"Expression must have class type" using undocumented library function

Question

I'm having this error trying to understand how to implement this constructor.

I stripped the call out of the function I did have it in, and reached a pretty minimal demonstration of my issue:

uint32_t p=0, c;
uint8_t k=0x00;
c = p.AES::AES(AES_128, k);

I expect the plaintext p to be encrypted by AES with key k to ciphertext c.

Instead, I get the error Expression must have class type, due to my inexperience with OOP no doubt.

Unfortunately the library is not well documented at all, so I cannot even learn by example (without the help of SO!) - what have I done wrong here?

score 5 · Accepted Answer · edited May 23 '17 at 10:26

5

You have multiple problems: First that you use p as an object, but it's a variable of a primitive type. Secondly, you try to call the constructor as a static method.

You should do e.g.

AES c(AES::AES_128, k);

That declares c as a variable of type AES, and you can use the member functions in the class like

c.encryptBlock(someArray, someOtherArray);

It seems to me that you need to learn some basic (and I mean really basic) C++. I suggest you check out The Definitive C++ Book Guide and List.

edited May 23 '17 at 10:26

Community

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answered Jun 30 '14 at 23:33

Some programmer dude

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Thank you - and you're certainly right on the last point. I have Savitch, but haven't read the chapters on (or used C++ for) OOP yet. – OJFord Jun 30 '14 at 23:38

score 1 · Answer 2 · answered Jun 30 '14 at 23:29

You need to scope the enum

AES crypt = AES(AES_TYPE::AES_128, k);

Also to encrypt/decrypt you need to use the following functions, respectively.

void AES::encryptBlock(uint8_t *out, uint8_t *in);
void AES::decryptBlock(uint8_t *out, uint8_t *in);

So you would call it from your crypt object, for example

crypt.encryptBlock();

"Expression must have class type" using undocumented library function

2 Answers2