Cant compare wide characters | C++ - c++

Question

If I read special characters from a file and then try to compare them (like with an if) it doesn't recognize them.
std::wstring c;
std::wifstream file;
file.open("test.txt");
while (file)
{
wchar_t tmp = file.get();
c += tmp;
}
file.close();
size_t l = c.length();
for (int i = 0; i < l; i++)
{
wchar_t a = c[i];
if (a == L'ä') {
std::cout << "if triggered.";
}
}
But when I create a wchar and predefine a special character it does work.
wchar_t a = L'ä';
if (a == L'ä') {
std::cout << "if triggered";
}
and if I put the wstring that was loaded from the file, in the file I get the text back. Nothing weird happens there.

Answer 1

This depends on the kind of file encoding.
I would implicitly say that, in this case, UTF-8.
The code below may be work fine:
std::string str;
{
std::ifstream file;
file.open("D:/test.txt");
file >> str;
}
wstring_convert<std::codecvt_utf8<wchar_t>> myconv;
wstring wstr = myconv.from_bytes(str);
size_t l = wstr.length();
for (int i = 0; i < l; i++)
{
auto a = wstr[i];
if (a == L'ä') {
std::cout << "if triggered.";
}
}
However, std::codecvt_utf8 is deprecated in C++17
For the cases using higher C++17:
By MSVC++
I recommend using CString, it's too easy and worked on every almost version of C++, follow this:
std::string str;
{
std::ifstream file;
file.open("D:/test.txt");
file >> str;
}
CString wstr = (CString)CA2W(str.c_str(), CP_UTF8);
size_t l = wstr.GetLength();
for (int i = 0; i < l; i++)
{
auto a = wstr[i];
if (a == L'ä') {
std::cout << "if triggered.";
}
}
#include <atlstr.h> for non-MFC