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So I had this at first (and tried stringstream as a class variable) and couldn't figure out why it wasn't working. It either printed out weird characters or nothing (or spaces?).
This is when I checked the discussion and found elvis_dukaj's solution using stringstream inside the constructor and making the string object a class variable.
So, I'm wondering why the cout works but when using return, it doesn't?
Also, I read Pan_Zloto's explanation but still confused. So I guess I'd like a better explanation. Why can't you use a stringstream class variable but a string class variable works?
I didn't really understood this. I don't know much about how the copy constructor works, and when it is deleted. So, looking for some more explanation!
Thanks for the help though!
the copy constructor defines how to copy objects of the class "properly". If undefined than it just duplicates the members of the class (this is an issue if they are pointers to other objects/variables you want copying).
If the copy constructor is marked as deleted, then the object cannot be copied as the compiler doesn't know how its supposed to copy it.
In main function, in line 35th, exception is caught by value, not by reference:
}catch(BadLengthExceptione){
what it means is that in this line, 'e' is a copy of an exception thrown from checkUsername(). It is somehow analogical to passing arguments to functions - you can do it by value, and then copy constructor is called (in other words, a copy of originaly passed variable is created inside of a function), or you can do it by reference, and then original variable is used inside of a function. When you throw an exception you can caught by value - so you're creating a copy of originaly thrown exception, or by reference - and use original exception.
When you call copy ctor of a class, copy ctors of all of its member variables are called as well, so in this example, if a std::stringstream was part of a class, not a local variable of a constructor, a copy ctor of it would have to be called. But because it is marked as deleted, it can't be called, and that is why code can't be compiled.
Inherited Code
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following makes use of sstream. No need to create object on heap:
This makes use of "c_str()" which converts your std::string to const char* (which is what c syntax for representing strings)
That's an error! You returning a pointer to an object (int this case
errorthat is destroyed after function call).That's really dangerous! You need to store the string inside the class so
errorstring must be inside the class.Right, thanks for pointing out
Actually found this out after I posted and the first exception started returning garbage values :/
why did you define stringstream variable inside the constructor? and Why cant I define ss as a class variable, inside the private block ?
Because in here
BadLengthException's copy ctor is being used.
Stringstream's copy ctor is deleted, so if you define it as class variable, then BadLengthException copy ctor is implicitly deleted as well.
So I had this at first (and tried stringstream as a class variable) and couldn't figure out why it wasn't working. It either printed out weird characters or nothing (or spaces?).
Then, I tried testing with cout the num-to-cstring conversion and it prints out the correct value. This actually passed the testcases lol.
This is when I checked the discussion and found elvis_dukaj's solution using stringstream inside the constructor and making the string object a class variable.
So, I'm wondering why the cout works but when using return, it doesn't?
Also, I read Pan_Zloto's explanation but still confused. So I guess I'd like a better explanation. Why can't you use a stringstream class variable but a string class variable works?
because in case of stringsteam on the stack of the function it goes out of scope at the end of a function , so c_str is no longer valid .
Why is there two const?
I didn't really understood this. I don't know much about how the copy constructor works, and when it is deleted. So, looking for some more explanation! Thanks for the help though!
the copy constructor defines how to copy objects of the class "properly". If undefined than it just duplicates the members of the class (this is an issue if they are pointers to other objects/variables you want copying).
If the copy constructor is marked as deleted, then the object cannot be copied as the compiler doesn't know how its supposed to copy it.
Would be great if you could explain more, as per P0kerZ request. :)
In main function, in line 35th, exception is caught by value, not by reference:
what it means is that in this line, 'e' is a copy of an exception thrown from checkUsername(). It is somehow analogical to passing arguments to functions - you can do it by value, and then copy constructor is called (in other words, a copy of originaly passed variable is created inside of a function), or you can do it by reference, and then original variable is used inside of a function. When you throw an exception you can caught by value - so you're creating a copy of originaly thrown exception, or by reference - and use original exception.
When you call copy ctor of a class, copy ctors of all of its member variables are called as well, so in this example, if a std::stringstream was part of a class, not a local variable of a constructor, a copy ctor of it would have to be called. But because it is marked as deleted, it can't be called, and that is why code can't be compiled.
You can read about deleted function here: http://en.cppreference.com/w/cpp/language/function#Deleted_functions
Is it more clear now?
BTW, look at this solution: https://www.hackerrank.com/challenges/inherited-code/forum/comments/399496
Thank you for your explain. I spent very time to understand what is that's problem. the point you said was really perfect and professional.