YemSalat:
I would still like to be able to save user the hassle of having to calculate sizes when the new string must contain both substrings completely.
Regarding the same problems as the original String class - I do want to avoid that kind of stuff, but everywhere I read it seems likesnprintfis a really safe option.
I have not studied the code behind the String class but my understanding is that there are, potentially, two types of problem. One is that it frequently creates new copies of a string while it is doing its work and can therefore use up a lot of memory that the user cannot be aware of. The other is that it may not release all the unused memory in an adequate fashion.
My strong sense is that what you say in the first sentence I have quoted will have a similar effect of consuming memory that the user has not allocated, or made allowance for in his/her program design. It matters little that it might be a tidier user of memory than the String class - that just postpones the crash.
I also think it is psychologically a good thing to force users to be aware of the memory limitations rather than hide it all from them. Hiding the C functions such as strcpy() will be sufficient.
...R