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

Flaviu_ 971 Reputation points
2024-06-24T13:36:57.3133333+00:00

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:

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What I am missing here?

C++
C++
A high-level, general-purpose programming language, created as an extension of the C programming language, that has object-oriented, generic, and functional features in addition to facilities for low-level memory manipulation.
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Accepted answer
  1. Minxin Yu 10,791 Reputation points Microsoft Vendor
    2024-06-25T01:26:14.2066667+00:00

    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

    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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