simple question about pointers and casting

Hello,

I am just experimenting with some code. And I am not sure why I need to cast to an unsigned char*.

I get this error: cannot convert from 'unsigned char' to 'unsigned char *'
I can understand that the pointer is an unsigned char. But if I am assigning the address of the myFloat which I am casting a unsigned char. Why do I need to cast it as a pointer as well?

Code:

float myFloat = 10000;
unsigned char *ptrChar;
ptrChar = (unsigned char *) &myFloat;

//Why can't I just do this?
ptrChar = (unsigned char) &myFloat;

The following example using a int:

Code:

int myInt = 1000;
int *ptrInt = &myInt;

As the pointer is an int and I am assigning the address of myInt this works perfectly ok.

However, with the example above I have converted to a unsigned char.

Many thanks for clearing this up.

Steve

It's because "unsigned char" is a different type from "unsigned char *". Observe.

Code:

char c;
char *p = &c;
unsigned char uc = (unsigned char)c;
unsigned char *up = (unsigned char *)p;

An unsigned char is (usually) one byte. It usually stores a value from 0 to 255.
A unsigned char * is usually four or eight bytes. It stores the address of another variable, the address of an unsigned char somewhere else in memory.

So unsigned char and unsigned char * are completely different types. You have to tell the compiler which of them you want to use. Both can be used, but both give you very different values.

Code:

unsigned char c = 'a';
unsigned char *anotherp = (unsigned char *)c;
unsigned char anotherc = (unsigned char)c;

The value of anotherp is dubious, but it can be done if you really want to.

Rationale: when specifying types, use the name of the type (like "unsigned char"), as well as any levels of indirection (with asterisks).

Incidentally, casting a float * to an unsigned char * isn't usually much use unless you are trying to examine each byte of the float individually or something.

Also, if you're using C++ you shouldn't use C style casts. C++ has 4 safer casts:
static_cast
dynamic_cast
const_cast
reinterpret_cast

In this case you'd probably use static_cast<>. Assuming you're using C++, of course.