compiler is complaining for this string hash function I found online:
error: invalid conversion from 'void*' to 'unsigned char*'
Code://FNV string hash fcn (src:http://eternallyconfuzzled.com/tuts/algorithms/jsw_tut_hashing.aspx) unsigned fnv_hash ( void *key, int len )//Q: how do I use generic ptr key? { unsigned char* p = key; unsigned h = 2166136261U; int i; for ( i = 0; i < len; i++ ) h = ( h * 16777619 ) ^ p[i]; return h; }
If you are using a C++ compiler you will probably need to cast your void* to the proper type.
Jim
It's fixed w/ casting as you mentioned:
BUT shouldnt' it just beCode:unsigned char* p = (unsigned char*)key;
which doesn't compile. I ask b/c in function parameters, we have declared key to be a void pointer, so if it's already a pointer, I'd think the (unsigned char*)key would be dereferencing a ptr...Code:unsigned char* p = (unsigned char)key;
Last edited by monkey_c_monkey; 07-11-2012 at 08:07 PM.
we have declared key to be a void pointer, so if it's already a pointer, I'd think the (unsigned char*)key would be dereferencing a ptr[/quote]
The syntax that you're using is:
Hence, there is no dereferencing. You are type casting. Therefore, you should be casting to unsigned char*, not unsigned char.Code:x = (type_of_x)y;
EDIT:
Then again, in this case consider using static_cast, e.g.,
Code:unsigned char* p = static_cast<unsigned char*>(key);
Last edited by laserlight; 07-11-2012 at 08:02 PM.
Look up a C++ Reference and learn How To Ask Questions The Smart WayOriginally Posted by Bjarne Stroustrup (2000-10-14)
I have not learnt about static_cast, but for the type casting format, it's still confusing... But if that's how the compilers roll, I'll go w/ it... I hope you see where my logic is.
But, you know, a cast merely changes the type of something. It never dereferences something.
Therefore, if you do
unsigned char* p = (unsigned char)key;
You are telling the compiler to take the pointer, and convert it (truncate it) to fit an unsigned char. Doesn't make sense.
unsigned char* p = (unsigned char*)key;
This on the other hand tells the compiler to change key into a unsigned char*, which makes sense because we want it to be a pointer to char.
Re not having learned static_cast: google it.
