Back to General and Gameplay Programming

Dynamic class array: memory leak

General and Gameplay Programming Programming

Started by Xeeynamo February 21, 2012 12:41 AM

10 comments, last by iMalc 12 years, 2 months ago

Xeeynamo

208

Author

February 21, 2012 12:41 AM

Hi!
I'm trying to create an array of classed dynamically, where constructs and destructs are called automatically. This code that I wrote test this thing, but I get memory leaks. How it's possible? I'm deleting every class that I created previously and I delete also the array that holds the classes pointers. In C# it works without problems.
There is the code:



int count;

class Test

{

public:

    int var;

    Test()

    {

	    var = count++;

	    printf("Test() %i\n", var);

    }

    ~Test()

    {

	    printf("~Test() %i\n", var);

    }

};

int main()

{

    count = 0;

    Test *test;

    while(1)

    {

	    test = new Test[10];

	    for(int i=0; i<10; i++)

		    delete &test;

	    delete test;

    }

}

TheUnbeliever

963

February 21, 2012 01:00 AM

You make a single allocation, using new[] (not plain new). You want to make a single use of delete[] - not several of delete.

T* single = new T;

T* array = new T[10];



delete single;

delete[] array;

[TheUnbeliever]

Xeeynamo

208

Author

February 21, 2012 01:17 AM

You make a single allocation, using new[] (not plain new). You want to make a single use of delete[] - not several of delete.

T* single = new T; T* array = new T[10]; delete single; delete[] array;

delete[] ? It was so easy? Now my code works without memory leaks. Thank you so much for your help and sorry for the n00b question.

the_edd

2,109

February 22, 2012 07:54 PM

Someone has to say it: You 'should' be using std::vector<> in C++ for dynamic arrays.

Here's your code converted to do so:



#include <vector>





int count = 0; // initialising absolutely everything is a good habit to get in to, IMO.

class Test

{

public:

    int var;

    Test()

    {

            var = count++;

            printf("Test() %i\n", var);

    }

    ~Test()

    {

            printf("~Test() %i\n", var);

    }

};



int main()

{

    while(1) { std::vector<Test> tests(10); }

}

It should also be noted that the use of 'delete' inside your loop ("delete &test") is very misguided. Make sure you really understand why that's bad.

http://www.mr-edd.co.uk
http://bitbucket.org/edd

Washu

7,836

February 22, 2012 09:02 PM

Someone has to say it: You 'should' be using std::vector<> in C++ for dynamic arrays.

Here's your code converted to do so:

#include <vector> int count = 0; // initialising absolutely everything is a good habit to get in to, IMO. class Test { public: int var; Test() { var = count++; printf("Test() %i\n", var); } ~Test() { printf("~Test() %i\n", var); } }; int main() { while(1) { std::vector<Test> tests(10); } }

It should also be noted that the use of 'delete' inside your loop ("delete &test") is very misguided. Make sure you really understand why that's bad.

*Cough*



int main()

{

    std::vector<Test> tests(10);

}

In time the project grows, the ignorance of its devs it shows, with many a convoluted function, it plunges into deep compunction, the price of failure is high, Washu's mirth is nigh.

the_edd

2,109

February 22, 2012 11:22 PM

*Cough*
int main() { std::vector<Test> tests(10); }

That's not a faithful representation of the O.P's code(?). Though I agree it's far more sensible as a C++-behaviour-discovery mechanism

http://www.mr-edd.co.uk
http://bitbucket.org/edd

slicer4ever

6,773

February 23, 2012 05:23 AM

Someone has to say it: You 'should' be using std::vector<> in C++ for dynamic arrays.

i have to disagree with you in this regard, simply because c++ provides the vector container's for array management, in no way means that you should force yourself to use them.

for what he is demonstrating, understanding the underlying idea's of data management in this regard is much more important, than relying on optional systems to do it for you.

Check out https://www.facebook.com/LiquidGames for some great games made by me on the Playstation Mobile market.

kunos

2,256

February 23, 2012 09:02 AM

simply because c++ provides the vector container's for array management, in no way means that you should force yourself to use them.

Are you suggesting he should rewrite the entire Standard Library? Or that he should use C-like reallocs to do dynamic structures?

The Standard Library IS part of the language, you should come up with a quite big reason not to use it.

As for the OP.. C# != C++ .. it's not the same language with a couple of syntax differences.. it's a different language with different rules. You simply don't "new" things inside a function like that, it's quite slow and messy and, most of the time, useless (ie. there is a better way to do it). And actually, in modern C++ you aren't supposed to use delete at all, ever.

Stefano Casillo
TWITTER: [twitter]KunosStefano[/twitter]
AssettoCorsa - netKar PRO - Kunos Simulazioni

slicer4ever

6,773

February 23, 2012 09:22 AM

[quote name='slicer4ever' timestamp='1329974601' post='4915776']
simply because c++ provides the vector container's for array management, in no way means that you should force yourself to use them.

Are you suggesting he should rewrite the entire Standard Library? Or that he should use C-like reallocs to do dynamic structures?

The Standard Library IS part of the language, you should come up with a quite big reason not to use it.
[/quote]

Not at all, i never made this claim. All I'm saying is that the standard library isn't required for every situation. and particularly for this situation, it appeared that he was simply trying to learn basic constructor/destructor workings, and basic memory management. telling him instead to use standard library methods to do all his memory management is just creating a programmer whom doesn't understand the basics in terms of memory management.

in modern C++ you aren't supposed to use delete at all, ever.

I have never heard this before.

Check out https://www.facebook.com/LiquidGames for some great games made by me on the Playstation Mobile market.

kauna

2,925

February 23, 2012 11:42 AM

Nobody wrote this down so just to clear up things:

you should use delete with new and delete[] with new[], otherwise you'll end up in some undefined behaviour zone.

Otherwise std::vector and other standard library templates will make your life easier in many cases.

Cheers!

Dynamic class array: memory leak

This topic is closed to new replies.

Popular Topics

Recommended Tutorials

Dynamic class array: memory leak

This topic is closed to new replies.

Popular Topics

Recommended Tutorials

Reticulating splines