How to you get the address of an element in an std::string in C++? [duplicate]

Question

For example, i have the following string :

std::string s = "Hello, World!"

I want the address of the last element of s which is '!'.

I tried the following code, but it does not seem to output what I want it to.

std::cout << &s[s.length() - 1];

That outputs '!' not it's address, the same happens with s.back()

Is it because of the formatting caused by std::cout or is the problem elsewhere?

Basically I want a function that outputs the address of the last (and if possible, the first) element in a string.

Remy Lebeau · Accepted Answer · 2017-07-04 16:33:47Z

9

Currently, you're using the overload of operator<< that takes a const char* as input. It treats the input as a null-terminated C string.

If you cast to (const void*) the problem will go away:

std::cout << (const void*)(&s[s.length() - 1]);

edited Jul 4, 2017 at 16:33

Remy Lebeau

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answered Jul 4, 2017 at 16:14

Bathsheba

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3 Comments

Some programmer dude Over a year ago

My only complaint is that you use a C-style cast.. A static_cast should be preferred IMO. :)

Bathsheba Over a year ago

@Someprogrammerdude: I see your point, but I feel that's at the expense of readability at the call site. Perhaps I spent too much time in my youth programming in C ;-)

Hatted Rooster Over a year ago

You're still in your youth!

Curious · Accepted Answer · 2017-07-04 16:14:54Z

1

auto address_back = &s.back();
auto address_front = &s.front();

cout << static_cast<void*>(address_back) << endl;
cout << static_cast<void*>(address_front) << endl;

answered Jul 4, 2017 at 16:14

Curious

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