CODEWITHSUNDEEP
c++pointers
bassel27
bassel27

Reputation: 31

How to store the address that a pointer points to to another pointer?

This code aims to make pointer c points to the address that pointer a points to. I can't understand this expression: " char* c= (char*)&a ". Can someone please clarify it?

string* a =new string;
std::cin >> *a;
char* c= (char*)&a;
delete a;

Upvotes: 0

Views: 902

Answers (1)

eerorika
eerorika

Reputation: 238351

How to store the address that a pointer points to to another pointer?

You can copy it:

T* a = some_address;
T* b = a; // copied the address from a to b

I can't understand this expression: char* c= (char*)&a

This declares a variable of type char* which is a pointer to char. The name of the variable is c. The variable is initialised with the expression (char*)&a.

The unary & is the addressof operator. When applied to an lvalue, it results in the address of the object named by the lvalue. In this case, you get the address of the variable a. Note that the address of the variable a is not the same as the address of dynamic object that a points to. Since the type of a is string*, the type of the pointer to a is string**.

(char*)a is an explicit conversion (aka C-style cast). In this case it performs a reinterpret cast from string** to char*. Without context, this conversion seems to make no sense, but it makes the example well-formed regardless. Don't use C-style casts in C++.

P.S. Avoid unnecessary dynamic allocation. If string is std::string, then there is hardly ever a reason to allocate it dynamically.

I'm trying to make c point to the memory address of the first letter in string *a. How do I do that?

There are no letters in a at all. a simply contains the address of a string object.

If you want to point to the first character that is stored in the buffer managed by the string that is pointed by a - with the assumption that string is std::string, then you can indirect through a and use the data member function of std::string:

char* c = a->data();

Upvotes: 2

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