CODEWITHSUNDEEP
c++c++11c++17
ge45mue
ge45mue

Reputation: 707

Avoid calling move constructor

I have following example 

#include <cstdint>

class FooC
{
public:
   FooC(uint16_t iPort, uint16_t iPin)
   : PORT(iPort)
   , PIN(iPin)
   {
   };

   ~FooC() = default;

   FooC() = delete;
   FooC(const FooC&) = delete;
   FooC(FooC&&) = delete;

private:
   const uint16_t PORT;
   const uint16_t PIN;
};

int main()
{
    FooC array[2] = {
       FooC(1,2),
       FooC(3,4)
    };
}

and I don't want to call the default, move and copy constructor. Due to that I deleted the functions. Unfortunately this results in following error (compiled with C++11)

: In function 'int main()':

:28:5: error: use of deleted function 'FooC::FooC(FooC&&)'

 };

 ^

:16:4: note: declared here

FooC(FooC&&) = delete;

^~~~

:28:5: error: use of deleted function 'FooC::FooC(FooC&&)'

 };

 ^

:16:4: note: declared here

FooC(FooC&&) = delete;

^~~~

Compiler returned: 1

Is it possible to force in this example the calling of constructor with the parameters and still delete the default, move and copy constructor?

Upvotes: 14

Views: 719

Answers (3)

rad123
rad123

Reputation: 187

No, not possible.

What you can do is don't mention these lines :

FooC() = delete;
FooC(const FooC&) = delete;
FooC(FooC&&) = delete;

So, now your code only will have default destructor. The compiler will not generate any move constructor or move assignment operator as destructor is defined(default). This is surpass your error, and

Upvotes: 0

NathanOliver
NathanOliver

Reputation: 180835

Is it possible to force in this example the calling of constructor with the parameters and still delete the default, move and copy constructor?

No with your current syntax (before C++17) and yes (in C++17).

Pre-C++17:

This is not possible. The aggregate initialization copies the initializers into the aggregate. This means you have to have an accessible copy/move constructor. In C++11 you have to pass the constructor parameters as their own braced-init-list. This means you aren't copying FooC's but instead copy-list-initializing the FooC's in the array which calls the 2 parameter constructor instead of the copy/move constructor.

FooC array[2] = {
   {1, 2},
   {3, 4}
};

C++17:

You no longer have temporary objects in the braced-init-list and each element of the array will be directly initialized instead of copy initialized.

Upvotes: 5

Kerrek SB
Kerrek SB

Reputation: 477308

In C++11 and C++14, you can use nested braces:

FooC array[2] = {{1,2}, {3,4}};

In C++17 your code should already work as written thanks to the new prvalue/materialization rules ("guaranteed copy elision").

Upvotes: 14

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