Why Does Instantiating a Blowfish Object Without Arguments Produce a \'no default constructor\' Error, and How Can This Be Fixed?

Error: "no default constructor exists for class "Blowfish""

Question:

When attempting to instantiate an object of the Blowfish class without explicitly specifying a constructor argument, the compiler emits the error message, "no default constructor exists for class "Blowfish"." Why is this occurring, and how can it be resolved?

Answer:

The absence of a default constructor in the Blowfish class is by design. When a class defines even a single constructor, the compiler no longer synthesizes a default constructor by default.

Solutions:

To resolve this error, you have the following options:

1. Provide a default constructor: Define a default constructor that does not require any arguments. For example:

Blowfish() : _algorithm(CBC) {}

2. Specify an argument when instantiating the object: Explicitly specify the desired BlowfishAlgorithm value when creating an object of the Blowfish class. For example:

Blowfish blowfish(ECB);

3. Use C 11's = default: Define a constructor that takes an argument, but also instruct the compiler to generate the constructor it would have created if you hadn't defined one. This is done with the = default syntax. For example:

class GameCryptography {
public:
    GameCryptography(BlofishAlgorithm);

    // Generate the default constructor
    GameCryptography() = default;
};

Additional Notes:

Note that the terms "ECB," "CBC," "CFB," etc., are modes of operation for encryption algorithms rather than encryption algorithms themselves. Using these terms as algorithm names could potentially lead to misunderstandings and errors.

The above is the detailed content of Why Does Instantiating a Blowfish Object Without Arguments Produce a \'no default constructor\' Error, and How Can This Be Fixed?. For more information, please follow other related articles on the PHP Chinese website!