Thread: a const question

I am did something like this:

struct myStruct {
File *file
.
.
.
};

status someMethod (const File *file, int a) {

myStruct *struct01 = new myStruct;

.
.
.

struct01->file = file;

.
.
.
}

Can I do something like that? The compiler gave an error if I do this. I tried with:

struct01->file = (File*)file;

and it works. Do I have to cast it to make it work?

Thanks

This is a really tricky and subtle problem involving the const qualifier. Put simply, in the context of pointers, you can't assign a const pointer to a non const pointer without a cast but you can assign a non const pointer to a const pointer. The C++ standard explains it in the usual cryptic way, but this is pretty much what it boils down to.

Yes, but cast like this:

Code:

struct01->file = const_cast<File*>(file);

Yes, but cast like this:


code:--------------------------------------------------------------------------------
struct01->file = const_cast<File*>(file);
--------------------------------------------------------------------------------

Hmm..what does const_cast do?

Is it specifically only for casting const data?

C/C++ is a case sensitive language...try this (I haven't tested it, but it has a good chance...)

Code:

struct myStruct {
FILE *file
.
.
.
};

status someMethod (const FILE *file, int a) {

myStruct *struct01 = new myStruct;

.
.
.

struct01->file = file;

.
.
.
}

C/C++ is a case sensitive language...try this (I haven't tested it, but it has a good chance...)

Oops, I did made a mistake when posting the code to the forum, but I did used FILE in my code.

Originally posted by heljy
Hmm..what does const_cast do?

It is used to remove const or mutable specifiers from a type:

Code:

const int* a = 3;

int* b = a; //Error
int* c  = const_cast<int*>(a); //OK

const int* a = 3;

int* b = a; //Error
int* c = const_cast<int*>(a); //OK

That makes sense

Ur previous

int* c = const_cast<int>(a); //OK

had me confused for a while

"edit post" is a great feature.