在未签名和已签名字符之间进行转换。 如何？

Question

I have a question, being a student I have to use OpenSSL. My task is to calculate a RSA signature with blinding, and it uses both char and unsigned char . I said this in case anyone is wondering why I'm using these types, char and unsigned char , so intricately.

My question is what are the rules and good practice advice to using a cast from and to char / unsigned char applied to itself without a pointer, to vector/pointers and, why not, to matrices.

If anymore details are needed I am happy to comply. It goes without saying that I have searched but couldn't find a satisfying answer to anything else than casting int and unsigned int, thus if this is a repost point me in the right direction without hesitation.

Answer 1

char yourChar = 'a';
unsigned char yourUChar = static_cast<unsigned char>(yourChar);

int yourInt = 1;
unsigned int yourUInt = static_cast<unsigned int>(yourInt);

A vector is just multiple ints, you'd cast each member in the vector. Same goes with a matrix.

If you cast a signed value that has a negative value, to an unsigned type, it will likely produce undesired behavior. For example, casting -1 to an unsigned int would give you the bitwise value of -1 cast to an unsigned int. A 32-bit signed int that is -1 is 0xFFFFFFFF in hex, all 1s in binary, and casting that to unsigned would leave the bits as 1s but not you have the largest possible 32-bit unsigned int, which is 4,294,967,295.