String and std::string

[Robert Collins]

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;
}
-- 
GPG key available at: <http://users.bigpond.net.au/robertc/keys.txt>.
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