How to convert std::stringstream to std::wstring

Question

my question is that how to convert c++ stringstream in wstring or wstringstream

stringstream fileSearch;
fileSearch<<fileOutput.str();
fileSearch<<"*.jpg";
cout<<fileSearch.str()<<endl;

here is my code. i want to convert this fileSearch stringstream into wstring... can some one help me please with c++ example code... i want to use this filesearch stringstream in

int numOfFiles(wstring searchPath);

this function...

The reduced question is, how to convert from a `std::string` to a `std::wstring`. That depends on the encodings used, and hence to some degree on the platform. — Cheers and hth. - Alf, Feb 25 '15 at 06:31
possible duplicate of [How to convert wstring into string?](http://stackoverflow.com/questions/4804298/how-to-convert-wstring-into-string) — Jonathan Potter, Feb 25 '15 at 06:42
@close-voters: the suggested duplicate is about the opposite conversion (and doesn't have a complete answer). — Cheers and hth. - Alf, Feb 25 '15 at 07:44
@qaisar: Sorry it took some time to get it right. I mistakenly believed `ctype::widen` could do the job. But it fails with multibyte encodings (it's just unusable, a silly-function) so now using `mbcstowcs`. — Cheers and hth. - Alf, Feb 25 '15 at 11:26
`std::char_traits` quirk #328: The `n` in `widen` stands for "narrow." — Potatoswatter, Jul 26 '15 at 13:33

Cheers and hth. - Alf · Answer 1 · 2015-02-25T11:20:37.370

The std::stringstream can always be converted to std::string, so the question reduces to how to convert std::string to std::wstring.

If the narrow string encoding points are a subset of the wide string encoding points, then you can simply copy the data over:

const std::string s = ...;
const std::wstring ws( s.begin(), s.end() );

This works for original ASCII and its extension Latin-1 when the wide strings are UTF-16 or UTF-32 encoded.

In practice that means that this simple data copying scheme works for:

Latin-1 in a Western installation of Windows, because Latin-1 is a subset of Windows ANSI Western.
ASCII in other Windows installations and in Unix-land, because the default system narrow encoding is (typically) not an extension of Latin-1.

When the narrow string encoding points are not a subset of the wide string encoding points, some more active conversion must be employed.

The following works when the std::string's encoding is the locale's narrow text encoding, and doesn't contain embedded zero bytes:

#include <iostream>
#include <locale>       // std::locale
#include <locale.h>     // setlocale
#include <stdexcept>    // std::runtime_error
#include <stdlib.h>     // mbstowcs
#include <string>
using namespace std;

auto hopefully( const bool condition ) -> bool { return condition; }
auto fail( const string& message ) -> bool { throw runtime_error( message ); }

auto widened( const string& s, locale const& loc = locale() )
    -> wstring
{
    const int n = s.length();
    if( n == 0 ) { return L""; }

    const int max_wide_encoding_values = (sizeof( wchar_t ) == 2? 2 : 1);
    wstring ws( max_wide_encoding_values*s.length(), L'\0' );

    const auto n_characters_stored = mbstowcs( &ws[0], &s[0], ws.size() );
    hopefully( n_characters_stored != -1 )
        || fail( "mbstowcs failed" );
    ws.resize( n_characters_stored );
    return ws;
}

auto operator<<( wostream& stream, const string& s )
    -> wostream&
{ return stream << s.c_str(); }

auto main() -> int
{
    setlocale( LC_ALL, "" );
    locale::global( locale( "" ) );

    const wstring ws = widened( "Blåbærsyltetøy." );
    for( const wchar_t wc : ws )
    {
        wcout << int( wc ) << ' ';
    }
    wcout << endl;
    wcout << L"Should be 'Blåbærsyltetøy'." << endl;
    wcout << L"Is '" << ws << L"'." << endl;
}

In Ubuntu (in a VirtualBox in Windows) the output is OK:

alf@devubuntu32:~/host/dev/explore/_/so/0244$ g++ foo.cpp -std=c++11
alf@devubuntu32:~/host/dev/explore/_/so/0244$ ./a.out
66 108 229 98 230 114 115 121 108 116 101 116 248 121 46 
Should be 'Blåbærsyltetøy'.
Is 'Blåbærsyltetøy.'.
alf@devubuntu32:~/host/dev/explore/_/so/0244$ ▯

In Windows it's ¹necessary to add some fixup to make the wide stream output work:

#include <io.h>
#include <fcntl.h>
#include <stdio.h>

static const bool _ = []() -> bool
{
    const int fd = _fileno( stdout );
    _setmode( fd, _isatty( fd )? _O_WTEXT : _O_U8TEXT );
    return true;
}();

Then with Visual C++ in Windows the output is

H:\dev\explore\_\so\0244>cl iofix.cpp foo.cpp /Feb
iofix.cpp
foo.cpp
Generating Code...

H:\dev\explore\_\so\0244>b
66 108 229 98 230 114 115 121 108 116 101 116 248 121 46
Should be 'Blåbærsyltetøy'.
Is 'Blåbærsyltetøy.'.

H:\dev\explore\_\so\0244>_

However, with MinGW g++ in Windows the default output is not OK:

H:\dev\explore\_\so\0244>g++ iofix.cpp foo.cpp

H:\dev\explore\_\so\0244>a
66 108 195 165 98 195 166 114 115 121 108 116 101 116 195 184 121 46
Should be 'Blåbærsyltetøy'.
Is 'BlÃ¥bÃ¦rsyltetÃ¸y.'.

H:\dev\explore\_\so\0244>_

And the reason is that the default g++ C++ execution character set is UTF-8, which is not the narrow text encoding specified by the default user's locale in Windows. A simple fix would be to specify the correct execution character set to g++. However, that's only practically possible with distributions of g++ that support those options, and e.g. the Nuwen distribution does not.

^{¹) in Unix-land it worked as-is because the global C++ locale has been set to the user's default locale.}

score 2 · Answer 2 · answered Aug 18 '15 at 13:32

2

In C++ 11 you can use this as well to convert a stringstream to a wstring:

std::wstring stringStream2wstring(std::stringstream& strs)
{
    std::string str = strs.str();
    typedef std::codecvt_utf8<wchar_t> convert_type;
    std::wstring_convert<convert_type, wchar_t> converter;
    return converter.from_bytes(str);
}

Note: the example uses std::codecvt_utf8

answered Aug 18 '15 at 13:32

Merav Kochavi

4,223
2
32
37

Seems to be [depreciated](https://stackoverflow.com/q/42946335) – jrh Apr 01 '21 at 20:09

Merav Kochavi · Answer 3 · 2015-07-27T12:45:15.957

1

A short and simple C++ function for converting a stringstream to a wstring:

std::wstring convertToWString(std::stringstream& from)
{
    std::wstring to;
    string stdString = from.str();
    return to.assign(stdString.begin(), stdString.end());
}

Note: This code is limited to the ASCII subset of values only

edited Jul 27 '15 at 12:45

answered Jul 23 '15 at 12:30

Merav Kochavi

4,223
2
32
37

First, you can't copy a `std::stringstream`. Second, there's no such overload (you're confusing `std::vector::assign`). Third, even if there were such overloaded it wouldn't work for characters beyond ASCII. – edmz Jul 23 '15 at 12:52
**−1** In addition to the problems noted byh "black", (1) `begin` and `end` are functions in C++, not properties, and (2) two subsequent invocations of `str()` refer to different temporary objects. – Cheers and hth. - Alf Jul 23 '15 at 20:33
1

@Cheersandhth.-Alf, Thanks for your comment, I added the '&' and '()', ran the code and it now works as expected. – Merav Kochavi Jul 27 '15 at 10:43
**0** Removed downvote because the problem's fixed. @MeravKochavi: note that how well this works depends on the encoding for `char`-based text. With UTF-8 it's limited to the ASCII subset of values (e.g., Norwegian 'Å' will fail). With Windows 1252 it's limited to the ISO Latin-1 subset (e.g., the Euro symbol '€' will fail). The problem is that the stringstream does not carry information about its encoding. It carries a lot of other irrelevant information though. – Cheers and hth. - Alf Jul 27 '15 at 12:29
@Cheersandhth.-Alf, I added your comment on the ASCII limitation to the answer. – Merav Kochavi Jul 27 '15 at 12:46
1

@MeravKochavi, let's get that stain off this post since you clearly corrected it and it is a solution. Thank you for taking corrective actions and adding notes – Damian Dec 14 '18 at 19:58

score 1 · Answer 4 · answered Jul 26 '18 at 23:03

1

#include <boost\lexical_cast.hpp>
stringstream ss;    
std::wstring convertedStr = boost::lexical_cast<std::wstring>(ss);

answered Jul 26 '18 at 23:03

Urvashi Gupta

444
4
13

Please add an explanation of your code, it will greatly increase the quality of the answer. – Nic3500 Jul 27 '18 at 00:11

How to convert std::stringstream to std::wstring

4 Answers4