问题
My application is having memory problems, including copying lots of strings about, using the same strings as keys in lots of hashtables, etc. I'm looking for a base class for my strings that makes this very efficient.
I'm hoping for:
- String interning (multiple strings of the same value use the same memory),
- copy-on-write (I think this comes for free in nearly all std::string implementations),
- something with ropes would be a bonus (for O(1)-ish concatenation).
My platform is g++ on Linux (but that is unlikely to matter).
Do you know of such a library?
回答1:
If most of your strings are immutable, the Boost Flyweight library might suit your needs.
It will do the string interning, but I don't believe it does copy-on-write.
回答2:
copy-on-write (I think this comes for free in nearly all std::string implementations)
I don't believe this is the case any longer. Copy-on-write causes problems when you modify the strings through iterators: in particular, this either causes unwanted results (i.e. no copy, and both strings get modified) or an unnecessary overhead (since the iterators cannot be implemented purely in terms of pointers: they need to perform additional checks when being dereferenced).
Additionally, all modern C++ compilers perform NRVO and eliminate the need for copying return value strings in most cases. Since this has been one of the most common cases for copy-on-write semantics, it has been removed due to the aforementioned downsides.
回答3:
Andrei Alexandrescu's 'Policy Based basic_string implementation' may help.
回答4:
Take a look at The Better String Library from legendary Paul Hsieh
来源：https://stackoverflow.com/questions/1116040/memory-efficient-c-strings-interning-ropes-copy-on-write-etc