convert int to char

[Dan Feerst]

Should this work?

unsigned long long int msglength;
char message_length[8] = {'(char)msglength'}

They have the same amount of bits. It compiles, but I don't think I'm getting the results I expected. Here is what I'm trying to do.

I'm trying to teach myself bit manipulation. To do this I am trying to write my own SHA-256 algorithm using criteria in FIPS PUB 180-4.

I'm getting stuck at the beginning with the padding. The padding needs to be a multiple of 512 bits. The format is like this

< x input bits >1< y zero bits >< 64 bits denoting the length of x >

It seems that the most logical container for this is a character array.
The part that stumps me the most is the last 64 bits. I thought I came up with an easy way to do it, but I don't think it works. Since I basically just need a 64 bit number, my idea was this. why can't I just store the length in an unsigned long long int and copy it to the last 8 bytes of the padding.
The reason I don't think it works, well this is what I tried.

unsigned long long int msglength = 5;
char message_length[8] = {'(char)msglength'}
cout << message_length[7] <<endl;

since 5 only requires 8 bits I expected that container to be holding the value of 5, or "00000101", I would think the others would be all zero. Instead It prints nothing to the screen. Could someone tell me the error of my ways :)

[iQChange]

Try using reinterpret_cast. http://www.cplusplus.com/doc/tutorial/typecasting/

Bye!

[MatthewRock]

'(char)msglength' should cause an error; "" is used for strings, '' - for single characters.

If you use reinterpret_cast, you will have character for whatever your int in (probably)ASCII is.

If you want to convert number to string, try using stringstream.

[iQChange]

Good one, MatthewRock, but I've thinked on this.
std::stringstream returns an char*, but he's using an char array. Here is the problem. None type-casting can solve it, but I was thinking and... I made it!! std::to_string will make this for you. You can use an std::string. It looks like an "infinite char array". Both need #include <string>

Good Bye!

[Dan Feerst]

thank you both for your help. I'l give that a try.