no default constructor exists for class

Question

include  Includes h    enum BlowfishAlgorithm               ECB          CBC          CFB64          OFB64          class Blowfish   public      struct bf key st               unsigned long P 18           unsigned long S 1024              Blowfish BlowfishAlgorithm algorithm       void Dispose        void SetKey unsigned char data         unsigned char Encrypt unsigned char buffer         unsigned char Decrypt unsigned char buffer         char EncryptIV        char DecryptIV    private      BlowfishAlgorithm  algorithm      unsigned char  encryptIv 200       unsigned char  decryptIv 200       int  encryptNum      int  decryptNum      class GameCryptography   public      Blowfish  blowfish      GameCryptography unsigned char key         void Decrypt unsigned char packet         void Encrypt unsigned char packet         Blowfish Blowfish      void SetKey unsigned char k         void SetIvs unsigned char i1   unsigned char i2            GameCryptography  GameCryptography unsigned char key          Error IntelliSense  no default constructor exists for class  Blowfish

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Because you have this   Blowfish BlowfishAlgorithm algorithm     It s not a default constructor  The default constructor is one which takes no parameters  i e   Blowfish

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If you define a class without any constructor  the compiler will synthesize a constructor for you  and that will be a default constructor -- i e   one that doesn t require any arguments   If  however  you do define a constructor   even if it does take one or more arguments  the compiler will not synthesize a constructor for you -- at that point  you ve taken responsibility for constructing objects of that class  so the compiler  steps back   so to speak  and leaves that job to you   You have two choices  You need to either provide a default constructor  or you need to supply the correct parameter when you define an object  For example  you could change your constructor to look something like   Blowfish BlowfishAlgorithm algorithm   CBC        so the ctor could be invoked without  explicitly  specifying an algorithm  in which case it would use CBC as the algorithm    The other alternative would be to explicitly specify the algorithm when you define a Blowfish object   class GameCryptography        Blowfish blowfish   public      GameCryptography     blowfish  ECB                     In C   11  or later  you have one more option available  You can define your constructor that takes an argument  but then tell the compiler to generate the constructor it would have if you didn t define one   class GameCryptography    public          define our ctor that takes an argument     GameCryptography BlofishAlgorithm            Tell the compiler to do what it would have if we didn t define a ctor      GameCryptography     default       As a final note  I think it s worth mentioning that ECB  CBC  CFB  etc   are modes of operation  not really encryption algorithms themselves  Calling them algorithms won t bother the compiler  but is unreasonably likely to cause a problem for others reading the code

User · Answer

You declared the constructor blowfish as this   Blowfish BlowfishAlgorithm algorithm     So this line cannot exist  without further initialization later    Blowfish  blowfish    since you passed no parameter  It does not understand how to handle a parameter-less declaration of object  BlowFish  - you need to create another constructor for that

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A default constructor is a constructor that either has no parameters  or if it has parameters  all the parameters have default values

[c++] no default constructor exists for class

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