Re: [PATCH 5/7] xml-support.c: Use std::string for growing string buffer

[Simon Marchi <simon dot marchi at polymtl dot ca>]

On 2017-04-15 00:36, Simon Marchi wrote:
> On 2017-04-10 08:22, Pedro Alves wrote:
> > This main idea behind this patch is this change to 
> > xml-support.c:scope_level
> >
> >   -  /* Body text accumulation.  This is an owning pointer.  */
> >   -  struct obstack *body;
> >   +  /* Body text accumulation.  */
> >   +  std::string body;
> >
> > ... which allows simplifying other parts of the code.
> >
> > In target_fetch_description_xml, we want to distinguish between
> > returning "success + empty std::string" and "no success", and
> > gdb::optional is a natural fit for that.
>
> When growing a string like that, isn't it more efficient to use a 
> stringstream?

Nevermind, I think I got confused with Java, where string objects are 
immutable.  So every time you do an append, it actually allocates a new 
string object.  It's therefore good practice to use a StringBuilder in 
those cases.  The C++ string works similarly to a vector (with 
exponential capacity growth), so the number of reallocations is not bad.

Simon