Does c_str property of string class allocate memory?

[Alfonso Morra]

Hi,

Doest the c_str() method of the string class allocate memory. if it does
alloc mem behind the scenes - whose responsibility is it to cleanup
after (i.e. free the returned char*?)

Tkx

[peter.koch.larsen@gmail.com]

Re: Does c_str property of string class allocate memory?


Alfonso Morra wrote:[color=blue]
> Hi,
>
> Doest the c_str() method of the string class allocate memory. if it does
> alloc mem behind the scenes - whose responsibility is it to cleanup
> after (i.e. free the returned char*?)
>
> Tkx[/color]
This is not specified in the standard, so the answer is "could be", but
I haven't yet met a string which did allocate.
In all cases you are not responsible for the deallocation.

/Peter

[Robbie Hatley]

Re: Does c_str property of string class allocate memory?

"Alfonso Morra" <sweet-science@the-ring.com> wrote in message news:dharad$o8g $1@nwrdmz02.dmz .ncs.ea.ibs-infra.bt.com...[color=blue]
> Hi,
>
> Doest the c_str() method of the string class allocate memory. if it does
> alloc mem behind the scenes - whose responsibility is it to cleanup
> after (i.e. free the returned char*?)
>
> Tkx[/color]

That's up to the compiler author.

You don't need to worry about allocation or deallocation;
that's all handled for you automatically.

Some warnings about c_str() :

If you do something like this:

std::string Catz = "Round and round she goes!";
const char* Batz = Catz.c_str();

Then Batz is a pointer to an object which is owned by the
std::string object Catz. This means you need to remember
these two things:

1. You can NOT write to the location pointed to by Batz!
It's read-only. In fact, a good compiler won't even
let you omit the "const" in the definition of Batz above.

2. If Catz goes out of scope, Batz is no-longer guaranteed
to point to anything useful. Dereferencing Batz at that
point might crash your program (or your system).


Cheers,
Robbie Hatley
Tustin, CA, USA
email: lonewolfintj at pacbell dot net
web: home dot pacbell dot net slant earnur slant

[Alfonso Morra]

Re: Does c_str property of string class allocate memory?



Robbie Hatley wrote:[color=blue]
> "Alfonso Morra" <sweet-science@the-ring.com> wrote in message news:dharad$o8g $1@nwrdmz02.dmz .ncs.ea.ibs-infra.bt.com...
>[color=green]
>>Hi,
>>
>>Doest the c_str() method of the string class allocate memory. if it does
>> alloc mem behind the scenes - whose responsibility is it to cleanup
>>after (i.e. free the returned char*?)
>>
>>Tkx[/color]
>
>
> That's up to the compiler author.
>
> You don't need to worry about allocation or deallocation;
> that's all handled for you automatically.
>
> Some warnings about c_str() :
>
> If you do something like this:
>
> std::string Catz = "Round and round she goes!";
> const char* Batz = Catz.c_str();
>
> Then Batz is a pointer to an object which is owned by the
> std::string object Catz. This means you need to remember
> these two things:
>
> 1. You can NOT write to the location pointed to by Batz!
> It's read-only. In fact, a good compiler won't even
> let you omit the "const" in the definition of Batz above.
>
> 2. If Catz goes out of scope, Batz is no-longer guaranteed
> to point to anything useful. Dereferencing Batz at that
> point might crash your program (or your system).
>
>
> Cheers,
> Robbie Hatley
> Tustin, CA, USA
> email: lonewolfintj at pacbell dot net
> web: home dot pacbell dot net slant earnur slant
>
>[/color]
tkx

[Default User]

Re: Does c_str property of string class allocate memory?

Robbie Hatley wrote:

[color=blue]
> Some warnings about c_str() :
>
> If you do something like this:
>
> std::string Catz = "Round and round she goes!";
> const char* Batz = Catz.c_str();
>
> Then Batz is a pointer to an object which is owned by the
> std::string object Catz. This means you need to remember
> these two things:
>
> 1. You can NOT write to the location pointed to by Batz!
> It's read-only. In fact, a good compiler won't even
> let you omit the "const" in the definition of Batz above.
>
> 2. If Catz goes out of scope, Batz is no-longer guaranteed
> to point to anything useful. Dereferencing Batz at that
> point might crash your program (or your system).[/color]

Worse than that, if there's any call to a non-const member function of
Catz, then Batz is no longer valid. It's a poor idea to EVER try to
keep the pointer returned. You should always get a fresh copy before
using it.




Brian

[Mike Wahler]

Re: Does c_str property of string class allocate memory?


"Alfonso Morra" <sweet-science@the-ring.com> wrote in message
news:dharad$o8g $1@nwrdmz02.dmz .ncs.ea.ibs-infra.bt.com...[color=blue]
> Hi,
>
> Doest the c_str() method of the string class allocate memory.[/color]

Maybe, maybe not.
[color=blue]
> if it does alloc mem behind the scenes - whose responsibility is it to
> cleanup after (i.e. free the returned char*?)[/color]

The std::string class handles all its own memory management,
as do all the other standard library types.

-Mike