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Creating memory leak in a C# application. How to do?

Posted on 2011-09-26
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Last Modified: 2012-05-12
Hi there;

I need to create memory leak in a C++ application for test purposes.

How can I achieve that? Moreover, could you provide me a sample code for this?

Kind regards.
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Question by:jazzIIIlove
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by:Kiran Sonawane
Kiran Sonawane earned 400 total points
ID: 36597573
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by:AndyAinscow
ID: 36597594
>>Creating memory leak in a C# application.
>>I need to create memory leak in a C++ application

So which do you want?  
In C# it is possible but not so obvious how.  In C++ it is trivial (assign memory with new but don't delete it afterwards - eg.  char* p = new char;)
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by:oxyoo
ID: 36597596
I am not too experience in this but as far as I know you can't get memory leaks in .Net as in C++ apps, but what you can get in .Net are objects that are not disposed of because they are still being referenced somewhere. So called long lived objects. An (somewhat silly) example of this could be as in the example below where the objects are referenced(leaked) into the list and will not be disposed of.

HTH


public static class FooFactory {
    private static List<Foo> foos = new List<Foo>();

    public static Something CreateSomething() {
        var foo = new Foo();
        foos.Add(foo);
        return foo;
    }
}

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by:oxyoo
ID: 36597600
Oh sorry, read that backwards. Thought you asked for an example in C#, sorry about that.

*runs off and hides*
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by:oxyoo
ID: 36597625
In case it is a C# example you need.. here it is reposted, with some errors removed. Typed too fast.
public static class FooFactory {
    private static List<Foo> foos = new List<Foo>();

    public static Foo CreateMyFoo() {
        var foo = new Foo();
        foos.Add(foo);
        return foo;
    }
}

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by:AndyAinscow
ID: 36597638
@oxyoo
I don't see how that creates a memory leak.  As far as I understand it:- it creates objects that will be later released by the GC mechanism.  No memory leaks anywhere.
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by:oxyoo
ID: 36597652
@AndyAinscow:
Yup, agree with you and that was what I said in the post. It does not create any leaks as such, but it creates long lived objects.

Even though you create a new object using CreateMyFoo, if you only use it for a split second it will not be disposed of since it is still being referenced by the static list.
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by:AndyAinscow
ID: 36597677
That is what I thought.
It depends on the asker of the question - do they really mean a memory leak or do they mean code that just fills available memory up.

And the question of C++ or C# is still open.
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by:jazzIIIlove
ID: 36598374
Ah, sorry, I meant C/C++ but I mistype as I am currently also dealing with another C# application.

But let's go for both then :D

The issue is that I didn't mean to fill up the whole memory but a leak that cause a runtime error which i need.

Regards.
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by:AndyAinscow
AndyAinscow earned 800 total points
ID: 36598408
>>but a leak that cause a runtime error

As far as I know a memory leak will never create a runtime error.

For a leak in C++ you can do the following:
char* p = new char;
//delete p;  /*this will free the assigned memory, comment it out and the memory will leak == never released */
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by:jazzIIIlove
ID: 36598422
Ok, then, how can I crash my program?

I mean does crash mean a runtime error? or Can the outcome of a memory leak be considered as a crash?

Kind regards.
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by:AndyAinscow
AndyAinscow earned 800 total points
ID: 36598764
     int *p = 0;
      (*p) = 42;  //or any other number should do the trick
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by:jazzIIIlove
ID: 36599202
42...
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by:sarabande
sarabande earned 800 total points
ID: 36600062
you could crash your prog by creating more leaks than memory available:

while (true)
{
   p = new unsigned int[1024*1024];
   p[rand()] = rand();
}

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the above code either will throw a memory exception because of too many memory requested (all leaks of 4mb) and crash or will crash because of array access when p finally gets a NULL assigned.

Sara
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by:sarabande
ID: 36600087
of course Andy's code snippet also works. i only wanted to have both the leaks and a crash :)

Sara
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by:jazzIIIlove
ID: 36600570
Thanks. One final question os that is memory leak only way to crash a program? What other ways are there to reproduce a crash for test purpose for C and C# application?

Kind regards.
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Accepted Solution

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sarabande earned 800 total points
ID: 36708927
no, as Andy told memory leaks don't lead to crash. they only reserve free memory where there is no access to from a variabel or pointer. the crash with leaks i produced happens in new operator when no free memory could be found because of too many storage was not freed. some compilers would not crash on new when memory was out but return a NULL pointer. to handle that i added a statement which tries to use a null pointer as array. that would crash in any case. so the crash simulates a situation where a program runs for days or weeks and because of leaks it finally cannot allocate memory.

so crashes can be produced by
- assigning values to a null pointer
- accessing null pointers as arrays
- dividing by zero
- making a memcpy or strcpy where the target pointer is NULL or invalid
- and more ...

higher level functions also may throw exceptions for other reasons. that leads to crash if you don't catch the exception.

Sara

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by:jazzIIIlove
ID: 36708991
Good!
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