C++ : Does char pointer to std::string conversion copy the content?

Question

When I convert a char* to std::string using the constructor:

char *ps = "Hello";
std::string str(ps);

I know that std containers tend to copy values when they are asked to store them. Is the whole string copied or the pointer only? if afterwards I do str = "Bye" will that change ps to be pointing to "Bye"?

they have assignment operators overloaded and actually if i am guessing correctly they would use copy and swap algorithm. and a temporary string object will be created from char*. — Koushik Shetty, May 08 '13 at 11:29
@Koushik: you're guessing wrong. Making a shallow copy here would be counterintuitive and prone to errors. — Violet Giraffe, May 08 '13 at 11:33
@VioletGiraffe yes i realise the pointer is not copied and there is a deep copy and there should be an internal buffer to hold this. — Koushik Shetty, May 08 '13 at 11:36
Don't assign string literals to `char*`, always use `const char*`. String literals are not supposed to change. — Sebastian Redl, May 08 '13 at 12:03

Violet Giraffe · Accepted Answer · 2016-12-26T16:28:06.183

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std::string object will allocate internal buffer and will copy the string pointed to by ps there. Changes to that string will not be reflected to the ps buffer, and vice versa. It's called "deep copy". If only the pointer itself was copied and not the memory contents, it would be called "shallow copy".

To reiterate: std::string performs deep copy in this case.

edited Dec 26 '16 at 16:28

answered May 08 '13 at 11:30

Violet Giraffe

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Can you add a source for that? – Philipp Ludwig Dec 07 '18 at 12:29
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@PhilippLudwig The Standard (N4140, §21.4-2) says *The member functions of `basic_string` use an object of the `Allocator` class passed as a template parameter to allocate and free storage for the contained char-like objects.* – ynn Feb 05 '20 at 14:41

score 5 · Answer 2 · edited Apr 25 '18 at 10:43

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str will contain a copy of ps, changing str will not change ps.

edited Apr 25 '18 at 10:43

Azeem

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answered May 08 '13 at 11:30

parkydr

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C++ : Does char pointer to std::string conversion copy the content?

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