Re: std:string assignments
"Erik" <eriks@dsv.su.se> wrote in message
news:fan6729b7el85987t2at3r8tmnjre8qc69@4ax.com...
Hello,
For many years ago I implemented my own string buffer class, which
works fine except assignments - it copies the char* buffer instead of
the pointer. Therefore in function calls I pass "const char*" and get
the result in a parameter by reference "MyString& result".
I'd like to move to nicer strings. In order to keep platform/compiler
independence I consider std:string as the replacement. While googling
I managed to read some warnings about std:string not being thread safe
(any shared memory is not without a lock, is it?).
Correct, if you want to make it thread safe you will need to wrap it in a
thread safe class with your own locking mechanisms. On a side note, if you
do this you probably won't have to write locking for every string function,
only the ones you'll be using, although that can be a bit.
I wonder about
assignment - does it copy the buffer or the pointer?
Buffer.
I managed to find
only one document which explicitly warned about
"implementation-specific issues" where any reference to the memory
makes the buffer unique.
I'm not sure what you mean here, are you talking about .c_str()? And yes,
the memory .c_str() points too only remains until the string has changed.
I'm not sure if it becomes invalidated at that point or not. It's best to
only use .c_str() for short lived operations (copy it to a buffer, output
it, etc...)
Any other problems on moderns compilers?
It depends on what you consider a problem I guess.
I checked the following assignment on Borland C++ Builder:
string s1 = "abc";
string s2 = s1;
cerr << (int)s1.c_str() << ' ' << (int)s2.c_str();
s1.c_str() and s2.c_str() show different addresses. I wonder whether
the assignment or c_str() copied the buffer.
Yes, it would copy the buffer. Two different strings are unique and contain
their own pointer to their own memory for storage of the data. s2 has it's
own data pointer which gets allocated with enough memory to hold the string
"abc" (and maybe some more) then the data gets copied into this buffer.
If I return a string from a function, would it return a pointer or
would copy the buffer (copy constructor).
Usually it would copy the buffer but the compiler may optimize this away if
you're real lucky.
Should I abandon my own string buffer at all knowing it works?
It depends on how different std::string is for you and if you can get it to
work. If it does 90% excactly the same as your string class, I would
probably switch to std::string and deal with the differences. If they are
only 50% compatable I would take a closer look.