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?

Thank you!

CodePudding user response：

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.

CodePudding user response：

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.