Why Does My Code Throw \'no default constructor exists for class \'Blowfish\' \'?

Default Constructor Missing for "Blowfish" Class: Understanding the Error

The error "no default constructor exists for class "Blowfish"" arises when trying to create an instance of the Blowfish class without providing any arguments, despite having defined a constructor that requires a BlowfishAlgorithm argument.

Reasoning for the Error

By default, when a class lacks a constructor, the compiler generates a default constructor that takes no arguments. However, when a non-default constructor is defined (i.e., one requiring arguments), the compiler assumes that constructor handling is explicitly handled by the developer and no longer automatically generates a default constructor. Therefore, providing arguments when creating an instance of the class becomes mandatory.

Solutions

To resolve this error, you have several options:

• Add a Default Constructor: Define a default constructor for the Blowfish class that takes no arguments. For example:

Blowfish() = default;

• Supply Argument to Constructor: When creating an instance of the Blowfish class, explicitly provide the required argument. For instance:

Blowfish blowfish(BlowfishAlgorithm::CBC);

• Use the Designated Initialization Syntax (C 11 or later): Use a constructor that takes an argument and add a = default clause to generate a default constructor. This allows both constructor overloads to coexist.

class GameCryptography {
public:
    GameCryptography(BlofishAlgorithm); // Constructor with argument

    // Generate a default constructor by delegating to the compiler
    GameCryptography() = default;
};

Additional Notes

It's worth highlighting that ECB, CBC, CFB, etc., represent modes of operation for encryption algorithms rather than encryption algorithms themselves. While it doesn't affect compilation, this semantic error can be confusing for code readers.

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