Use of undeclared identifier '_O_U16TEXT'

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

int main() {
    _setmode(_fileno(stdout), _O_U16TEXT);
    std::wcout << L"Hello, this is a Unicode text!" << std::endl;
    return 0;
}

1. #include <iostream>: Includes the input/output stream header file for standard input/output operations.
2. #include <fcntl.h>: Includes the file control header file, which contains definitions for file control operations.
3. #include <io.h>: Includes the input/output header file, providing declarations for input/output functions.
4. int main() { ... }: Defines the main function, the entry point of the program.
5. _setmode(_fileno(stdout), _O_U16TEXT);: Sets the output mode to output Unicode text by changing the mode of the standard output stream to _O_U16TEXT.
6. std::wcout << L"Hello, this is a Unicode text!" << std::endl;: Outputs a Unicode string using wide characters to the console.
7. return 0;: Indicates successful termination of the program.