About Pointers Again :(

Question

I am trying to make a pointer that is affected by const. I mean the value that is pointed by pointer cannot change.
char* const ptr="bla bla";
*ptr="hahaha";
And I am trying to change the value of bla bla with the help of pointer. But I am getting an error called "invalid conversion from 'const char*' to char. Can you help me?

Answer 1

`const` means that you can't change the variable's contents! So you by definition can't. Your compiler will even try and optimize away `ptr` entirely if it can and there will be nothing for you to try and change.

Now, you *can* change a variable `x` from `const char*` to `char*`, like this:

const_cast<char*>(x)

But this is only safe if `x` used to be non-const, you made it const later, and now you want to un-const it again.

If you make your string non-const, then you can change it.

char* ptr = "bla bla";

(Or use std::string instead.)

Answer 2

But when I looked to a programming book , I saw that when you use "const" before char, it means you cannot change the data of char. I mean the pointer itself can be reassigned. But we cannot modify the data pointed to by pointer. For example:
const char* ptr;
ptr="hahaha";
ptr="bla bla";//true
*ptr="hahaha";//false
And if we put const after char, it means you can change the data being pointed to. For example:
char* const ptr2="example";
ptr2="error";//false
*ptr2="normal";//it must be true. But I am getting errors. I think my process is true. But changing the value of "example" needs much more effort.

Answer 3

Showing an example can be much more clear. By the way, thank you. @kurvius

Answer 4

Up