you can convert a std::wstring to a const wchar_t * using the c_str member function

#include <cstdlib>

// ...

std::wstring wStr;
const wchar_t *input = wStr.c_str();

// Count required buffer size (plus one for null-terminator).
size_t size = (wcslen(input) + 1) * sizeof(wchar_t);
char *buffer = new char[size];

#ifdef __STDC_LIB_EXT1__
    // wcstombs_s is only guaranteed to be available if __STDC_LIB_EXT1__ is defined
    size_t convertedSize;
    std::wcstombs_s(&convertedSize, buffer, size, input, size);
#else
    std::wcstombs(buffer, input, size);
#endif

/* Use the string stored in "buffer" variable */

// Free allocated memory:
delete buffer;