String and std::string

[Morrison, John]

Robert Collins wrote:
> On Fri, 2003-03-21 at 23:12, Alex Tibbles wrote:
>> <snip>
>> 
>>> I don't care whether you use std::string, or
>>> String++ for any new code,
>>> as long as:
>>> 1) You don't leak memory (std::string will leak if
>>> you use c_str())
>>> IIRC.
>> 
>> I've been unable to confirm this. I tried the attached
>> program (compiled with gcc -lstdc++ stringleak.cpp)
>> and got the following results from top:
> 
> Well, your test is flawed for the behaviour I was referring to. A new
> one is below. 
> 
>> PID USER     PRI  NI  SIZE  RSS SHARE STAT %CPU %MEM
>>   648 alex      14   0   556  556   416 R    56.2  0.2
>> 
>> 
>> TIME COMMAND
>> 3:02 a.out
>> 
>> Am I correct in concluding that std::string::c_str()
>> does not leak? I'm interested as I use c_str() a fair
>> amount for interfacing C++ with C (I believe that was
>> what it was designed for, but I'm only guessing).
>> 
>> 
> ______________________________________________________________________
>> 
>> #include <string>
>> #include <iostream>
>> 
>> int main()
>> {
>> 	std::string bleg("bleg");
>> 	while (true)
>> 	{
>> 		std::cout << bleg.c_str();
>> 	}
>> 
>> 	return 0;
>> }
> 
> the above won't leak, because c_str() returns the internal buffer -
> which isn't being altered. 
> 
> this may well. Look in the g++ library for freeze() (again, IIRC). The
> thing I saw when I was reading the source, was that the internal
> buffer was not delete[]'d once it was handed out via c_str(). That
> was with the libstc++ for gcc 2.95 as well. I've just checked the g++
> 3 implementation, and it's different to what I recall from before...
> 
> 
> #include <string>
> #include <iostream>
> 
> int main ()
> {
> while (true)
>  {
>    std::string foo("bar");
>    foo.append("asdf");
>    char const *leakingpointer = foo.c_str();
>   }
>  return 0;
> }

I thought you were supposed to call release() on any c_str() calls...
of cause, it's been two or three years since I played with this so,
I might be mistaken...

J.


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