Why Does \'no default constructor exists for class\' Appear in C When Instantiating a Class with an Embedded Class Lacking a Default Constructor?

"no default constructor exists for class" Error in C

When attempting to instantiate an instance of the GameCryptography class without providing a constructor argument, an IntelliSense error message indicating that no default constructor exists for the Blowfish class is encountered.

This error occurs because the GameCryptography constructor attempts to initialize an embedded instance of Blowfish without providing a constructor argument. By default, C synthesizes a constructor for a class without a user-defined one. However, if the class does have a user-defined constructor, the default constructor is not synthesized.

To resolve the error, one of the following strategies can be implemented:

• Provide a Default Constructor: Define a default constructor for the Blowfish class that initializes the algorithm field with a default value, such as:

Blowfish() : _algorithm(CBC) {}

• Supply Constructor Argument: Provide an explicit constructor argument when creating an instance of the Blowfish class, such as:

GameCryptography(unsigned char key[]) : _blowfish(CBC) {}

• Use C 11 Default Constructor: In C 11 or later, use the default keyword to instruct the compiler to generate the default constructor that would have been synthesized automatically if no user-defined constructor existed, such as:

class Blowfish {
public:
    Blowfish(BlowfishAlgorithm algorithm) {}
    Blowfish() = default;
};

• Correct Terminologies: Additionally, consider using the correct terminology. The modes of operation (e.g., ECB, CBC) should be referred to as such, rather than collectively called algorithms.

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