Don't understand errors on HelloWorld in VS when included std_lib from Stroustrup's book [duplicate]

Question

I included std_lib from Stroustrup's web-site My code is:

#include "c:\Users\theresmineusername\Documents\Visual Studio 2017\std_lib_facilities.h"

int main()
{
    cout << "Hello, World!\n";
    return 0;
}

So I got 2 errors:

1. E1574    статическое объявление не удалось по причине "<hash_map> is deprecated and will be REMOVED. Please use <unordered_map>. You can define _SILENCE_STDEXT_HASH_DEPRECATION_WARNINGS to acknowledge that you have received this warning."   ConsoleApplication2 c:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Tools\MSVC\14.10.24930\include\hash_map

2. C2338    <hash_map> is deprecated and will be REMOVED. Please use <unordered_map>. You can define _SILENCE_STDEXT_HASH_DEPRECATION_WARNINGS to acknowledge that you have received this warning.  ConsoleApplication2 c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.10.24930\include\hash_map

From the beginning of book there using "std_lib_facilities.h" and in everything but pathway of this std_lib my code is equivalent to the book. Can someone explain what it mean? Can's go next through the book with it.

Answer 1

std_lib_facilities.h is a header file written by Stroustrup himself which can be downloaded from www.stroustrup.com. It is not a standard C++ header but apparently reflects Stroustrup's idea of hiding even the simplest complexities of the language from total beginners in their first few weeks.

As the header file itself says:

This header is primarily used so that you don't have to understand every concept all at once.

I personally think that this is a very bad idea, with all due respect for Bjarne Stroustrup who is a greater genius than I could ever aspire to be.

The header file is full of things considered bad programming style (especially using namespace std;, which should never be used at global scope in a header file, or deriving from standard container classes). It also caters to outdated compilers which may not yet support certain "newer" features of C++ correctly, using a lot of ugly preprocessor directives.

It seems that the header file itself is quite outdated already (the one I linked to is 7 years old), and I'm not sure if Stroustrup ever updated it.

One of the preprocessor directives makes your compiler incorrectly include <hash_map>, when it should be <unordered_map>. Of course, that's absurd, because your program just wants to print a hello world message and is not even interested in hash maps.

Here's how your program should look like in correct C++:

#include <iostream>

int main()
{
    std::cout << "Hello, World!\n";
    return 0;
}

(Note that the return 0; is optional in main.)

If, however, you want to keep going with the std_lib_facilities.h learning aid provided by Stroustrup which you have to unlearn in a few weeks anyway, then do what the error message itself says: define _SILENCE_STDEXT_HASH_DEPRECATION_WARNINGS.

The quickest way to do so is with a #define in the source code:

#define _SILENCE_STDEXT_HASH_DEPRECATION_WARNINGS
#include "c:\Users\theresmineusername\Documents\Visual Studio 2017\std_lib_facilities.h"

int main()
{
    cout << "Hello, World!\n";
    return 0;
}

When the times comes, throw it away together with the #include for std_lib_facilities.h.

Answer 2

The idiomatic way to write this in c++ is:

#include <iostream>

int main() {
    std::cout << "Hello World!\n";
}

The header file from the book examples shouldn't be used.