Question 135905 in Visual Studio Code Question posted in
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Visual Studio Code – Error C2280 in a simple piece of C++ code

I’m trying to solve a "stupid" problem I got with Visual Studio Enterprise 2022.

I created a new MFC application from scratch, then I added this single line of code:

CFile testFile = CFile(_T("TEST STRING"), CFile::modeCreate);

When I try to build the solution, I get this error from the compiler:

error C2280: 'CFile::CFile(const CFile &)': attempting to reference a deleted function

I read lot of answers and also the official MS Guide about this error but I still cannot figure how to solve.

Any hint?

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2

Answers


  1. 0

    CFile objects can’t be copied, but that is exactly what you are trying to do – you are creating a temporary CFile object and then copy-constructing your testFile from it. 1

    Use this instead to avoid the copy and just construct testFile directly:

    CFile testFile(_T("TEST STRING"), CFile::Attribute::normal);

    1: I would be very worried by the fact that the compiler is even complaining about this copy, instead of just optimizing the temporary away, as all modern C++ compilers are supposed to do.

    This statement:

    CFile testFile = CFile(_T("TEST STRING"), CFile::Attribute::normal);

    Is effectively just syntax sugar for this (hence the delete‘d copy constructor being called):

    CFile testFile(CFile(_T("TEST STRING"), CFile::Attribute::normal));

    Which modern compilers since C++17 onward are supposed to optimize to this:

    CFile testFile(_T("TEST STRING"), CFile::Attribute::normal);

    However, at least according to MSDN, Visual Studio defaults to C++14 by default. So make sure you are compiling for a later C++ version instead.

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  2. 0

    It seems you are compiling your program using a compiler that does not support C++ 17 or higher.

    Before the C++ 17 Standard if the copy constructor is deleted then such a record

    CFile testFile = CFile(_T("TEST STRING"), CFile::Attribute::normal);

    is incorrect. The compiler will request that the copy constructor will be available.

    Starting from C++ 17 even if the copy constructor is deleted nevertheless this record

    CFile testFile = CFile(_T("TEST STRING"), CFile::Attribute::normal);

    is correct.

    Here is a demonstration program using gcc 12.2

    int main() 
{
    struct A
    {
        A( const char *)
        {
        }
        A( const A & ) = delete;
    };

    A a = A( "Hello C++17!" );
}

    If to compile the program setting the option -std=c++14 then the compiler issues the error

    <source>:207:33: error: use of deleted function 'main()::A::A(const main()::A&)'
  207 |         A a = A( "Hello C++17!" );

    However if to use the option -std=c++17 then the program compiles successfully.

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