CODEWITHSUNDEEP
c++constructor
user5626842
user5626842

Reputation:

C++ Cannot call constructor directly in small example

I was wondering, why I cannot call a constructor. Even this small example fails to compile with the message: 

Klassentest.cpp:24:27: error: cannot call constructor 'Sampleclass::Sampleclass' directly [-fpermissive]

Code:

#include <iostream>
using namespace std;

class Sampleclass
{
   public:
    Sampleclass();
};

Sampleclass::Sampleclass(){

}

int main() {
    cout << "!!!Hello World!!!" << endl; // prints !!!Hello World!!!
    Sampleclass::Sampleclass() *qs = new Sampleclass::Sampleclass();
    return 0;
}

I used the Cygwin g++ compiler in version 4.9.3-1.

Thank you for your help.

Upvotes: 9

Views: 29235

Answers (5)

a1o
a1o

Reputation: 1

All answers containing new are bad style in modern c++. In a similar small example, the following worked for me (in C17):

Sampleclass sc = Sampleclass();

Upvotes: 0

M Waseem Shahid
M Waseem Shahid

Reputation: 1

Remove resolution operator, I have an issue that Person::Person() in child class and an error [Error] cannot call constructor 'Student::Person' directly [-fpermissive] but after remove resolution operator solve this error

Upvotes: -1

songyuanyao
songyuanyao

Reputation: 172924

Yes, you can't call ctor directly.

From the standard, class.ctor/2

Because constructors do not have names, they are never found during name lookup;

You might want

Sampleclass *qs = new Sampleclass;

Then the ctor will be called.

Upvotes: 6

cadaniluk
cadaniluk

Reputation: 15229

Sampleclass::Sampleclass() *qs = new Sampleclass::Sampleclass();

is wrong. Sampleclass is a type while Sampleclass::Sampleclass is a constructor. Since the correct syntax is

type identifier = new type();

you need to specify the type here.

Therefore, use

Sampleclass *qs = new Sampleclass();

instead.

Notes:

  • If you didn't know: since C++11 you can simply do

    Sampleclass() = default;

    in the class definition and the default constructor will be defined.

Upvotes: 9

Mike P
Mike P

Reputation: 752

#include <iostream>
using namespace std;

class Sampleclass
{
public:
    Sampleclass();
};

Sampleclass::Sampleclass(){

}

int main() {
    cout << "!!!Hello World!!!" << endl; // prints !!!Hello World!!!
    Sampleclass *qs = new Sampleclass::Sampleclass();
    return 0;
}

You tried to reference the constructor as a type when instantiating your class.

Upvotes: 1

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