error C2039: 'string_view': is not a member of 'std'

Question

I have installed a fresh VS2022 (community). I created a MFC app, and I compiled and worked fine. I put the following line of code, in a header, lets say class CMFCApplication1Doc : public CDocument:

// MFCApplication1Doc.h : interface of the CMFCApplication1Doc class
//
#pragma once
constexpr std::string_view whitespaces{ " \t\n\r" };

And from that point, I got:

error C2039: 'string_view': is not a member of 'std'

Of course, I setup c++ 20 standard:

What I am missing here?

Answer 1

Hi, @Flaviu_

From the doc: https://learn.microsoft.com/en-us/cpp/standard-library/string-view?view=msvc-170
Requirements

Header: <string_view>

Namespace: std

• Compiler Option: std:c++17 or later.

You can also use header files that include xstring, such as iostream, string.

string_view header

#ifndef _STRING_VIEW_
#define _STRING_VIEW_
#include <yvals.h>
#if _STL_COMPILER_PREPROCESSOR
#if !_HAS_CXX17
_EMIT_STL_WARNING(STL4038, "The contents of <string_view> are available only with C++17 or later.");
#else // ^^^ !_HAS_CXX17 / _HAS_CXX17 vvv
#include <xstring>
#endif // ^^^ _HAS_CXX17 ^^^
#endif // _STL_COMPILER_PREPROCESSOR
#endif // _STRING_VIEW_

Best regards,

Minxin Yu

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