Re: C programmer migrating to C++
Bartosz Wiklak wrote:
Hello, I'm coding in C form many years but for a year or something
like that I'm trying to get rig of "bad" old habits and start to do
things better.
There are couple of annoyances in C++ I cannot solve - probably I'm
doing something wrong.
I wonder If someone could help me:
1)
Consider such function definition
void f( int k, const T* t, T2* t2=NULL);
In C I used pointers extensively. When I didn't want to overload
function's definition I used function's default NULL arguments to
indicate that this argument (and part of function's job) is not
relevant. I know this could be considered unsafe but imagine several
function calls inside of such function that also use NULL pointer. It
saves much work. In STL there are some values that represent bad or
boundary values such as string::npos or the one returned by iterator
end() method ( btw, it's irritating that every container has different
past-the-end element). Can I achieve something like default NULL
argument in C++ not using pointers but references?
No you can not use references since a reference must be bound to something.
There is nothing wrong with passing pointers, which can be 0, as
optional parameters. Using 0 instead of 'NULL' in current C++ is better.
In the next version of C++ you can use 'nullptr' instead for better clarity.
2)
Returning objects:
Suppose I want to have a method that returns a "large" object, let it
be a "comp.lang.c++.moderated" string.
I can do it this way:
string& foo( string& buf ){ buf="comp.lang.c++.moderated"; return
buf; }
but I need do such things in my code:
string s;
foo(s);
I would like to do sth. like this:
string s = foo();
If I define foo function like that:
string foo(){ string buf="comp.lang.c++.moderated"; return buf; }
I'll work but as far as I understand it'll run several constructors
and copy constructors and I would like to make such operation work as
fast as [ string s("comp.lang.c++.moderated"); ]
Some gentle advice is to pay less attention to speed and more attention
to design when using C++. There is nothing wrong with your 'string
foo()" function and worrying about its speed is mostly wasting your time.
If an object is very large ( std::string is not ) you might consider
passing back a pointer to such an object. For dynamically allocated
pointers I would suggest you use either std::auto_ptr or
boost::shared_ptr, with the latter being generally much better IMO, and
forego using raw pointers.
BTW, is [ string s("comp.lang.c++.moderated"); ] faster than [ string
s ="comp.lang.c++.moderated"; ] or maybe it is compiler dependent?
It is the exact same thing. They both invoke the constructor.
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