManager.h"
#include "NCAcquisitions.h"

namespace po = boost::program_options;
using std::cout;
using std::cerr;
using std::endl;
using std::domain_error;
using std::wstring;

void fail_if_empty(const po::variables_map& variables, const char* field) {
    if (!(variables.count(field))) {
        cerr << field << " is required, you must provide a value for it" << endl;
        throw domain_error(field);
    }
}

int main(int ac, char* av[])
{

    const char* nsdk_path_option = "nsdk-path"; // NC_CONFIGURATION::NC_NSDK_PATH
    const char* ocr_path_option = "ocr-path"; // NC_CONFIGURATION::NC_OCR_PATH
    const char* parser_path_option = "parser-path-option"; // NC_CONFIGURATION::NC_PARSER_PATH
    const char* pdf_path = "pdf-path"; // NC_CONFIGURATION::NC_PDF_PATH
    const char* output_directory = "output-directory";
    const char* input_file = "input-file";

    po::options_description description("Runs the NDSK engine at the provided files");
    description.add_options()  
        ("help", "produce help message")
        (nsdk_path_option, po::value<wstring>(), "path to the NSDK")
        (ocr_path_option, po::value<wstring>(), "path to the OCR")
        (parser_path_option, po::value<wstring>(), "path to the parser")
        (pdf_path, po::value<wstring>(),"path to the PDF processor")
        (output_directory, po::value<wstring>(), "path to the folder where the output will be stored")
        (input_file, po::value<wstring>(), "path to the input file")
    ;

    po::variables_map vm;
    po::store(po::parse_command_line(ac, av, description), vm);
    po::notify(vm);

    fail_if_empty(vm, nsdk_path_option);
    fail_if_empty(vm, ocr_path_option);
    fail_if_empty(vm, parser_path_option);
    fail_if_empty(vm, pdf_path);
    fail_if_empty(vm, output_directory);
    fail_if_empty(vm, input_file);

    NCConfigurationManager::ncSetConfiguration(
        NC_NSDK_PATH, 
        vm[nsdk_path_option].as<wstring>() );
    NCConfigurationManager::ncSetConfiguration(
        NC_OCR_PATH,
        vm[ocr_path_option].as<wstring>() );
    NCConfigurationManager::ncSetConfiguration(
        NC_PARSER_PATH,
        vm[parser_path_option].as<wstring>() );
    NCConfigurationManager::ncSetConfiguration(
        NC_PDF_PATH,
        vm[pdf_path].as<wstring>() );

    return 0;
}

The compilation error that happens is:

Error error C2679: binary '<<' : no operator found which takes a right-hand operand of type 'const src' (or there is no acceptable conversion) c:\work\dev\source\src\framework\thirdparty\boost\boost\lexical_cast.hpp 1281 1 DocumentProcessor

Error error C2228: left of '.fail' must have class/struct/union c:\work\digitalbp\projects\releasedev\nsdk_4_0\dev\source\src\framework\thirdparty\boost\boost\lexical_cast.hpp 1281 1 DocumentProcessor

You can see the lexical_cast.hpp file here.

And I have no idea what´s going on here or why this error is happening for this code. I am using boost 1.50.0 and I can´t upgrade it now. I´m also using Visual Studio 2010 to build it.

And here´s the output of the Output window:

1>c:\work\src\framework\thirdparty\boost\boost\lexical_cast.hpp(1281): error C2679: binary '<<' : no operator found which takes a right-hand operand of type 'const src' (or there is no acceptable conversion)
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\ostream(679): could be 'std::basic_ostream<_Elem,_Traits> &std::operator <<<wchar_t,std::char_traits<wchar_t>>(std::basic_ostream<_Elem,_Traits> &,const char *)' [found using argument-dependent lookup]
1>          with
1>          [
1>              _Elem=wchar_t,
1>              _Traits=std::char_traits<wchar_t>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\ostream(726): or       'std::basic_ostream<_Elem,_Traits> &std::operator <<<wchar_t,std::char_traits<wchar_t>>(std::basic_ostream<_Elem,_Traits> &,char)' [found using argument-dependent lookup]
1>          with
1>          [
1>              _Elem=wchar_t,
1>              _Traits=std::char_traits<wchar_t>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\ostream(968): or       'std::basic_ostream<_Elem,_Traits> &std::operator <<<wchar_t,std::char_traits<wchar_t>,const InputStreamable>(std::basic_ostream<_Elem,_Traits> &&,_Ty)' [found using argument-dependent lookup]
1>          with
1>          [
1>              _Elem=wchar_t,
1>              _Traits=std::char_traits<wchar_t>,
1>              InputStreamable=src,
1>              _Ty=src
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\ostream(1085): or       'std::basic_ostream<_Elem,_Traits> &std::operator <<<wchar_t,std::char_traits<wchar_t>>(std::basic_ostream<_Elem,_Traits> &,const std::error_code &)' [found using argument-dependent lookup]
1>          with
1>          [
1>              _Elem=wchar_t,
1>              _Traits=std::char_traits<wchar_t>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\ostream(186): or       'std::basic_ostream<_Elem,_Traits> &std::basic_ostream<_Elem,_Traits>::operator <<(std::basic_ostream<_Elem,_Traits> &(__cdecl *)(std::basic_ostream<_Elem,_Traits> &))'
1>          with
1>          [
1>              _Elem=wchar_t,
1>              _Traits=std::char_traits<wchar_t>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\ostream(192): or       'std::basic_ostream<_Elem,_Traits> &std::basic_ostream<_Elem,_Traits>::operator <<(std::basic_ios<_Elem,_Traits> &(__cdecl *)(std::basic_ios<_Elem,_Traits> &))'
1>          with
1>          [
1>              _Elem=wchar_t,
1>              _Traits=std::char_traits<wchar_t>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\ostream(199): or       'std::basic_ostream<_Elem,_Traits> &std::basic_ostream<_Elem,_Traits>::operator <<(std::ios_base &(__cdecl *)(std::ios_base &))'
1>          with
1>          [
1>              _Elem=wchar_t,
1>              _Traits=std::char_traits<wchar_t>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\ostream(206): or       'std::basic_ostream<_Elem,_Traits> &std::basic_ostream<_Elem,_Traits>::operator <<(std::_Bool)'
1>          with
1>          [
1>              _Elem=wchar_t,
1>              _Traits=std::char_traits<wchar_t>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\ostream(226): or       'std::basic_ostream<_Elem,_Traits> &std::basic_ostream<_Elem,_Traits>::operator <<(short)'
1>          with
1>          [
1>              _Elem=wchar_t,
1>              _Traits=std::char_traits<wchar_t>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\ostream(260): or       'std::basic_ostream<_Elem,_Traits> &std::basic_ostream<_Elem,_Traits>::operator <<(unsigned short)'
1>          with
1>          [
1>              _Elem=wchar_t,
1>              _Traits=std::char_traits<wchar_t>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\ostream(280): or       'std::basic_ostream<_Elem,_Traits> &std::basic_ostream<_Elem,_Traits>::operator <<(int)'
1>          with
1>          [
1>              _Elem=wchar_t,
1>              _Traits=std::char_traits<wchar_t>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\ostream(305): or       'std::basic_ostream<_Elem,_Traits> &std::basic_ostream<_Elem,_Traits>::operator <<(unsigned int)'
1>          with
1>          [
1>              _Elem=wchar_t,
1>              _Traits=std::char_traits<wchar_t>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\ostream(325): or       'std::basic_ostream<_Elem,_Traits> &std::basic_ostream<_Elem,_Traits>::operator <<(long)'
1>          with
1>          [
1>              _Elem=wchar_t,
1>              _Traits=std::char_traits<wchar_t>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\ostream(345): or       'std::basic_ostream<_Elem,_Traits> &std::basic_ostream<_Elem,_Traits>::operator <<(unsigned long)'
1>          with
1>          [
1>              _Elem=wchar_t,
1>              _Traits=std::char_traits<wchar_t>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\ostream(366): or       'std::basic_ostream<_Elem,_Traits> &std::basic_ostream<_Elem,_Traits>::operator <<(__int64)'
1>          with
1>          [
1>              _Elem=wchar_t,
1>              _Traits=std::char_traits<wchar_t>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\ostream(386): or       'std::basic_ostream<_Elem,_Traits> &std::basic_ostream<_Elem,_Traits>::operator <<(unsigned __int64)'
1>          with
1>          [
1>              _Elem=wchar_t,
1>              _Traits=std::char_traits<wchar_t>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\ostream(407): or       'std::basic_ostream<_Elem,_Traits> &std::basic_ostream<_Elem,_Traits>::operator <<(float)'
1>          with
1>          [
1>              _Elem=wchar_t,
1>              _Traits=std::char_traits<wchar_t>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\ostream(427): or       'std::basic_ostream<_Elem,_Traits> &std::basic_ostream<_Elem,_Traits>::operator <<(double)'
1>          with
1>          [
1>              _Elem=wchar_t,
1>              _Traits=std::char_traits<wchar_t>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\ostream(447): or       'std::basic_ostream<_Elem,_Traits> &std::basic_ostream<_Elem,_Traits>::operator <<(long double)'
1>          with
1>          [
1>              _Elem=wchar_t,
1>              _Traits=std::char_traits<wchar_t>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\ostream(467): or       'std::basic_ostream<_Elem,_Traits> &std::basic_ostream<_Elem,_Traits>::operator <<(const void *)'
1>          with
1>          [
1>              _Elem=wchar_t,
1>              _Traits=std::char_traits<wchar_t>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\ostream(487): or       'std::basic_ostream<_Elem,_Traits> &std::basic_ostream<_Elem,_Traits>::operator <<(std::basic_streambuf<_Elem,_Traits> *)'
1>          with
1>          [
1>              _Elem=wchar_t,
1>              _Traits=std::char_traits<wchar_t>
1>          ]
1>          while trying to match the argument list '(std::basic_ostringstream<_Elem,_Traits,_Alloc>, const src)'
1>          with
1>          [
1>              _Elem=wchar_t,
1>              _Traits=std::char_traits<wchar_t>,
1>              _Alloc=std::allocator<wchar_t>
1>          ]
1>          c:\work\src\framework\thirdparty\boost\boost\lexical_cast.hpp(1499) : see reference to function template instantiation 'bool boost::detail::lexical_stream_limited_src<CharT,Traits,RequiresStringbuffer>::shl_input_streamable<const InStreamable>(InputStreamable &)' being compiled
1>          with
1>          [
1>              CharT=char_type,
1>              Traits=traits,
1>              RequiresStringbuffer=true,
1>              InStreamable=src,
1>              InputStreamable=src
1>          ]
1>          c:\work\src\framework\thirdparty\boost\boost\lexical_cast.hpp(1974) : see reference to function template instantiation 'bool boost::detail::lexical_stream_limited_src<CharT,Traits,RequiresStringbuffer>::operator <<<Source>(const InStreamable &)' being compiled
1>          with
1>          [
1>              CharT=char_type,
1>              Traits=traits,
1>              RequiresStringbuffer=true,
1>              Source=src,
1>              InStreamable=src
1>          ]
1>          c:\work\src\framework\thirdparty\boost\boost\lexical_cast.hpp(1921) : while compiling class template member function 'std::wstring boost::detail::lexical_cast_do_cast<Target,Source>::lexical_cast_impl(const Source &)'
1>          with
1>          [
1>              Target=std::wstring,
1>              Source=src
1>          ]
1>          c:\work\src\framework\thirdparty\boost\boost\lexical_cast.hpp(2133) : see reference to class template instantiation 'boost::detail::lexical_cast_do_cast<Target,Source>' being compiled
1>          with
1>          [
1>              Target=std::wstring,
1>              Source=src
1>          ]
1>          c:\work\src\framework\thirdparty\boost\boost\program_options\detail\value_semantic.hpp(89) : see reference to function template instantiation 'Target boost::lexical_cast<T,std::basic_string<_Elem,_Traits,_Ax>>(const Source &)' being compiled
1>          with
1>          [
1>              Target=std::wstring,
1>              T=std::wstring,
1>              _Elem=char,
1>              _Traits=std::char_traits<char>,
1>              _Ax=std::allocator<char>,
1>              Source=std::basic_string<char,std::char_traits<char>,std::allocator<char>>
1>          ]
1>          c:\work\src\framework\thirdparty\boost\boost\program_options\detail\value_semantic.hpp(170) : see reference to function template instantiation 'void boost::program_options::validate<T,char>(boost::any &,const std::vector<_Ty> &,T *,long)' being compiled
1>          with
1>          [
1>              T=std::wstring,
1>              _Ty=std::string
1>          ]
1>          c:\work\src\framework\thirdparty\boost\boost\program_options\detail\value_semantic.hpp(163) : while compiling class template member function 'void boost::program_options::typed_value<T,charT>::xparse(boost::any &,const std::vector<_Ty> &) const'
1>          with
1>          [
1>              T=std::wstring,
1>              charT=char,
1>              _Ty=std::string
1>          ]
1>          c:\work\src\samples\cpp\documentprocessor\documentprocessor\main.cpp(37) : see reference to class template instantiation 'boost::program_options::typed_value<T,charT>' being compiled
1>          with
1>          [
1>              T=std::wstring,
1>              charT=char
1>          ]
1>c:\work\src\framework\thirdparty\boost\boost\lexical_cast.hpp(1281): error C2228: left of '.fail' must have class/struct/union
========== Rebuild All: 0 succeeded, 1 failed, 0 skipped ==========

Answer 1

The problem is actually here:

po::store(po::parse_command_line(ac, av, description), vm);

parse_command_line instanciates a basic_command_line_parser<charT> where charT is of course char, not wchar_t, because av is of type char**. This means that all strings in the options_description are necessarily basic_string<char>, i.e. std::string and not std::wstring.

This actually makes sense if you think about it, since command line options always arrive as plain old "c" strings. Even if they were mbcs-encoded it would be your responsibility to perform the conversion using the correct locale. This unfortunately is necessary because interpretation of MBCS is locale-specific.

I had a look to see if it's possible to create a wchar_t version of options_description (in case you wanted to use it from wmain() but it's not. options_description contains hardcoded std::strings.

multi-byte strings reference