How do I convert a string to a wstring using the value of the string?

This is in reference to the most up-voted answer but I don't have enough "reputation" to just comment directly on the answer.

The name of the function in the solution "wstring_from_bytes" implies it is doing what the original poster wants, which is to get a wstring given a string, but the function is actually doing the opposite of what the original poster asked for and would more accurately be named "bytes_from_wstring".

To convert from string to wstring, the wstring_from_bytes function should use mbstowcs not wcstombs

#define _CRT_SECURE_NO_WARNINGS #include <iostream> #include <cstdlib> #include <string> std::wstring wstring_from_bytes(std::string const& str) { size_t requiredSize = 0; std::wstring answer; wchar_t *pWTempString = NULL; /* * Call the conversion function without the output buffer to get the required size * - Add one to leave room for the NULL terminator */ requiredSize = mbstowcs(NULL, str.c_str(), 0) + 1; /* Allocate the output string (Add one to leave room for the NULL terminator) */ pWTempString = (wchar_t *)malloc( requiredSize * sizeof( wchar_t )); if (pWTempString == NULL) { printf("Memory allocation failure.\n"); } else { // Call the conversion function with the output buffer size_t size = mbstowcs( pWTempString, str.c_str(), requiredSize); if (size == (size_t) (-1)) { printf("Couldn't convert string\n"); } else { answer = pWTempString; } } if (pWTempString != NULL) { delete[] pWTempString; } return answer; } int main() { std::string str = "abcd"; std::wstring wstr = wstring_from_bytes(str); } 

Regardless, this is much more easily done in newer versions of the standard library (C++ 11 and newer)

#include <locale> #include <codecvt> #include <string> std::wstring_convert<std::codecvt_utf8_utf16<wchar_t>> converter; std::wstring wide = converter.from_bytes(narrow_utf8_source_string); 

Here is an implementation using wcstombs (Updated):

#include <iostream> #include <cstdlib> #include <string> std::string wstring_from_bytes(std::wstring const& wstr) { std::size_t size = sizeof(wstr.c_str()); char *str = new char[size]; std::string temp; std::wcstombs(str, wstr.c_str(), size); temp = str; delete[] str; return temp; } int main() { std::wstring wstr = L"abcd"; std::string str = wstring_from_bytes(wstr); } 

Here is a demo.

printf-style format specifiers are not part of the C++ library and cannot be used to construct a string.

If the string may only contain single-byte characters, then the range constructor is sufficient.

std::string narrower( "hello" ); std::wstring wider( narrower.begin(), narrower.end() ); 

The problem is that we usually use wstring when wide characters are applicable (hence the w), which are represented in std::string by multibyte sequences. Doing this will cause each byte of a multibyte sequence to translate to an sequence of incorrect wide characters.

Moreover, to convert a multibyte sequence requires knowing its encoding. This information is not encapsulated by std::string nor std::wstring. C++11 allows you to specify an encoding and translate using std::wstring_convert, but I'm not sure how widely supported it is of yet. See 0x....'s excellent answer.

The converter mentioned for C++11 and above has deprecated this specific conversion in C++17, and suggests using the MultiByteToWideChar function.

The compiler error (c4996) mentions defining _SILENCE_CXX17_CODECVT_HEADER_DEPRECATION_WARNING.

wstring temp = L""; for (auto c : DATA_DIR) temp.push_back(c); 

I found this function. Could not find any predefined method to do this.

std::wstring s2ws(const std::string& s) { int len; int slength = (int)s.length() + 1; len = MultiByteToWideChar(CP_ACP, 0, s.c_str(), slength, 0, 0); wchar_t* buf = new wchar_t[len]; MultiByteToWideChar(CP_ACP, 0, s.c_str(), slength, buf, len); std::wstring r(buf); delete[] buf; return r; } std::wstring stemp = s2ws(myString);