How to transfer Russian characters to _wsystem (c++ windows)?

Question

Command line

Good afternoon!
Yes:
windows 7
gcc 5.1
c++ 11
asio
websocketpp
grep.
Required:
Call the grep command, which transmits Russian letters over the network using websocketpp (asio).
Please advise how this can be implemented.
I tried it through the _wsystem function, which I directly passed "grep \"<Russian characters>\" <filename>". That's how everything works. But when I convert a string coming from websocketpp and write it to another one, I get abracadabra.
I convert like this:

std::ostringstream cmdStr;
//переменная from_websocketpp имеет тип std::string
cmdStr << "grep \"" << from_websocketpp << "\" filename.txt>grep.txt";
std::string cmdStr_res = cmdStr.str();

size_t newsize = strlen(cmdStr_res.c_str()) + 1;
wchar_t * wcstring = new wchar_t[newsize];
size_t convertedChars = 0;
mbstowcs_s(&convertedChars, wcstring, newsize, cmdStr_res.c_str(), _TRUNCATE);
_wsystem(wcstring);

UPD1
Here is the output in the console
UPD2
Solved the problem by writing, reading to an intermediate file using std::ofstream and std::ifstream.
Thanks for the hints.

Answer 1

Fuck system/_wsystem
www.highscore.de/boost/process/process/tutorials.html

Answer 2

In my opinion, it's ok. If it does not work, then you need to look under the debugger, what kind of characters are obtained there.
Is the input UTF-8, or something else?
PS It is not clear why it is so difficult:
instead of
cmdStr_res.length()