Using C implement class with dynamic memory allocation using constructor,destructor and copy constructor.Algorithm. Mohanraj No comments. Implement class with dynamic memory allocation. To implement class with dynamic memory allocation using constructor,destructor and copy constructor.Algorithm. May 08, 2018 I attached bellow the code for Matrix Multiplication for any proper order with dynamic memory allocation. For completeness I used 3 different methods for matrix multiplication: one function double. multMatrixpf (see equivalent function Fortran/Pascal) and two subroutine/procedure(Fortran/Pascal like), where by first void multMatrixp you need to.
noob here. I'm doing an exercise from a book and the compiler reports no errors, but the program crashes when I try to run it.
I'm trying to run a little program exercising the different methods of the Cow class. It explicitly has: a constructor, a default constructor, a copy constructor, a destructor, an overloaded assignment operator, and a method to show its contents.
I'll put the whole project:
Class specification:
Methods implementation:
Client:
I was hiding some parts of the code to locate the possible problem and it seems the progam doesn't like this two lines:
And in particular, in the overloaded assignment operator and the copy constructor, if I hide the
delete[] temp
line, the program doesn't crash.I'm total noob and probably is something stupid but I can't see what I'm doing wrong in these definitions.
Any help?
Kurospidey
KurospideyKurospidey
2 Answers
It's the copy c-tor. There is no previously allocated members.
this->hobby
points to random garbage. So when you delete[] temp
(i.e. this->hobby
before the new assignment), you get UB.![Cell Cell](/uploads/1/2/4/7/124715051/922141311.jpg)
hobby = name
is incorrect, as it causes a memory leak + destructor will try to delete an object that was not allocated with operator new[]
.ForEveRForEveR
@ForEveR Already noted that your copy constructor is deleting memory that was never allocated.
But I'm going to argue that the entire exercise is flawed and is teaching C with classes, NOT C++. If you used string all your problems would go away because you wouldn't have to manage resources directly. This eliminates the need for you to write a destructor or copy assignment/constructor entirely. For example:
Mark BMark B
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I have written a code to find sum of two matrices using dynamic allocation and operator overloading.
When I execute, I get stuck at
matrix operator+(matrix &m4,matrix &m5)
.I searched on internet but I'm unable to find my error.So, what's wrong with my code? It works fine in Code::Blocks but not in Xcode.
SkrewEverythingSkrewEverything
2 Answers
Problems I see in your code:
- You have code to allocate memory in constructor and deallocate memory in the destructor. However, you have not implemented a copy constructor or a copy assignment operator. This leads to lots of problems. See The Rule of Three.
- The second argument to
operator>>
needs to be a reference. Otherwise, you'll end up reading data into a local variable. There won't be any change to the object that you used to call it.Another unwanted side effect of not having implemented the copy constructor is that you end up using dangling pointers when this function returns, which is cause for undefined behavior. - The second argument to
operator<<
should be aconst&
. Otherwise, you'll needlessly make a copy of the object and delete it.This function will also result in dangling pointers due to the missing copy constructor.
The copy constructor can be implemented as:
I'll leave you to implement the copy assignment operator.
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R SahuR Sahu
The problem stems from pass by value in place of pass by reference, but this exposed a complete lack of Rule of Three compliance.
R Sahu has demonstrated the copy constructor to resolve the Rule of Three problem.
I'm going to take a different route: Die Array, DIE!
Unlike a standard stupid array, std::vector is Rule of Three Compliant. Using it for 2 Dimensions is pretty painless:
Vector makes this program rule of 3/5 compliant, which means you can copy and move Matrix objects with dramatically reduced debugging adventures. You gain nothing from using an array instead of a vector unless the array is of a fixed size, so think carefully before using one.
Note the change in name.
matrix
is already used by the class, so a bit of fuddle takes care of naming confusion. I do a bit more renaming for similar reasons:![Use Constructor Dynamic Memory Allocation For Matrix In C Use Constructor Dynamic Memory Allocation For Matrix In C](/uploads/1/2/4/7/124715051/192913324.png)
The constructor now looks like this:
The friend functions get a slight make-over to get better naming and to use references where they are needed:
And the rest can go pretty much unchanged.
But there is an even better way to do this:
This layout is much faster because of spatial locality assisting in caching data as you're working. The 2 D array approach has number of rows +1 different array that may be in very different places in RAM, leading to an increase in cache misses and time lost to reading data that could have already been read if all the data was in one place.
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