[Boost-users] Re: Concatenation of many std::string

From: Yuval Ronen (ronen_yuval_at_[hidden])
Date: 2005-02-11 04:56:43

>>I've then worked on a method, just by adding a special object after the '='
>>sign, which transforms these concatenations into a two pass operation, the
>>first to calculate the total length and allocate the destination string, and
>>the second pass to actually copy the source strings into the destination.
>>
>>One just need to re-write the concatenations this way :
>>std::string a = my_special_object() + b + c + d + e ;
>>
>>But maybe I am reinventing the wheel. Is there in Boost, a way to speed up
>>this kind of operation ?
> 
> 
> I'm not aware of anything in boost - the string algo lib seemed like a
> natural place but I didn't see anything.
> 
> I wrote something like that.  I'm not sure if it's really safe and
> correct and all - I believe the temporary lifetime relied on is
> guaranteed ....
> 
> You can write:
> 
> std::string s1;
> s1 << concat () + a + b + c;
> 
> or 
> 
> std::string s2 = concat () + a + b + c;

Hmmm, this sounds interesting to me. I have to admit that's an idea I've 
never thought of before. Am I right to assume that the temporary concat 
object holds some kind of a container-of-pointers to the concatenated 
strings? And this container will be pushed_back with every operator+? 
And finally, assignment of this to string will only then calulate the 
resulted string? I guess the trick is how to avoid memory alllocation 
while push_backing. One can use a regular by-value fixed-size c-array of 
pointers as a concat class member, but that complicates the code on 
what-to-do-when-it's-full. Any other ideas?

Just a few thoughts...
Yuval